CUNY Kingsborough Community College Organic Chemistry Labs Questions

For Expt#1 use the following table for data (cross out the column for Thiel’s Tube in the labmanual table)
Group
Mol% of cinnamic acid and urea
1
2
3
Pure cinnamic acid
Pure urea
80 mol% cinnamic acid and 20 mol%
urea
60 mol% cinnamic acid and 40 mol%
urea
40 mol% cinnamic acid and 60 mol%
urea
20 mol% cinnamic acid and 80 mol%
urea
4
5
6
Melting Point
Electronic Device 0C
134, 132
132, 130
128, 126
Class average 0C
120, 122
121
116, 114
115
122, 124
123
133
131
127
1) Draw the Lewis structure, condensed structures and line angle formula for the
following two compounds (6 points)
a) C5H10O
b) C4H7N
2) Draw the resonance structures for the following compounds? (4 points)
a)
b)
c)
d)
3) Arrange the following compounds in the order of increasing acidity (use pKa
Values). (2 points)
Butane, 1-Butanol, water, 1-Butyne, 2-butene
4) Identify a nucleophile (base) and an electrophile(acid) between the following two
reactants: reactant A is CH3ONa and reactant B is CH3CH2Br. Indicate which
atom in a nucleophile donates a pair of electrons to what atom
in electrophile THAT gains electron in forming a bond. Finally write CHEMICAL
EQUATION for the above reaction. (reactants and products). (4 points)
5) Make up a chemical equation similar to the question above. (2 points)
1. Arrange the following compounds in the order of increasing boiling points (3 points)
a) Hexane
b) 2,2-dimethylpropane
c)1-pentanol
d) 2,3-dimethylbutane
e) 2-methyl-2-butanol
2. Indicate the hybridization for the following compounds ( 2 points)
a) Propane
b) 2-Butene
c) 1-pentyne
3. Arrange the following intermolecular forces in order of increasing strength (least to
highest). Explain these each intermolecular force in 2 sentences. (6 points)
Hydrogen bonding, London dispersion forces, dipole-dipole forces.
4. Circle and identify each functional group in chemical structure of anticancer drug Taxol
as shown below (4 points)
EXPERIMENT 1
Melting Point Determination
Objective
The purpose of this experiment is to determine the melting point, experience the use of
the melting point apparatus, and learn the use of melting points to identify unknown
compounds.
Introduction
Students will be synthesizing different solid compounds in two semesters of organic
chemistry lab. By determining the melting point, students will come to know whether or
not the right compound has been synthesized and the purity of the compound. Students
will determine melting points before submitting certain products that they will synthesize
in future labs. Therefore, learning the method of how to determine the melting point will
be useful in the future lab experiments.
The melting point can be defined as the temperature at which a transition from solid to
liquid occurs. Melting points serves two important purposes: First, an unknown pure
solid can be identified by determining its melting point because it is highly unlikely that
two compounds would have the exact same melting point. Second, to determine if a given
substance is pure or impure. If the compound melts at narrow melting point range (1-2
°C) then the compound is pure. While if the compound melts at lower and wider melting
point range then the compound is impure.
To establish the identity of a sample, the mixed melting points or the melting points
of the mixtures are frequently performed. To identify the unknown solid a mixed
melting point method is used. If the mixture consists of both an unknown and a known
substance that gives a sharp melting point range, then the unknown (mixed with the
known) is identical to the known. However, if the mixture consists of both an unknown
and a known substance that gives a lower and wider melting point range, then an impurity
(known) is introduced into the unknown. Salt placed on icy roadways is an example of a
mixed melting point. Ice is assumed to be pure and melts at 0 °C and salt is an impurity.
The ice-salt mixture melts at a lower temperature.
Calibration of a Thermometer
One should calibrate the thermometer before taking the melting point of any
compound. The normal freezing point (0 °C) and boiling point (100 °C) of water are
calibration points for a thermometer. We obtain actual value on a given thermometer for
ice-water slush and for boiling water.
Experimental Procedure
Part I You do not have to do Part I but have to make sure that the mercury thread in
the thermometer is not broken.
1. Place the thermometer in an ice-water mixture and allow it to obtain the
temperature for the melting point of ice (freezing point of water).
2. Set up apparatus as shown in Figure 1.1, add a small magnetic stir bar, and bring
water to boil, using a hot plate. After the temperature of the thermometer reaches
a stationary reading, record the value for the boiling point of water.
Figure 1.1 Calibration of 100°C point on thermometer
Calibration curve: Plot the actual temperature reading obtained for the melting point
of ice and the actual temperature reading for the boiling point of water versus the true
freezing point 0 °C and the true boiling point of water 100 °C, corrected for difference
in pressure compared to 760 Torr (Table 1) and Figure 1.2. You can find a table of
the boiling point of water corrected for pressure in a chemical handbook. To obtain
the actual temperature reading, draw a vertical line (AB) from the thermometer
reading scale to intersect the sloped line at point B. Then draw a horizontal line (BC)
to the true temperature value scale. Point C is the true temperature. In practice, these
variations are so slight that they are often ignored. They are frequently so small that
they cannot be read on a graph.
Calculation of Correct Temperature
You can calculate the true temperature by the following formula
T = (t-Tmp) 100 °C /tbp-t mp
Where
T= true temperature
t=Celsius temperature reading
Tmp =
p = water melting point reading on Celsius thermometer
T bp = water boiling point reading on Celsius thermometer
Table 1.1 Boiling point of Water versus Atmospheric Pressure (Degree fractions)
Temperature,
°C 0.0
0.2
0.4
0.6
0.8
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
433.6
450.9
468.7
487.1
506.1
525.76
546.05
566.99
588.60
610.90
633.90
657.62
682.07
707.27
733.24
760.00
787.57
437.0
454.4
472.4
491.0
510.0
529.77
550.18
571.26
593.00
615.44
638.59
662.45
687.04
712.40
738.53
765.45
798.82
440.4
458.0
476.0
494.7
513.9
533.80
554.35
575.55
597.43
620.01
643.30
667.31
692.05
717.56
743.85
770.93
798.82
440.4
461.6
479.8
498.5
517.8
537.86
558.53
579.87
601.89
624.61
648.05
672.20
697.10
722.75
749.20
776.44
804.50
447.5
465.2
483.4
502.2
521.8
541.95
562.75
584.22
606.38
629.24
652.82
677.12
702.17
727.98
754.58
782.00
810.21
260 –
200
–
100
0
1
0
1
260
100
200
Figure 1.2 Calibration curve of a thermometer with inaccurate readings: freezing
point = 1 °C and boiling point = 102°C at 760 mm Hg or 760 Torr
Part II
Procedure to determine a melting point
1. Place a small amount of powdered sample on a watch glass. Obtain a capillary
tube (capillary tube is closed at one end and open at another end). Hold the
capillary tube at the middle and make contact with the sample with the open-end.
