Isoprene (2-methylbuta-1,3-diene) is treated with 1 mol of HCl at low temperature under kinetic control. Assume that the allylic cation is captured by chloride at the terminal carbon bearing the greater positive charge. The major product is

A3-chloro-3-methylbut-1-ene
B4-chloro-2-methylbut-1-ene
C1-chloro-3-methylbut-2-ene
D3-chloro-2-methylbut-1-ene

Answer: A

Protonation of C-1 (the terminal

CH X_{2}

next to the methyl-bearing carbon) gives the tertiary allylic cation

(CH X_{3}) X_{2} C X^{+} - CH = CH X_{2}

, more stable than the secondary allylic cation from protonation at C-4. Its positive charge is larger at the tertiary carbon, so kinetic attack there gives the 1,2-adduct

(CH X_{3}) X_{2} CCl - CH = CH X_{2}

. The 1,4-adduct 1-chloro-3-methylbut-2-ene is the thermodynamic product.

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Isoprene (2-methylbuta-1,3-diene) is treated with 1 mol of HCl at low temperature under kinetic control. Assume that the allylic cation is captured by chloride at the terminal carbon bearing the greater positive charge. The major product is

Answer: A

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