Structures of Organic Molecules and Molecular Orbital Theory Questionnaire
1. How many chiral (asymmetric) C atoms are in the molecule below?A. 2
2. What is the correct formula of the molecule below?
3. How many π bonds are there in the molecule (E)-5-bromo-6-methylocta-1,3-dien-7-yne?
4. Which pair of the structures are isomers?
5. Which one of the following statements is correct?
A. Molecules with a π bond adjacent to a nitrogen atom will undergo fast interconversion between
resonance forms at room temperature.
B. The molecule (E)-4,6-dimethylhept-2-ene has 3 methyl groups in total.
C. All pure compounds that contain chiral carbon atoms are optically active.
D. The formula of spiro[4.5]decane is C10H18.
E. The molecules of tert-butylcyclohexane do NOT undergo ring-flip because the A-value of tertbutyl group is very large.
6. Assuming all the atoms follow the octet rule, add formal charges to the species below, and
select the total number of charges you added. Note each structure may have 0, 1 or multiple
A. 1 positive charge, 3 negative charges
B. 2 positive charges, 3 negative charges
C. 3 positive charges, 2 negative charges
D. 3 positive charges, 3 negative charges
E. 2 positive charges, 2 negative charges
7. What is the relationship between the two molecules below?
A. They are a pair of enantiomers.
B. They are two diastereomers.
C. They are conformers of the same molecule.
D. They are the same conformation of the same molecule, viewed from different angles.
E. They are cis-trans stereoisomers.
8. This molecular structure below is shared 8 stereoisomers because it has 3 asymmetric
carbon atoms. This is based on a rule proposed by which scientist?
A. Jacobos van’t Hoff
B. Gilbert Lewis
C. Friedrich Wöhler
D. Emil Fisher
E. Dmitri Mendeleev
Add one more methylene to the chain to make Version II, change -OH to -Cl to make Version III.
9. What is the degree of unsaturation of the molecule below:
10. Which one of the following Newman projections correctly depicts the lowest conformation of
the meso compound (2R,3S)-butane-2,3-diol? (hint: 3 of the choices are wrong conformers, 1 of
the choice is a wrong isomer)
Version II: change -OH to -Cl; Version III: change -OH to -Br. Don’t forget to change the compound
name in the problem text.
11. In their lowest energy conformations, are all the non-hydrogen atoms in the following
molecules in the same plane? Write “Yes” or “No” for each molecule [Do not add any other
text, including spaces, to your answer or it will be marked as incorrect.]. (1 pt each, 4 pts
12. Assign the configuration for the following carbon atoms where wedge and dash bonds are
drawn. Write R, S, or achiral for each molecule. [Do not add any other text, including
spaces, to your answer or it will be marked as incorrect.] (1 pt each, 4 pts total)
. (R, S, Achiral, S)
13. Which one of the following molecules is aromatic? (hint: consider their resonance structures)
[For carbonyl-containing molecules consider only the resonance forms that have a
formal charge on oxygen.]
14. Which one of the following molecule’s boiling point is irrelevant to hydrogen-bonding?
15. For the molecule below, write the number of sp3, sp2, and sp hybridized carbon atoms,
respectively. (note: this molecule has 19 carbon atoms in total) (1.5 pts each if one or two
correct answers, 4 pts total for three correct answers) [This 4 point scheme might be difficult
to realize in Canvas.]
sp hybridized carbon atoms. (7, 10, 2)
16. Which one of the following molecules does NOT have a molecular dipole?
17. Like carbon atoms, sp3 hybridized nitrogen atoms can be chiral. However, when nitrogen
atoms that have a pair of unshared electrons are attached to three different groups, the
pyramidal structure can undergo fast inversions at 1,000-100,000 times per second even at low
temperatures, as shown below. Therefore, these nitrogen atoms are not chirally stable
stereocenters and do not lead to optical activity of the molecules. In most context, a nitrogen
atom is considered a chiral center only if it is attached to four different groups as an ammonium
ion (like the case of an asymmetric carbon), or such inversion is prevented by conformational
strain (so the inversion does not happen or one structure has energetic advantage).