Use little force to collect sample into the capillary tube. Hold the capillary tube
with two fingers vertically with the open-end top and the closed end at the
bottom. Gently tap the capillary tube on the bench top or vibrate the tube with a
file allowing the sample to travel to the closed end of the tube. Alternatively, to
move the solid to the closed end of the capillary tube: Take a piece of 6-8 mm
diameter plastic tube (open both ends) about 0.5 meter long, and place it vertically
on a hard surface (bench top), drop the capillary tube with closed end bottom
through the large tube several times with its sealed end down. There should be
approximately 2 mm of sample in the tube, just enough to see it clearly.
2. Melting Point apparatus: A simple type of melting point apparatus is the Thiele
tube, shown in Figure 1.3. This tube was shaped meticulously so that the heat
applied to the side arm by a micro-burner is distributed evenly to all parts of the
vessel by convection current, and therefore stirring is not required. Proper use of
the Thiele tube is required to obtain reliable melting points. Secure the capillary
tube to the thermometer at the position indicated in the Figure 1.3(b), using either
a rubber band or a small segment of rubber tubing. Be sure that the band holding
the capillary tube on the thermometer is as close to the top of the tube as possible.
Support thermometer and the attached capillary containing the sample in the
apparatus either with a cork as shown in Figure 1.3(a), or by carefully clamping
the thermometer so that it is immersed in oil. The thermometer and the capillary
tube must not contact the glass of the Thiele tube. Since the oil will expand upon
heating, make sure that the height of the heating fluid is approximately at the level
indicated in Figure 1.3(a), and that the rubber band is in the position indicated.
Otherwise, the hot oil will come in contact with the rubber, causing the band to
expand and loosen: The sample tube may then fall into the oil. Heat the Thiel tube
at the rate of 2-3 °C per minute. The Thiele tube has been replaced in many
laboratories by various electric melting point devices. You will be using electric
melting point device to determine melting points in future labs.
Thermometer
Thermometer
Capillary tube
Slice of rubber tubing
Capillary tube
Slice of Rubber
tubing
Thiele tube
Sample
Microburner
b)
Figure 1.3 (a) Thiele melting point apparatus (b) Arrangement of sample and thermometer.
In order to gain some practice, determine the melting point of pure urea and cinnamic
acid and each of the mixtures supplied by the instructor. Make a plot of melting point
versus percentage composition of the mixture as shown Figure 1.4.
H
H
0
H2N NH2
COOH
Cis-cinnamic acid
Urea
EXPERIMENT 1
Melting Point Determination
Objective
The purpose of this experiment is to determine the melting point, experience the use of
the melting point apparatus, and learn the use of melting points to identify unknown
compounds.
Introduction
Students will be synthesizing different solid compounds in two semesters of organic
chemistry lab. By determining the melting point, students will come to know whether or
not the right compound has been synthesized and the purity of the compound. Students
will determine melting points before submitting certain products that they will synthesize
in future labs. Therefore, learning the method of how to determine the melting point will
be useful in the future lab experiments.
The melting point can be defined as the temperature at which a transition from solid to
liquid occurs. Melting points serves two important purposes: First, an unknown pure
solid can be identified by determining its melting point because it is highly unlikely that
two compounds would have the exact same melting point. Second, to determine if a given
substance is pure or impure. If the compound melts at narrow melting point range (1-2
°C) then the compound is pure. While if the compound melts at lower and wider melting
point range then the compound is impure.
To establish the identity of a sample, the mixed melting points or the melting points
of the mixtures are frequently performed. To identify the unknown solid a mixed
melting point method is used. If the mixture consists of both an unknown and a known
substance that gives a sharp melting point range, then the unknown (mixed with the
known) is identical to the known. However, if the mixture consists of both an unknown
and a known substance that gives a lower and wider melting point range, then an impurity
(known) is introduced into the unknown. Salt placed on icy roadways is an example of a
mixed melting point. Ice is assumed to be pure and melts at 0 °C and salt is an impurity.
The ice-salt mixture melts at a lower temperature.
Calibration of a Thermometer
One should calibrate the thermometer before taking the melting point of any
compound. The normal freezing point (0 °C) and boiling point (100 °C) of water are
calibration points for a thermometer. We obtain actual value on a given thermometer for
ice-water slush and for boiling water.
Experimental Procedure
Part I You do not have to do Part I but have to make sure that the mercury thread in
the thermometer is not broken.
1. Place the thermometer in an ice-water mixture and allow it to obtain the
temperature for the melting point of ice (freezing point of water).
2. Set up apparatus as shown in Figure 1.1, add a small magnetic stir bar, and bring
water to boil, using a hot plate. After the temperature of the thermometer reaches
a stationary reading, record the value for the boiling point of water.
Figure 1.1 Calibration of 100°C point on thermometer
Calibration curve: Plot the actual temperature reading obtained for the melting point
of ice and the actual temperature reading for the boiling point of water versus the true
freezing point 0 °C and the true boiling point of water 100 °C, corrected for difference
in pressure compared to 760 Torr (Table 1) and Figure 1.2. You can find a table of
the boiling point of water corrected for pressure in a chemical handbook. To obtain
the actual temperature reading, draw a vertical line (AB) from the thermometer
reading scale to intersect the sloped line at point B. Then draw a horizontal line (BC)
to the true temperature value scale. Point C is the true temperature. In practice, these
variations are so slight that they are often ignored. They are frequently so small that
they cannot be read on a graph.
Calculation of Correct Temperature
You can calculate the true temperature by the following formula
T = (t-Tmp) 100 °C /tbp-t mp
Where
T= true temperature
t=Celsius temperature reading
Tmp =
p = water melting point reading on Celsius thermometer
T bp = water boiling point reading on Celsius thermometer
Table 1.1 Boiling point of Water versus Atmospheric Pressure (Degree fractions)
Temperature,
°C 0.0
0.2
0.4
0.6
0.8
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
433.6
450.9
468.7
487.1
506.1
525.76
546.05
566.99
588.60
610.90
633.90
657.62
682.07
707.27
733.24
760.00
787.57
437.0
454.4
472.4
491.0
510.0
529.77
550.18
571.26
593.00
615.44
638.59
662.45
687.04
712.40
738.53
765.45
798.82
440.4
458.0
476.0
494.7
513.9
533.80
554.35
575.55
597.43
620.01
643.30
667.31
692.05
717.56
743.85
770.93
798.82
440.4
461.6
479.8
498.5
517.8
537.86
558.53
579.87
601.89
624.61
648.05
672.20
697.10
722.75
749.20
776.44
804.50
447.5
465.2
483.4
502.2
521.8
541.95
562.75
584.22
606.38
629.24
652.82
677.12
702.17
727.98
754.58
782.00
810.21
260 –
200
–
100
0
1
0
1
260
100
200
Figure 1.2 Calibration curve of a thermometer with inaccurate readings: freezing
point = 1 °C and boiling point = 102°C at 760 mm Hg or 760 Torr
Part II
Procedure to determine a melting point
1. Place a small amount of powdered sample on a watch glass. Obtain a capillary
tube (capillary tube is closed at one end and open at another end). Hold the
capillary tube at the middle and make contact with the sample with the open-end.
