TAMU Acidic Hydrogen Atom at The Asymmetric Center of Enantiomerically Pure Questions
Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author)
Chapter 5 Homework: 33 to 40, 42, 44 to 46, 48, 51, 52, 54, 57, 58 and the following
problems:
1. Determine whether the following molecules are chiral:
Br
O
Cl
Br
Br
O
Br
Br
Me
Cl
Cl
Me
BH
(challenge)
CO2Me
O
Me
2. Determine the relationship between the following pairs of molecules: are they
the same molecule (possibly in a different conformation), enantiomers, or diastereomers?
Br
Cl
Cl
Br
Cl
Cl
CO2Me
Cl
Cl Cl
Cl
CO2Me
Cl Cl
CO2Me
Cl
Cl
CO2Me
Is cis-1,2-dichlorocyclohexane
chiral?
Chapter 5 Homework: 33 to 40, 42, 44 to 46, 48, 51, 52, 54, 57, 58 and the following
problems:
1. Determine whether the following molecules are chiral:
Br
O
Cl
Br
Br
O
Br
Br
Me
Cl
Cl
Me
BH
(challenge)
CO2Me
O
Me
2. Determine the relationship between the following pairs of molecules: are they
the same molecule (possibly in a different conformation), enantiomers, or diastereomers?
Br
Cl
Cl
Br
Cl
Cl
CO2Me
Cl
Cl Cl
Cl
CO2Me
Cl Cl
CO2Me
Cl
Cl
CO2Me
Is cis-1,2-dichlorocyclohexane
chiral?
1. From left to right, top to bottom: CHIRAL, ACHIRAL, CHIRAL, CHIRAL, ACHIRAL,
CHIRAL, ACHIRAL, CHIRAL, CHIRAL, CHIRAL.
2. From left to right, top to bottom: ENANTIOMERS, SAME MOLECULE,
DIASTEREOMERS, ENANTIOMERS, ENANTIOMERS (at low temperature) /
SAME MOLECULE (at room temperature)
Cl
chair flip
Cl
Cl
Cl
Cl
Cl
(rotate clockwise 120 degrees)
At low temperatures (150 K or lower), the cyclohexane chair flip is slow enough
that enantiomers of cis-1,2-dichlorocyclohexane can (in principle) be separated.
However, at room temperature (298 K), the two enantiomeric chair conformers
interconvert rapidly, making the molecule effectively achiral. When the chair
flip is rapid, the molecule can be treated as if it were flat:
Cl
(meso due to mirror plane)
Cl
On an exam, I will specify that the question should be answered on the basis of how a
molecule behaves under normal lab conditions (i.e., 298 K), if there is any ambiguity.