Consider all possible isomeric ketones, including stereoisomers, of MW = 100. All these isomers are independently reacted with (NOTE: stereoisomers are also reacted separately). The total number of ketones that give a racemic product(s) is/are
← JEE Advanced 2014 · Paper 1
ChemistryInteger+3Question 31 of 60
JEE Advanced 2014 · Paper 1, Chemistry question 31
Answer and worked solution
Official answer: 5
Ketones of MW 100 are :
| Ketone | Product of NaBH₄ |
|---|---|
| hexan-2-one | new stereocentre, racemic |
| hexan-3-one | racemic |
| 4-methylpentan-2-one | racemic |
| 2-methylpentan-3-one | racemic |
| 3,3-dimethylbutan-2-one | racemic |
| (R)-3-methylpentan-2-one | two diastereomers, not racemic |
| (S)-3-methylpentan-2-one | two diastereomers, not racemic |
The five achiral ketones give a new stereocentre with equal attack from both faces, so their products are racemic. The two enantiomers of 3-methylpentan-2-one already have a stereocentre, so each gives an unequal mixture of diastereomers.
Answer: 5