Use little force to collect sample into the capillary tube. Hold the capillary tube
with two fingers vertically with the open-end top and the closed end at the
bottom. Gently tap the capillary tube on the bench top or vibrate the tube with a
file allowing the sample to travel to the closed end of the tube. Alternatively, to
move the solid to the closed end of the capillary tube: Take a piece of 6-8 mm
diameter plastic tube (open both ends) about 0.5 meter long, and place it vertically
on a hard surface (bench top), drop the capillary tube with closed end bottom
through the large tube several times with its sealed end down. There should be
approximately 2 mm of sample in the tube, just enough to see it clearly.
2. Melting Point apparatus: A simple type of melting point apparatus is the Thiele
tube, shown in Figure 1.3. This tube was shaped meticulously so that the heat
applied to the side arm by a micro-burner is distributed evenly to all parts of the
vessel by convection current, and therefore stirring is not required. Proper use of
the Thiele tube is required to obtain reliable melting points. Secure the capillary
tube to the thermometer at the position indicated in the Figure 1.3(b), using either
a rubber band or a small segment of rubber tubing. Be sure that the band holding
the capillary tube on the thermometer is as close to the top of the tube as possible.
Support thermometer and the attached capillary containing the sample in the
apparatus either with a cork as shown in Figure 1.3(a), or by carefully clamping
the thermometer so that it is immersed in oil. The thermometer and the capillary
tube must not contact the glass of the Thiele tube. Since the oil will expand upon
heating, make sure that the height of the heating fluid is approximately at the level
indicated in Figure 1.3(a), and that the rubber band is in the position indicated.
Otherwise, the hot oil will come in contact with the rubber, causing the band to
expand and loosen: The sample tube may then fall into the oil. Heat the Thiel tube
at the rate of 2-3 °C per minute. The Thiele tube has been replaced in many
laboratories by various electric melting point devices. You will be using electric
melting point device to determine melting points in future labs.
Thermometer
Thermometer
Capillary tube
Slice of rubber tubing
Capillary tube
Slice of Rubber
tubing
Thiele tube
Sample
Microburner
b)
Figure 1.3 (a) Thiele melting point apparatus (b) Arrangement of sample and thermometer.
In order to gain some practice, determine the melting point of pure urea and cinnamic
acid and each of the mixtures supplied by the instructor. Make a plot of melting point
versus percentage composition of the mixture as shown Figure 1.4.
H
H
0
H2N NH2
COOH
Cis-cinnamic acid
Urea
Liquid solution of X+Y
Temperature in °C
Liquid
Solid XI
Liquid +
Solid Y
100
80
60
40
20
0
(Cinnamic acid) mol%X
(Urea mol% Y
0
20
40
60
80
100
Composition
Figure 1.4 Melting point composition diagram for two hypothetical solids, X and Y
Each student will determine the melting point of either pure cinnamic acid or pure urea
using the Thiele’s tube, and another mixture using the electric melting point device. The
melting point data for the whole class will be recorded in Table1.1.
Calculation of 80 mol% cinnamic acid + 20 mol% urea is shown below.
Calculation
To determine melting point you require small amounts of samples. Therefore, milligrams
of samples are good enough.
80 mol% cinnamic acid =
80 mol cinnamic acid
100
80 mmol% cinnamic acid =
80 mmol cinnamic acid
100
mg. of cinnamic acid =
80 mmol cinnamic acid
100
x 148 mg of cinnamic acid
1 mmol cinnamic acid
= 118.4 mg. of cinnamic acid
20 mol% urea
20 mol urea
100
20 mmol% urea
20 mmol urea
100
mg. of urea
20 mmol urea
100
x 60.06 mg of urea
1 mmol urea
12.0 mg. of urea
Place 118.4 mg of cinnamic acid, and 12.0 mg of urea on a watch glass, mix the mixture
using a spatula, and determine the melting point as per the procedure.
Similarly, the students should calculate the mol percentages of 60 mol% cinnamic acid +
40 mol% urea, 40 mol% cinnamic acid + 60 mol% urea, 20 mol% cinnamic acid + 80
mol% urea, 60 mol% cinnamic acid + 40 mol% urea. Mix thoroughly each one of the
mixtures and then determine the melting point.
Melting Point ( °C)
Class Average (°C)
Thiele’s Tube
Electric Device
Table 1.1 Melting point data
Group
Mol % of
cinnamic acid
and urea
Pure cinnamic
1. acid
2. Pure Urea
3.
4.
80 mol%
cinnamic acid +
20 mol% urea
60 mol%
cinnamic acid +
40 mol% urea
40 mol%
cinnamic acid +
60 mol% urea
20 mol%
cinnamic acid +
80 mol% urea
5.
6.
Record all your results in the lab notebook.
Lab Report: Lab report includes a cover sheet, objective, Table 1.1, diagram similar
to Figure 1.4 on a graph paper, and conclusions.
EXPERIMENT 1
Lab Report
Title of experiment
Objective
Results
Melting Point (°C)
Class Average (°C)
Thiele’s Tube
Electric Device
Table 1-1 Melting point data
Group Mol % of
cinnamic acid
and urea
Pure cinnamic
1.
acid
2. Pure Urea
3.
4.
80 mol%
cinnamic acid +
20 mol% urea
60 mol%
cinnamic acid +
40 mol% urea
40 mol%
cinnamic acid +
60 mol% urea
20 mol%
cinnamic acid +
80 mol% urea
5.
6.
Conclusions (One or two sentences only)
Post-Laboratory Questions.
1. What procedure do you use to determine the identity of cinnamic acid and urea given
that they have the same melting point?
2. What do you conclude regarding purity of the following samples given the following
melting points?
a) 133-134 °C
b) 70-96 °C
3. Indicate whether the following statements are True or False.
a) An impurity always increases the melting point of an organic compound.
b) A pure organic compound always melts at sharp melting point.
4. Comment on the green chemistry of this experiment. That is, the nature and amount of
solvent (for example water, etc.), and atom economy (number of atoms in the reactants
versus products) in this experiment.
A good lab notebook should consist of the following:
Experimental Write-up
Title: Experiment title and date.
Reference: This is where you found the experiment. The source can be a lab manual.
Purpose of the experiment: A brief, one sentence description of the experiment.