With the information above in mind, which one of the nitrogen atoms in the following structures
is a chiral center that can lead to optical activity?
18. With the A-value table at 298 K below, what is the free energy difference between the two
chair conformations of the molecule below at 298 K? (hint: absolute value for the “difference”,
do not worry about the positive/negative sign) (4 pts) [Consider making this multiple choice.
Students will want partial credit if they are close … you will be doing yourself a favor.]
. 0.7 kcal/mol
19. Which one of the bonds indicate by arrow in the molecule below have the longest bond
length? (hint: consider resonance structures when you determine bond orders)
20. Assuming the atoms follow the octet rule, how many unshared electron pairs need to be added
to the hypothetical structure shown to make it complete? How many positive formal charges need
to be added? How many negative formal charges need to be added?
A. 3 pairs, one positive charge, one negative charge
B. 4 pairs, one positive charge, no negative charge
C. 4 pairs, no positive charge, one negative charge
D. 3 pairs, one positive charge, no negative charge
E. 4 pairs, one positive charge, one negative charge
21. How many resonance contributors does this structure have? Include in your total only those
forms that have the same number of π bonds as the structure shown below. Also, do not
include the below structure itself, in your total. (Non-bonded/unshared valence electrons are
22. How are the compounds shown related?
A. They are enantiomers.
B. They are diastereomers.
C. They are constitutional isomers.
D. They are identical.
E. They are meso structures.
23. How should the compound shown be depicted as a Fischer projection? Select the option
that correctly indicates which functional groups (OH or H) correspond to the letters in the
A. R1 = R3 = H; R2 = R4 = OH
B. R1 = R3 = OH; R2 = R4 = H
C. R1 = R4 = OH; R2 = R3 = H
D. R1 = R4 = H; R2 = R3 = OH
E. R1 = R2 = R3 = R4 = OH
24. What is the lowest energy chair conformer for the compound shown? Select the option that
correctly indicates which functional groups would correspond to the letters in the template
A. R1 = R4 = H; R2 = tBu; R3 = Me
B. R1 = R3 = H; R2 = tBu; R4 = Me
C. R2 = R3 = H; R1 = tBu; R4 = Me
D. R2 = R4 = H; R1 = tBu; R3 = Me
E. R1 = R2 = H; R3 = tBu; R4 = Me
25. Convert the structure shown (right) to a Newman Projection. Select the option that correctly
indicates which functional groups would correspond to the letters in the template provided (left).
(hint: pick the correct depiction on the template. The structure shown with the template may not
correspond to the lowest energy conformer.)
A. R1 = R2 = H; R3 = SPh; R4 = tBu
B. R1 = SPh; R2 = R3 = H; R4 = tBu
C. R1 = SPh; R3 = tBu; R2 = R4 = H
D. R1 = R4 = H; R2 = tBu; R3 = SPh
E. R1 = SPh; R2 = tBu; R3 = R4 = H
How many carbon stereo centers are present in the compound below?
Rank the resonance contributors shown according to their importance (place the most important
Identify the relationship between the Newman projection and the 3D structure shown below.
How many spể hybridized carbons and how many 4º carbons are present in the molecule shown?
4 sp2 carbons and 5 4° carbons
6 sp2 carbons and 6 4º carbons
6 sp2 carbons and 6 4º carbons
6 sp2 carbons and 4 4° carbons
5 sp2 carbons and 2 4º carbons
Rank the following compounds by increasing H-X-H bond angles. (Smallest angle first.)
