The halide shown is treated separately with sodium ethoxide in ethanol (I) and with potassium tert-butoxide in tert-butanol (II). Which pair gives the major alkene in I and in II respectively?

AI: 2,3-dimethylbut-2-ene; II: 2,3-dimethylbut-1-ene
BI: 2,3-dimethylbut-2-ene; II: 2,3-dimethylbut-2-ene
CI: 3,3-dimethylbut-1-ene; II: 2,3-dimethylbut-1-ene
DI: 2,3-dimethylbut-1-ene; II: 2,3-dimethylbut-2-ene

Answer: A

The compound is 2-bromo-2,3-dimethylbutane. Ethoxide gives the Saytzeff alkene, the tetrasubstituted 2,3-dimethylbut-2-ene, by removing the tertiary C-3 hydrogen. The bulky tert-butoxide attacks the unhindered methyl hydrogens, giving the Hofmann alkene 2,3-dimethylbut-1-ene. 3,3-Dimethylbut-1-ene would need a skeleton change.

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The halide shown is treated separately with sodium ethoxide in ethanol (I) and with potassium tert-butoxide in tert-butanol (II). Which pair gives the major alkene in I and in II respectively?

Answer: A

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