Investigative experiments: These experiments include recrystallization, distillation, and
qualitative organic analysis. You must interpret the data or
observations. These observations include color changes,
melting points, and boiling points.
Preparation experiments:
Table of Physical Constants. Fill out the table in these experiments before you start. For
each material, you must record the following: grams, molecular weight, number of moles,
density, melting point, and boiling point.
Complete equation and mechanism.
Precautions.
Diagram- Diagram of the experimental write-up.
Procedure- It is important to write concise, step-by-step procedures to be followed in the
laboratory.
Experimental Observations- Faithfully record all data and observations in the lab
notebook.
Yield Data- Calculate the percent yield from genuine yield and theoretical yield.
Lab Report: Simply transfer the data directly from the completed lab notebook to a lab
report.
A good lab notebook should consist of the following:
Experimental Write-up
Title: Experiment title and date.
Reference: This is where you found the experiment. The source can be a lab manual.
Purpose of the experiment: A brief, one sentence description of the experiment.
Investigative experiments: These experiments include recrystallization, distillation, and
qualitative organic analysis. You must interpret the data or
observations. These observations include color changes,
melting points, and boiling points.
Preparation experiments:
Table of Physical Constants. Fill out the table in these experiments before you start. For
each material, you must record the following: grams, molecular weight, number of moles,
density, melting point, and boiling point.
Complete equation and mechanism.
Precautions.
Diagram- Diagram of the experimental write-up.
Procedure- It is important to write concise, step-by-step procedures to be followed in the
laboratory.
Experimental Observations- Faithfully record all data and observations in the lab
notebook.
Yield Data- Calculate the percent yield from genuine yield and theoretical yield.
Lab Report: Simply transfer the data directly from the completed lab notebook to a lab
report.
EXPERIMENT 2
Recrystallization of Crude Acetanilide or Benzoic Acid
Objective
The goal of this experiment is to purify the solid compounds by recrystallization, and
characterize them by melting point, and learn the technique of recrystallization.
Introduction
Organic Chemists devote considerable effort to the isolation of pure compounds from
Natural Products (e.g. Eugenol from Cloves, Expt. # 7), and syntheses of many useful
compounds in the laboratory. The solid compounds that are isolated or synthesized are
purified by recrystallization. Recrystallization is one of the methods most often used
for purification of solids. Sublimation, extraction, and chromatography are the other
methods used to purify the solids. However, to achieve the highest purity, solids purified
from one of the above alternative methods may still be recrystallized.
Generally all solids are more soluble in a hot solvent than in cold. The solid
compound that is to be purified is dissolved in an appropriate solvent at elevated
temperature. Any impurities present in the solid will remain undissolved in the solution.
The hot solution will be filtered to remove impurities. The filtrate thus obta
ined cooled to room temperature or below 0 °C to form pure crystals. Furthermore, the
pure solid crystals will be obtained by second filtration. If the impurities present in the
original solid mixture have dissolved and remain dissolved after the solution is cooled,
filtration of the crystals that have formed should ideally provide a pure compound. The
common solvents used in recrystallizaion are listed in Table 2.1.
Flammable
Table 2.1 Common solvents used in recrystallization.
Solvent
Boiling Point “C Water
(1 atm.) soluble
Methanol
65
Yes
Ethanol (95%)
78
Yes
Diethyl Ether (Ether)
35 Slightly
Methylene chloride
41
No
Acetone
56
Yes
Ethyl acetate
77
Yes
Tetrahydrofuran
65
Yes
Cyclohexane
81
No
Toluene
111
No
Water
100
Yes
Dielectric
Constant (6)
32.5
24.4
4.4
9.0
20.5
6.1
7.4
1.8
2.5
78.4
Yes
Yes
Yes
No
Yes
Yes
Yes
Yes
Yes
No
Chemical structures of common solvents used for recrystallization are shown below.
CH3CH2OH
CH3OH
Methanol
CH3CH OCH2CH3
Ethyl ether(ether)
Ethanol
CH2Cl2
CH3CCH3
CH3COCH2CH3
Methylene chloride
Acetone
Ethyl acetate
CH3
Tetrahydrofuran
Cyclohexane
Toluene
Students will synthesize many solid compounds in the future experiments, and
therefore should write down the following details about the selection of a solvent, and a
detailed experimental procedure in their lab notebooks to refer back when necessary.
Selecting A Solvent
To obtain a compound of high purity and good recovery or yield, perhaps the choice
of selecting a solvent is very important. The recrystallization solvent should satisfy the
following criteria. (1) The solid compound being recrystallized should be reasonably
soluble in the hot solvent (about 1g/20 mL), and insoluble in the cold solvent. (2) The
impurities should be insoluble in the solvent at all temperatures; otherwise, both would
crystallize from solution simultaneously. (3) The solvent should have low boiling point in
order to remove it readily from the crystals. (4) Generally, the boiling point of the solvent
should be lower than the melting point of the solid to be recrystallized. (5) Chemically
the solvent should not react with the solid compound being purified.
Polar compounds are soluble in polar solvents, and nonpolar compounds are soluble in
nonpolar solvents. Simply this generalization is stated as, “like dissolves like”. The
series of solvents in Table 2.1 demonstrate that these solvents range widely in polarity
measured by the dielectric constant (€). The solvents with dielectric constants between 2-
3 are non polar, above 10 are polar, and between 3-10 are of intermediate polarity. A
mixture of solvents (mixed solvents) is sometimes required for recrystallization. The
mixed solvent is usually composed of usually two solvents; sometimes three solvents
may be used. In two solvent systems, one of these solvents dissolves the compound to be
purified even in cold and the other one does not.
Note: Before doing the experiment, record the solubility of acetanilide and benzoic acid
from the Lange’s Hand Book of Chemistry.
Solubility of Acetanilide at 25°C:
in 100 parts of water
Solubility of Benzoic acid at 17.5°C:
in 100 parts of water
Solubility of Benzoic acid at 750 c:
in 100 parts of water
All the data should be entered in Table 2.2.
Experimental Procedure
1. Weigh 2.0 g of solid (acetanilide or benzoic acid) to be purified and place in a
250-ml beaker along with a magnetic stir bar. Add few milliliters (-60 mL) of
solvent (water) to the beaker, and the mixture is then heated to boiling (b.p. of
water is 100° C) on a hot plate as shown in Figure 2.1.
Figure 2.1 Crude solid on a hot plate for recrystallization
2. More water is added to the hot mixture in small portions (- 1 mL) using a Pasteur
pipet or a medicinal dropper or small (10-mL) graduated cylinder until the solid
completely dissolves. It is important to let boiling resume after each addition so
that the minimum amount of solvent is used to effect dissolution. Using excessive
amount of solvent decreases the recovery of the solid compound. (You may need
a total 100 mL of water or more to dissolve the solid).
