How may `2,3,4,5`-terahydroxyadipic acids are possible?

Options

A. Eight
B. Six
C. Ten
D. Four

Answer

C

Explanation

`HOOCoverset(**)CH(OH)overset(**)CH(OH)overset(**)CH(OH)overset(**)CH(OH)COOH`
There are four chiral carbon atoms but two pairs are similar. Therefore ten (instead of `2^(4) = 16`) steroisomers are possible as some steroisomers are meso compounds. The following are enantiomeric pairs: `R R R R` and `S S S S,R R R s` and `SSSR, R R SR` and `SSRS,RSSR` and `SR RS`. On the other hand, `RSRS` and `R RSS` are two different meso diasteromers because teh top and bottom halves have mirror imgaes.