Question

For which of the following choice(s), erythro and threo designation can be used?
(a)-

(b)-

(c)-

(d)-

Answer 1

Erythro and threo are two configurations in which molecules are written when the molecules have a chiral carbon atom. Erythro is the configuration when the same groups are on the same side of the carbon atom and Threo is the configuration when the same groups are on the opposite side of the carbon atom.

Complete answer:
In organic compounds, there are many configurations in which we can distinguish the molecule having the same molecular formula but the arrangement of the molecules are different.
Erythro and threo are two configurations in which molecules are written when the molecules have a chiral carbon atom. Erythro is the configuration when the same groups are on the same side of the carbon atom and Threo is the configuration when the same groups are on the opposite side of the carbon atom.
In option (b) and option (c), both the substituents on the carbon atom number 2 and 3 are the same and both the carbon atoms are chiral, i.e., all the substituent groups on the carbon atom are different.
The compound in option (b) is:

The erythro and the threo form are given below:

The compound in option (c) is:

The erythro and the threo form are given below:

Therefore, the correct answers for this question are options (b) and (c).

Note:
In the same way as the erythro and threo are distinguished, we have syn and anti configuration can be written, in sync the same groups are written on the same side while in anti the same groups are written on the opposite side.