3. Make a fluted filter paper from a flat piece of round filter paper. Fold the filter
paper in half and then into quarters. Place the fluted filter paper in the stem-less
funnel and add ~ 1 mL of hot water into the filter paper so that it snuggly fits in.
Filter the hot solution through the fluted filter paper using a hot hand as shown in
Figure 2.2. Filtering through the fluted filter paper increases the rate and ease of
filtration because fluting increases the surface area the paper contacted by the
liquid being filtered. Retrieve the magnetic stir bar from the fluted filter paper and
return it to the front desk.
15
Ring support
0
0
Figure 2.2 Filtering a hot solution
4. The filtrate thus obtained should be allowed to cool to room temperature or
slightly above and then placed in ice-water slush as shown in Figure 2.3. After 15
minutes or so the crystals of the compound should be formed.
Ice-water
Figure 2.3 Cooling a filtered solution
5. Filtration: To a stand, clamp a Filter flask fitted with a Buchner funnel for
vacuum filtration as shown in Figure 2.4. Place a suitable filter paper that covers
all the holes in the Buchner funnel and pour 1 mL of cold water. Apply vacuum
very slightly so that filter paper snuggly fits in and covers all the holes in the
Buchner funnel. Pour the crystals from the beaker into the Buchner funnel while
vacuum is on. The wet crystals contain traces of water in it and therefore the
crystals must be dried before determining melting point.
Buchner funnel
Filter paper
Black rubber ring
Vacuum
Mb
W
00
Filter flask
Figure 2.4 Apparatus for vacuum filtration using Filter flask and Buchner funnel
6. Carefully remove the crystals and the filter paper from the Buchner funnel using a
spatula. Keep it on a watch glass and leave it open to air-dry and lock the draw.
Table 2.2 Recrystallization of benzoic acid or acetanilide
Name of the Name of the Grams of Grams of m.p of the Recovery /
crude solvent used for crude recovered crystallized percentage
compound recrystallization compound /crystallized compound yield
compound
Grams of recrystallized or pure compound
Recovery/percentage yield =
X 100%
Grams of crude compound
The first thing to do in the next lab period is to determine the melting point using the
electric melting point device. Record the melting point of the compound in your lab
notebook along with all other results.
Lab report: Submit the lab report the next lab. The lab report must include a cover sheet,
objective, Table 2.2, percentage yield, and conclusions.
EXPERIMENT 2
Lab Report
Title of experiment
Objective
Results
Table 2.2 Recrystallization of benzoic acid or acetanilide
Name of the Name of the Grams of Grams of M.p of the Recovery /
crude solvent used for crude recovered crystallized percentage
compound recrystallization compound crystallized compound yield
compound
Grams of recrystallized or pure compound
Recovery/percentage yield
X 100%
Grams of crude compound
Conclusions (one or two sentences only)
Post-Laboratory Questions.
1. How do you know that the given solid is pure or impure? Explain.
2. What are the criteria for selection of a recrystallizing solvent?
3. What is the purpose of filtering hot solution?
4. Comment on the green chemistry of this experiment. That is, the nature and amount of
solvent (for example water, etc.), and atom economy (number of atoms in the reactants
versus products) in this experiment.
Week 2
Chapter 2
Read: Chapter 2. Structure and Properties of Organic
Molecules
Learning Activity: Molecular orbitals. Hybridization and
molecular shapes. Drawing three-dimensional molecules.
Rotation of single bonds, rigidity of double bonds, isomerism.
Predict the molecular geometry of an organic compound using
hybridization theory. Polarity of bonds and molecules.
Distinguish between covalent and non-covalent bonding in
organic molecules. Intermolecular forces. Predict physical
properties that result from weak intermolecular interactions.
Brief description of various types of hydrocarbons, oxygen
and nitrogen containing organic molecules (functional
EXPERIMENT 3
Molecular Models
Objective
In this lab you will get a hands on experience with molecular models. You will build
different organic molecules and draw them in three-dimensional shapes.
Introduction
Isomerism. Isomerism has been defined as the phenomenon where two or more different
compounds are represented by identical molecular formulas. Isomers are compounds that
have identical molecular formulas but different molecular structures. In other words,
isomers are compounds that have the same numbers and same kinds of atoms, but differ
in the way the atoms are connected or bonded.
The following flow chart shows different types of isomers.
isomers
stereoisomers
constitutional isomers
(structural isomers)
diastereomers
enantiomers
skeletal
isomers
positional
isomers
functional
isomers
other diastereomers
cis-trans isomers
geometrical isomers
Constitutional isomers are isomers in that their atoms are connected differently.
Constitutional isomers are subdivided into three isomers: skeletal isomers, positional
isomers, and functional isomers.
Skeletal isomers. These isomers have same molecular formula but differ in carbon
skeleton. For example, there are 2 different structures for butane, C4H10. The following
two structures differ in the carbon skeleton; that is, the structure for n-butane is a
continuous chain of carbon skeleton, where as in isobutene, the structure is branched
chain of carbon skeleton. These two compounds are very different and they have different
physical and chemical properties.
H
H
H
H
3
H
H
H
3
H
H
2
H
2
H
H н
H
H
H н
H
H
H н
2
H
Н.
IUPAC: n-butane
IUPAC: 2-Methylpropane
Common Name: Isobutane
Positional isomers. The carbon skeleton of the positional isomers is the same, but they
differ in the position of other atoms such as halogens. For example, n-propyl bromide and
isopropyl bromide have the molecular formulas CzH;Br but differ in the position of the
bromine atom in the three-carbon chain.
H
Н.
H
H
3
Н.
H
H
I
2
Br
H
I
H
IN
H н
H
H н
Br
IUPAC: 1-Bromopropane
Common Name: Propyl bromide
IUPAC: 2-Bromopropane
Common Name: Isopropyl bromide
Functional isomers. Compounds have same molecular formula but they differ in the
position of atoms other than carbon (oxygen etc.). Molecules have same molecular
formula but different functional groups. For example, a compound with the formula
CH,0 can have two structures namely ethyl alcohol and diethyl ether.
H
H
Н.
H
I
0-H
H
H
H
H
H н
H
Common Name: Ethyl alcohol
IUPAC: Ethanol
Common Name: Methoxymethane
IUPAC: Dimethyl ether
Cis and Trans Isomerism. In ethane CH3-CH3, both carbon atoms are sp hybridized
and tetrahedral. We can draw many structures for ethane, differing only in how one
methyl group is twisted in relation to the other. Such structures, differing only in rotations
about a single bond, are called conformations.
The double bonds in alkenes do not allow free rotation; for example, 2-butene is quite
rigid. Because double bonds are rigid, we can separate and isolate compounds that differ
only in how their substituents are arranged on a double bond. 2-butene molecules with
the two methyl groups on the same side of the double bond is called cis-2-butene, and the
one with 2-methyl groups on the opposite side is called trans-2-butene.
