Organic Chemistry

Check each compound to see if it has the necessary requirements to have a stereoisomer

that is a meso compound. That is, does it have two asymmetric carbons with the same four

substituents attached to each of the asymmetric carbons?

Compounds A, E, and G do nothave a stereoisomer that is a meso compound because

they don’t have any asymmetric carbons.

Compounds C and H each have two asymmetric carbons. They do nothave a stereoisomer

that is a meso compound because each of the asymmetric carbons is notbonded to the

same four substituents.

Compounds B, D, and F have a stereoisomer that is a meso compound—they have two asym-

metric carbons and each asymmetric carbon is bonded to the same four atoms or groups.

The isomer that is the meso compound is the one with a plane of symmetry when an

acyclic compound is drawn in its eclipsed conformation (B), or when a cyclic compound is

drawn with a planar ring (D and F).

Now continue on to Problem 26.

PROBLEM 26

Which of the following compounds has a stereoisomer that is a meso compound?

a. 2,4-dibromohexane d. 1,3-dichlorocyclohexane

b. 2,4-dibromopentane e. 1,4-dichlorocyclohexane

c. 2,4-dimethylpentane f. 1,2-dichlorocyclobutane

PROBLEM 27 SOLVED

Which of the following are chiral?

H 3 C CH 3

H 3 C

CH 3 H 3 C

CH 3 Cl

H 3 C

CH 3

H 3 C

CH 3

H 3 C Cl Cl

Cl CH 3

Cl

Cl CH 3

H 3 C

CH 3

CH 3

HH

H 3 C

D F

H

CH 3

H

H 3 C

B

or

CH 2 CH 3

CH 2 CH 3

CH 3

H CH 3

H

CH 3 CH 2

H H

H 3 C

CH 2 CH 3

CH 3

C C

F

CH 3

CH 3

D

CH 3

CH 3

B

CH 3 CH 2 CHCHCH 2 CH 3

CH 3

CH 3

H

CH 3

Br

C

CH 3 CHCHCH 2 CH 3

CH 3

Br

G

CH 3 CH 2 CHCHCH 2 CH 3

CH 2 CH 3

CH 2 CH 3

E

CH 3

H 3 C

A

CH 3 CHCHCH 3

CH 3

CH 3

Section 5.10 Meso Compounds 203