The substitution reaction of an alkyl halide mainly occurs by the SN1 or SN2 mechanism. Whatever mechanism alkyl halides follow for the substitution reaction to occur, the polarity of the carbon-halogen bond is responsible for these substitution reactions. The rate of SN1 reactions is governed by the stability of the carbocation, whereas for SN2 reactions the steric factor is the deciding factor. If the starting material is a chiral compound, we may end up with an inverted product or a racemic mixture depending upon the type of mechanism followed by the alkyl halide. Cleavage of ethers with HI is also governed by the steric factor and the stability of the carbocation, which indicates that in organic chemistry these two major factors help us in deciding the kind of product formed.
Predict the major product formed when 2-bromopentane reacts with alcoholic KOH.
Predict the major product formed when 2-bromopentane reacts with alcoholic KOH.
Answer: Pent-2-ene (Saytzeff product), CH₃CH=CHCH₂CH₃.
Solution
Alcoholic KOH causes dehydrohalogenation (β-elimination). By Saytzeff's rule the more substituted alkene dominates:
(pent-1-ene is the minor product).
(pent-1-ene is the minor product).
CBSE Class 12 Board · 2020 · Subjective