H3C
CH3
H3C
H Н.
H н
H
H н
CH3
cis-2-butene
trans-2-butene
Cis-trans isomerism in cycloalkanes. Alkenes have rigid double bonds that prevent
rotation, giving rise to cis and trans isomers. Cycloalkanes are similar to alkenes in this
respect. Free rotation is not possible in cyclic or ring structures. A cycloalkane has two
distinct faces. If two substituents point toward the same face, they are cis. If they point
toward the opposite face they are trans. The following figure compares the cis and trans
isomers of 2-butene with 1,2-dimethylcyclopentane.
H3C
CH3
H3C
H
H Н
H
H н
CH3
Cis-2-butene
trans-2-butene
Н”
H3C
*H
CH3
нс”
CHE
cis-1,2-dimethylcyclopentane
trans-1,2-dimethylcyclopentane
Stereochemistry of Alkanes. Build a model for methane.
H
-H
H
H Н
H
Three-dimensional model
model
perspective drawing
imaginary flat
Now build a model of ethane. The two-methyl groups are not fixed in a single position
but are relatively free to rotate about a single bond connecting the two carbon atoms. The
different arrangements formed by the rotation about a single bond are called
conformations, and specific conformation is called a conformer.
H
H
H Н
H
H
Perspective drawing
Model viewed along carbon-carbon bond
1) Draw below eclipsed and staggered conformations of ethane in Newman projection.
Eclipsed
Staggered
Build a model of an alkane from ethane by joining one more carbon atom to form a
three-carbon chain. 2) What is the name of this hydrocarbon? 3) Could a branched chain
containing only three carbon atoms be formed?
H
H
Н.
H
CH
H н
H
Perspective drawing
Three-dimensional model
25
4) Draw below eclipsed and staggered conformations of the above compound in Newman
projection.
5) Join four carbon atoms together by single bonds. Is it possible to do this in more than
one way? Add hydrogen atoms to all the unused valences of carbon atoms. 6) What is
the molecular formula of the hydrocarbon molecule? 7) What are the common names
and IUPAC names of the isomers? 8) Draw the structural formulas of these compounds.
9) Draw different conformations (Newman projection) of straight chain containing
four-carbon alkane.
10) By using models, construct all the isomers of pentane C3H12. Draw their structural
formulas and give their common and IUPAC names.
11) Construct models of possible dichloroethanes, molecular formula C2H4Cl2.
Draw their structural formulas and name them.
12) Construct all the isomers of hexane, CH 4. Draw their structural formulas and name
them.
Conformation of Cyclohexane: Cyclohexane achieves tetrahedral bond angles and
staggered conformations by assuming a puckered conformation. The most stable
conformation is the chair conformation. Generally, any pair of tetrahedral atoms attached
to each other tends to have their bonds staggered. Any deviation from the staggered
positions is accompanied by torsional strain.
The staggered chair conformation of cyclohexane is similar to staggered conformation of
ethane.
H
H
H
H
CH2
H
H
H
HT
CH2
H Н
H
H
н
H
Staggered
Newman projection of cyclohexane
Staggered
Newman projection of ethane
28
Boat conformation of cyclohexane is similar to eclipsed conformation of ethane.
3.0 kcal/mole
1.0 kcal/mole
Eclipsed
Newman projection of cyclohexane
Eclipsed
Newman projection of ethane
Cyclohexane in chair shape
The following Figure shows the Chair-chair interconversion of cyclohexane from one
chair to the other chair via boat conformation.
Flagpole hydrogens
H
H
H
H
H
H
-H
H
H
HVH
Н.
CH
H
” H
H
H
H
H
Chair-chair interconversion of methyl cyclohexane from one chair to the other chair via
boat conformation is shown below. The methyl group in the left chair is axial, and eq
29
43
uatorial in the right chair (ring flip).
Flagpole interaction
CH3
H
H н
H
H
H
H
HVH
H
H
H
CH3
H
H
H
H
Lab Report: Write down the entire experiment in the lab notebook by completing the
required sections. You will be graded from the lab notebook.
EXPERIMENT 4
Reactions of Hydrocarbons and Proton Nuclear
Magnetic Resonance Experiment (‘H NMR)
Objective
Perform qualitative tests to distinguish alkanes, alkenes, alkynes, and aromatic
hydrocarbons.
Introduction
In this experiment students will perform qualitative tests to distinguish alkanes,
alkenes, alkynes, and aromatic hydrocarbons from one another. Students will run proton
NMR experiment for different organic compounds.
Alkanes are saturated hydrocarbons containing all single bonds and sp hybridization.
Alkenes (sp?) and alkynes (sp) are unsaturated hydrocarbons that consist of double and
triple bonds respectively. Aromatic hydrocarbons contain ring structures with alternate
single and double bonds (sp?). Aromatic compounds behave differently from alkenes and
alkynes because aromatic compounds have delocalization of pi-electrons, where as
alkenes and alkynes have localized double and triple bonds. Different types of hydrogens
are shown below.
aromatic
acetylenic
benzylic
H
Н
10
H
H н
H-CEC
C-H
H
H
H
20
aromatic
Vinylic
allylic
Vinylic
Hydrocarbons-Alkanes (Saturated hydrocarbons).
Alkanes are in the least reactive class of hydrocarbons. Alkanes do not react with
strong acids, bases or most other reagents. The low reactivity is due to lack of affinity for
other reagents and therefore they are called “paraffins”. In Latin,” paraffin” means too
little affinity towards other reagents. Alkanes are quite inert and therefore they are not
usually characterized chemically. Instead they are characterized by using spectroscopy
(IR, NMR, etc.).
Hydrocarbons undergo free-radical chain bromination through the mechanism shown
below.
Chain Initiation
Br Br
Br.
Br.
Chain Propagation
Br.
R+
H-Br
R1
R-Br+ Br.
Chain Termination
R.
+
Br.
R—Br
R:
+
R.
R-R
Br.
Br.
Br-Br
R = alkyl (methyl, ethyl, etc; cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc.)
Hydrocarbons-Alkenes (Unsaturated hydrocarbons).
The carbon-carbon double bond of alkenes (olefins) can be detected very easily by
chemical tests. Alkenes undergo addition reactions across carbon-carbon double bond by
ionic process to give saturated compounds. The reaction of alkenes with bromine solution
is shown below.
Br
i
Alkene
Br
1,2-dibromoalkane
colorless
Alkenes are oxidized to 1,2-diols with potassium permanganate, with the reduction of
manganese +7, which is purple, to +4, which is brown.
