Question

Reaction of benzyl magnesium chloride with formaldehyde yields alcohols N and P after protonation. Draw a stepwise mechanism that shows how both products are formed.

Short answer

Grignard reagents are organomagnesium halide compounds of the form R-MgX where R can be any alkyl or aryl group. Grignard reagents react with aldehydes and ketones to give primary, secondary or tertiary alcohols.

The general reaction scheme is given below:

Reaction of Grignard reagent with carbonyl compounds

Step-by-step solution

Reaction of Grignard reagent with carbonyl compounds

Grignard reagents are organomagnesium halide compounds of the form R-MgX where R can be any alkyl or aryl group. Grignard reagents react with aldehydes and ketones to give primary, secondary or tertiary alcohols.

The general reaction scheme is given below:

Reaction of Grignard reagent with carbonyl compounds

Mechanism for formation of product P

The carbon atom attached to the MgX group carries a partial negative charge according to the Umpolung chemistry of the compound. Thus, this negative charge attacks the electrophilic carbon center of the carbonyl group. The mechanism is shown below:

Mechanism for formation of product P

Mechanism for formation of product N

The carbon atom attached to the MgX group participates in resonance with the benzene ring, and instead of the negative charge, the double bond attacks the carbonyl carbon center. The mechanism is given below:

Mechanism for formation of product N