Question

The product which is not formed in the following reaction:

     CH3          CH3
     |            |
Ph-C-CH-CH-CH-CH2OH
     |   |   |
    OH OH OH

$\xrightarrow{HIO_4 \text{ (excess)}}$

• A. HCOOH
• B.

         CH3
         |
  Ph-C-CH3
     ||
     O
  

• C.

    CH3
    |
  OHC-CH-CH2OH
  

• D.

    CH3
    |
  OHC-CH-CHO.
  

Answer 1

Answer: (C), (D)

C and D

Answer 2

The reaction involves the oxidation of a polyol with periodic acid ($HIO_4$) in excess. Periodic acid cleaves carbon-carbon bonds between adjacent carbons bearing hydroxyl groups (vicinal diols).

The given substrate has hydroxyl groups on carbons $C_1, C_2, C_3, C_4,$ and $C_5$, where: $C_1$: Ph-C(OH)(CH3)- $C_2$: -CH(OH)- $C_3$: -CH(OH)- $C_4$: -CH(OH)- $C_5$: -CH2OH

The vicinal diol cleavages occur at the bonds: $C_1-C_2$, $C_2-C_3$, $C_3-C_4$, and $C_4-C_5$.

Upon cleavage and oxidation:

• A tertiary alcohol (like $C_1$) becomes a ketone. The fragment from $C_1$ is Ph-C(=O)-CH3 (Acetophenone). This matches Option (B).
• A secondary alcohol (like $C_2, C_3, C_4$) becomes an aldehyde (-CHO).
• A primary alcohol (like $C_5$) becomes formic acid (HCOOH). This matches Option (A).

The CH3 group is attached to $C_1$. Since $C_1$ is oxidized to a ketone (Acetophenone), the CH3 group remains attached to this ketone.

Options (C) and (D) depict fragments containing a CH(CH3) unit where the CH is part of an aldehyde. This is not possible because the CH3 group is exclusively on $C_1$, which forms acetophenone and does not become an aldehyde fragment. Therefore, products (C) and (D) are not formed.