3
C
C
+ 2 KMnO4 +41,0
+ 2MnO2 (s) + 2KOH
OH
OH
alkene
purple
1,2-diol
brown
Hydrocarbons-Alkynes: (Unsaturated hydrocarbons)
Alkynes give a positive test with bromine solution as well as with potassium
permanganate solution. Bromine adds to the carbon-carbon triple bond, with the
disappearance of red color. Potassium permanganate oxidizes alkynes to carboxylic acids,
concurrently with the reduction of the manganese from +7 to +4, a brown color.
Br
Br Br
-CEC-
+ Br2
Br
-C-C-
Br Br
colorless
alkyne
red
R-C=C-R’ + 2KMnO4 + 2H20
dort lor
R
+ 2H2O + 2MnO2
You are not performing the tests for identification of alkynes (ethyne or acetylene) in the
lab. Terminal alkynes react with sodium or cuprous ammonium chloride to liberate
hydrogen gas and form a salt.
H-C=C-H + 2Na
Nat CSC Na
Cut CBC Cut
H-C=C-H + Cut NH3C1
Cuprous ammonium chloride
Hydrocarbons-Aromatic
Aromatic Hydrocarbons burns with sooty flame. Fuming sulfuric acid converts
aromatic compounds to aryl sulfonic acids. A positive test for the presence of aromatic
ring is complete dissolution of the aromatic compound, evolution of heat and minimum
charring.
-Н
+
H2SO4 +
SO3
-SO3H
Experimental procedure
The following four tests will be performed on cyclohexane (alkane), cyclohexene
(alkene), acetylene or ethyne (alkyne), and toluene or methylbenzene (aromatic). Record
your observations in the Table 4.1.
1. Bromine Test. In a test tube place 5 drops of the hydrocarbon compound (unknown)
to be tested and add drop-wise with shaking bromine in chloroform (Br2 in CHC13)
solution. Record the number of drops added to retain the red-brown color of bromine
solution. As you add the bromine solution to some hydrocarbons (alkenes and alkynes)
the red-brown color of bromine solution disappears (decolorizes), and later on the brown-
red color persists. If the solution has not been decolorized, prepare a second test tube
with 5 drops of hydrocarbon and the same number of drops of bromine solution and place
it in the sunlight or provided light source. Compare test tubes after ten minutes. Pay
special attention to color of the second test tube. Did the color of the bromine disappear?
If brown-red color of bromine disappears (or discharged) and hydrogen bromide evolved,
then substitution has occurred. Hydrogen bromide (HBr) gas can be detected by placing
moistened blue litmus paper across the mouth of the test tube and noting whether it turns
red, indicating the presence of an acidic gas
Table 4.1 Classification tests for hydrocarbons
Reagent Cyclohexane
(alkane)
Toluene (aromatic)
Cyclohexene
(alkene)
1. Bromine in CHCI:
2. Bromine in CHCl3
Not necessary to
perform this test for
alkenes because
alkenes react readily
at room temperature
and they do not
require light
light
3. Permanganate
solution
4. Concentrated
sulfuric acid
(this test is not
conclusive)
EXPERIMENT 4
Reactions of Hydrocarbons and Proton Nuclear
Magnetic Resonance Experiment (‘H NMR)
Objective
Perform qualitative tests to distinguish alkanes, alkenes, alkynes, and aromatic
hydrocarbons.
Introduction
In this experiment students will perform qualitative tests to distinguish alkanes,
alkenes, alkynes, and aromatic hydrocarbons from one another. Students will run proton
NMR experiment for different organic compounds.
Alkanes are saturated hydrocarbons containing all single bonds and sp hybridization.
Alkenes (sp?) and alkynes (sp) are unsaturated hydrocarbons that consist of double and
triple bonds respectively. Aromatic hydrocarbons contain ring structures with alternate
single and double bonds (sp?). Aromatic compounds behave differently from alkenes and
alkynes because aromatic compounds have delocalization of pi-electrons, where as
alkenes and alkynes have localized double and triple bonds. Different types of hydrogens
are shown below.
aromatic
acetylenic
benzylic
H
Н
10
H
H н
H-CEC
C-H
H
H
H
20
aromatic
Vinylic
allylic
Vinylic
Hydrocarbons-Alkanes (Saturated hydrocarbons).
Alkanes are in the least reactive class of hydrocarbons. Alkanes do not react with
strong acids, bases or most other reagents. The low reactivity is due to lack of affinity for
other reagents and therefore they are called “paraffins”. In Latin,” paraffin” means too
little affinity towards other reagents. Alkanes are quite inert and therefore they are not
usually characterized chemically. Instead they are characterized by using spectroscopy
(IR, NMR, etc.).
Hydrocarbons undergo free-radical chain bromination through the mechanism shown
below.
Chain Initiation
Br Br
Br.
Br.
Chain Propagation
Br.
R+
H-Br
R1
R-Br+ Br.
Chain Termination
R.
+
Br.
R—Br
R:
+
R.
R-R
Br.
Br.
Br-Br
R = alkyl (methyl, ethyl, etc; cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc.)
Hydrocarbons-Alkenes (Unsaturated hydrocarbons).
The carbon-carbon double bond of alkenes (olefins) can be detected very easily by
chemical tests. Alkenes undergo addition reactions across carbon-carbon double bond by
ionic process to give saturated compounds. The reaction of alkenes with bromine solution
is shown below.
Br
i
Alkene
Br
1,2-dibromoalkane
colorless
Alkenes are oxidized to 1,2-diols with potassium permanganate, with the reduction of
manganese +7, which is purple, to +4, which is brown.
3
C
C
+ 2 KMnO4 +41,0
+ 2MnO2 (s) + 2KOH
OH
OH
alkene
purple
1,2-diol
brown
Hydrocarbons-Alkynes: (Unsaturated hydrocarbons)
Alkynes give a positive test with bromine solution as well as with potassium
permanganate solution. Bromine adds to the carbon-carbon triple bond, with the
disappearance of red color. Potassium permanganate oxidizes alkynes to carboxylic acids,
concurrently with the reduction of the manganese from +7 to +4, a brown color.
Br
Br Br
-CEC-
+ Br2
Br
-C-C-
Br Br
colorless
alkyne
red
R-C=C-R’ + 2KMnO4 + 2H20
dort lor
R
+ 2H2O + 2MnO2
You are not performing the tests for identification of alkynes (ethyne or acetylene) in the
lab. Terminal alkynes react with sodium or cuprous ammonium chloride to liberate
hydrogen gas and form a salt.
H-C=C-H + 2Na
Nat CSC Na
Cut CBC Cut
H-C=C-H + Cut NH3C1
Cuprous ammonium chloride
Hydrocarbons-Aromatic
Aromatic Hydrocarbons burns with sooty flame. Fuming sulfuric acid converts
aromatic compounds to aryl sulfonic acids. A positive test for the presence of aromatic
ring is complete dissolution of the aromatic compound, evolution of heat and minimum
charring.
