Concept explainers
Interpretation:
The factor behind the observation that tertiary alcohols react faster with HX than secondary alcohols and the factor behind the observation that methanol reacts with HX faster than primary alcohols, are to be explained.
Concept introduction:
Electrophiles are electron deficient species that have positive or partially positive charge. Lewis acids are electrophiles that accept electron pair.
Nucleophiles are electron rich species that have negative or partially negative charge. Lewis bases are nucleophiles that donate electron pair.
Substitution reaction: A reaction in which one of the hydrogen atoms of a hydrocarbon or a functional group is substituted by any other functional group is called substitution reaction.
Nucleophilic substitution reaction is a reaction in which an electron rich nucleophile attacks the positive or partial positive charge of an atom or a group of atoms to replace a leaving group.
The
The
An
The nucleophilic substitutions in which a nucleophile replaces a leaving group are known as
The stability of carbocation:
Reaction of tertiary and secondary alcohols with HX proceeds via SN1 pathway. In SN1, the formation of carbocation is the rate determining step. Tertiary alcohols form more stable carbocation than secondary alcohols, and therefore, reacts faster with HX.
For primary alcohols and methanol, the reaction with HX proceeds via SN2 pathway. The backside attack of the nucleophile and simultaneous departure of the leaving group is the rate determining step here. The primary alcohol being more crowded than methanol reacts slower with HX compared to methanol.
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ORGANIC CHEM. VOL.1+2-W/WILEYPLUS
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