Question

Question: For each of the compounds described by the following names,

1. draw a three-dimensional representation

2. star (*) each chiral center

3. draw any planes of symmetry.

4. draw any enantiomer.

5. draw any diastereomers.

6. label each structure you have drawn as chiral or achiral

(a) (S)-2-chlorobutane

(b)(R)-1,1,2-trimethylcyclohexane

(c) (2R,3S)-2,3-dibromohexane

(d) (1R,2R)-1,2-dibromocyclohexane

(e) meso-hexane-3,4-diol,CH₃CH₂CH(OH)CH(OH)CH₂ CH₃

(f) $\left(\pm \right)$-hexane-3,4-diol

Short answer

Answer

(a) chiral

(b) chiral

(c) chiral

(d) chiral

(e) achiral

(f) achiral and chiral

Step-by-step solution

Chiral molecule

Molecules having exact mirror images of itself and has non- super imposable mirror image is known as a chiral molecule. Enantiomers or optical isomers are two mirror images of a chiral molecule. Any compound that is chiral must have an enantiomer.

Achiral molecule

Achiral molecules are superimposable with their mirror images. Any compound that is achiral cannot have an enantiomer.

Meso compounds

Meso compounds are defined as those which contain two or more asymmetric centres that are optically inactive. They consist of internal plane of symmetry such that one half of the molecule forms the mirror image of the other half. Since the optical activity due to one half is counterbalanced by the optical activity of the other half, so meso compounds are optically inactive. In general, it can be said that a meso compound is an achiral compound that has chiral centers (asymmetric carbons).

Explanation

The asymmetric carbon is shown by star (*) in each structure.

(a) This is a chiral compound since it gives a different or non-superimposable mirror image to that of the original compound. The central carbon has four different groups attatched to it.

chiral

(b) This is a chiral compound since it gives a different or non-superimposable mirror image to that of the original compound.

chiral

(c) This is a chiral compound since it gives a different or non-superimposable mirror image to that of the original compound

chiral

(d) This is a chiral compound since it gives a different or non-superimposable mirror image to that of the original compound

chiral

(e) This is an achiral compound since it has plane of symmetry (meso compound).

achiral

(f) For , both achiral (having plane of symmetry) and chiral structures can be drawn.

achiral chiral

4. Enantiomers (mirror images) that can be drawn are shown below.

enantiomers

5. Diastereomers (not mirror images) can be drawn for the compounds (c), (d) and (e) only.

diastereomers