Under ionising conditions (aqueous formic acid), which of the following benzyl chlorides $X - C X_{6} H X_{4} - CH X_{2} - Cl$ undergoes SN1 solvolysis fastest?

A $X = H$
B $X = 4-NO2$
C $X = 3-NO2$
D $X = 4-OCH3$

Answer: D

The rate-determining step forms a benzyl cation. A para-methoxy group stabilises it strongly by +M donation (the positive charge is delocalised onto oxygen), while nitro groups destabilise it by -M and -I effects. The 4-methoxybenzyl chloride therefore ionises fastest.

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Under ionising conditions (aqueous formic acid), which of the following benzyl chlorides X−CX6​HX4​−CHX2​−Cl undergoes SN1 solvolysis fastest?

Answer: D

More questions on SN1 vs SN2: substrate, nucleophile, solvent, leaving group

Under ionising conditions (aqueous formic acid), which of the following benzyl chlorides $X - C X_{6} H X_{4} - CH X_{2} - Cl$ undergoes SN1 solvolysis fastest?