Question

Total number of compounds with molecular formula C4H8O2, which can reduce both Tollen's reagent and PCC is

Answer 1

5

Answer 2

A compound that reduces Tollens’ reagent must have a free –CHO group, and one that is oxidized by PCC must have an –OH group (primary or secondary). Thus the compound must be a hydroxy aldehyde. For a 4‐carbon chain (with DBE = 1 provided by the carbonyl), if we always fix the aldehyde at C1 then the –OH group can be attached at C2, C3 or C4.

1. When –OH is at C2:

   Structure: CHO–CHOH–CH₂–CH₃

   This molecule has one chiral center (at C2) → exists as 2 enantiomers.

2. When –OH is at C3:

   Structure: CHO–CH₂–CHOH–CH₃

   This also gives one chiral center (at C3) → 2 enantiomers.

3. When –OH is at C4:

   Structure: CHO–CH₂–CH₂–CH₂OH

   This molecule has no chiral centre (achiral).

Counting all stereoisomers:

Total = 2 (from C2–OH) + 2 (from C3–OH) + 1 (from C4–OH) = 5 compounds.