-Н
+
H2SO4 +
SO3
-SO3H
Experimental procedure
The following four tests will be performed on cyclohexane (alkane), cyclohexene
(alkene), acetylene or ethyne (alkyne), and toluene or methylbenzene (aromatic). Record
your observations in the Table 4.1.
1. Bromine Test. In a test tube place 5 drops of the hydrocarbon compound (unknown)
to be tested and add drop-wise with shaking bromine in chloroform (Br2 in CHC13)
solution. Record the number of drops added to retain the red-brown color of bromine
solution. As you add the bromine solution to some hydrocarbons (alkenes and alkynes)
the red-brown color of bromine solution disappears (decolorizes), and later on the brown-
red color persists. If the solution has not been decolorized, prepare a second test tube
with 5 drops of hydrocarbon and the same number of drops of bromine solution and place
it in the sunlight or provided light source. Compare test tubes after ten minutes. Pay
special attention to color of the second test tube. Did the color of the bromine disappear?
If brown-red color of bromine disappears (or discharged) and hydrogen bromide evolved,
then substitution has occurred. Hydrogen bromide (HBr) gas can be detected by placing
moistened blue litmus paper across the mouth of the test tube and noting whether it turns
red, indicating the presence of an acidic gas
Table 4.1 Classification tests for hydrocarbons
Reagent Cyclohexane
(alkane)
Toluene (aromatic)
Cyclohexene
(alkene)
1. Bromine in CHCI:
2. Bromine in CHCl3
Not necessary to
perform this test for
alkenes because
alkenes react readily
at room temperature
and they do not
require light
light
3. Permanganate
solution
4. Concentrated
sulfuric acid
(this test is not
conclusive)
2. Potassium Permanganate Test (Baeyer’s Test). To a test tube, add 5 drops of the
hydrocarbon compound (unknown to be tested). Add drop-wise, with vigorous shaking,
an aqueous solution of 0.5% potassium permanganate and 5% sodium carbonate. Record
the number of drops needed to develop the persistent purple color. The disappearance of
purple color and the formation of a brown suspension, which is manganese (II) dioxide,
at the bottom of the test tube is a positive indication for a carbon-carbon double or triple
bond (unsaturation).
Caution: Be careful in handling concentrated sulfuric acid.
3. Sulfuric acid test. In a clean dry test tube place 5 drops of hydrocarbon (unknown)
compound to be tested. Cautiously add drop-wise approximately 1.5 mL of 98% sulfuric
acid, accompanied by a gentle shaking, and then allow it to stand for a few minutes. A
positive test for the presence of an aromatic ring is complete dissolution of the
compound, evolution of heat (hold test tube in your hand), and minimal charring.
4. Cuprous Ammonium Chloride Test. Add 3.0 mL of cuprous ammonium chloride
solution to acetylene (ethyne). The copper derivative thus formed is collected by filtration
using either Buchner funnel or Hirsch funnel with suction. Dry the precipitate in air not in
oven. You should note a “popping” sound due to small explosion of the cuprous
acetylide.
Acetylene gas is prepared by reacting calcium carbide by slow addition of water.
Acetylene gas (ethyne) is collected by displacement of water. The laboratory technician
will do the preparation in hood.
Nuclear Magnetic Resonance Experiment (‘H NMR)
NMR is a powerful instrument to determine the structure of organic compounds. During this lab
you will use the NMR spectrometer to determine the structures of phenyl acetylene/cinnamic
acid/aspirin/benzoic acid and acetanilide. In this lab you will run proton NMR (‘H NMR)
experiment and determine the different types of hydrogens present in the organic compounds.
The structures of the five compounds are shown below.
OH
ch
OH
Acetanilide
CHE
Aspirin
Phenylacetylene Benzoic acid (Acetyl salicylic acid) Cinnamic acid
Place about 5 mg of the compound using a clean microspatula in a clean vial and add about
1.5 mL of CDCIz that contains a standard TetraMethyl Silane (TMS) whose chemical shift (8)
value is zero. Transfer the solution to an NMR tube using a clean glass pipet and run the NMR
spectrometer in Room S328. NMR manual is kept in the NMR room. Follow the instructions in
the manual how to run the NMR spectrometer. From the spectrum you will determine different
types of hydrogens present in the organic compound. Interpretation of proton NMR
spectrum:
1. Chemical shift (8) values will give the different type of hydrogens: aliphatic, aromatic,
vinylic (alkene), and acetylenic (alkyne) present in the compound and compare the values
in the Table 1.
2. Integration of each signal or peak gives information about how many hydrogens present
in each type.
3. Spin-spin splitting gives information about other nearby hydrogens. Applying (N+1) rule
where N is number of neighboring hydrogens.
Table 1 Typical proton Chemical Shift (8) values
Type of proton
Approximate (8) Type of proton Approximate (8)
alkane (-CH3)
1.0
R-CHO 9-10
5-6
R-COOH
10-12
alkene
*
H
alkyne
-H
2.5
R-OH
2-5
2.1
Yous
R-CH2-X (X = halogen, O) 3-4
R-NH2
4-7
Benzene (Ph = phenyl)
7.2
Ph-CH
2.3
EXPERIMENT 4
Lab Report
Title of experiment
Objective
Results
Table 4.1 Classification tests for hydrocarbons
Reagent Cyclohexane
(alkane)
Bromine in CHCI:
Cyclohexene
(alkene)
Toluene
(aromatic)
Bromine in CHCl3 +
light
Not necessary to
perform this test for
alkenes because
alkenes react readily at
room temperature and
they do not require
light.
Permanganate
solution
Concentrated
sulfuric acid
Conclusions (one or two sentences only)
Post Laboratory questions
1. What test/s could be used to distinguish between 2-hexene and n- hexane?
2. Draw the structures of the following compounds and indicate the hybridization at
the between the carbon-carbon single, double and triple bonds.
1-propene, propane, and propyne.
3. Arrange the following compounds in the order of increasing acidity.
2-pentene, n-pentane, and 2-pentyne.
4. Comment on the green chemistry of this experiment. That is, the nature and amount of
solvent (for example water, etc.), and atom economy (number of atoms in the reactants
versus products) in this experiment.
Among the following compounds which compound is least stable and Why? Give two reasons?
Cyclopentane, cyclobutane, cyclopropane, cyclohexane
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Arrange the following carbocations in the order of increasing stability.
The substituents are in the parenthesis.
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(CH3CH2)2CH, CH3CH2, (CH3CH2)3c7, (CH3CH2CH2
Two chair conformation possible for trans-1,3-dimethylcyclohexane. Which chair
conformation is more stable and why?
Two chair conformation possible for trans-1,4-dimethylcyclohexane. Which chair
conformation is more stable and why?
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How many geometrical isomers (cis and trans) are possible for 1,2-dimethylcyclopentane and name them?
What is the highest energy conformation in butane? What are the two reasons for the highest energy?
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