< 17 16 < 19 O 18 17 19 < 16 19 < 17 < 16 18 O 19 < 16 17 < 18 What are the formal charges in the Lewis structures given? : COC-N-Ph o=c=N_Ph E F F: 0-1; CO; N +1; G: 0-1; CO; N +1 F: +1; CO; N -1; G: 0-1; C +1; N O F: 0-1; C 0; N+1; F:00; C +1; N 0; O F: 0-1; C +1; N0; G: 0 -1; C 0; N +1 G: 0 0; C +1; N O G: 0 0; C +1; NO Which of the following molecules have a dipole moment? Br H HzC—0-CH H-C-H o-o- HzCN=C=NCH C1 H Br 6 CI 8 7 9 10 O 6,7, 10 0 6,8,10 6,7,8,9 O 6 only 7,8,9 Rank the following compounds in the order of increasing number of carbons with C-C-C bond angles of ~120°? (List the one with the fewest first.) 2 0 1,4, 5, 2, 3 0 4,2,5, 1,3 1,4,3,5,2 O 1,4,3,2,5 0 4,1,3,2,5 Rank the orbitals of 3-bromopropene in the order of increasing energies. n ls < T* a. b. 0* π * * 1s 1s 1s V V V V bbbbb V V V V V n V V V V V aa c. d. π A A A A A * 0 * n 0* i VVV T* e. Is < TT 71* O* с OOO b a The eight structures below show molecules of composition C4H6C1Br. How many different compounds are shown (counting pairs of enantiomers as 1 compound)? How many of these are optically active? CH Br Br CH CH Br HC CH ŠŅ HC HC 2 different compounds are shown; 1 of them is optically active. 4 different compounds are shown; 2 of them are optically active 4 different compounds are shown; 1 of them 1 optically active. 4 different compounds are shown; all 4 are optically active. O 2 different compounds are shown; 2 are optically active. What are the correct IUPAC names, left to right, for the ring systems shown? (The choices are given in the same order as the molecules are depicted, from left to right.) bicyclo[4.3.2]dodecane - spiro[4.5]decane - bicyclo[5.2.0]nonane bicyclo[6.5.4]dodecane - spiro[5.6.0]decane - bicyclo[5.2.0]nonane bicyclo[4.5.6]undecane - spiro[6.5.1]decane – bicyclo[7.4.2]nonane bicyclo[4.3.2]undecane - spiro[5.4]decane - bicyclo[5.2.O]nonane bicyclo[2.3.4]undecane - spiro[4.5]decane - bicyclo[7.4]nonane Using the Ingold- Cahn-Prelog rules, rank the four substituents shown from highest to lowest priority. CH-CH CH-CH: CH-CHBr2 -CC-CH CH=CE -HC=CH -CH=CE CH2-CH, Br CH-C1 CH2-C1 16 17 18 19 >
Identify the relationship between the constitutional isomers shown?
11 & 12 are positional, 12 & 13 are skeletal, 13 & 14 are functional isomers.
11& 12 are stereo-, 12 & 13 are positional, 13 & 14 are optical isomers.
O 11 & 12 are stereo-, 12 & 13 functional, 13 & 14 are skeletal isomers.
0 11 & 12 are positional, 12 & 13 are functional, 13 & 14 are skeletal isomers.
0 11 & 12 are functional 12 & 13 are positional, 13 & 14 are skeletal isomers.
The cyclohexane chair conformation with an axial CH3 group is 1.7 kcal/mol higher in energy
than the conformation with an equatorial CH3 group; an OCH3 group causes a difference of 0.6
kcal/mol between the two conformations. What is the energy difference between the two
conformations of trans-1-methoxy-3-methylcyclohexane?
How many isomers of octane have at least one 3° and at least one 4 carbon atom (in the same
How many hybridized C orbitals are present in the structure shown?
How many hybridized C orbitals are present in the structure shown?
Which of the following best describes the relationship of the structures shown?
They are geometric isomers
They are identical.
They are diastereomers
They are enantiomers
They are stereoisomers without a stereogenic center
Rank the following compounds by increasing strength of their intermolecular interactions with
1< 2 < 3 < 4 5 1< 2 < 3 < 5 < 4 ООООО 3< 1 < 2 < 4 - 5 3< 1 < 2 < 5 < 4 3< 1 < 2 < 4< 5 How many of the structures show the identical stereoisomer? CH3 H H ci CH; H ci *CH CH5 C1 Η нСІ CIH H C1 OOOOO 07