Would 2-chloropropane or 1-chloro-2,2-dimethylpropane undergo substitution faster with $"HC≡C"^-"$ , $"Na"^+$ ?

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Answer 1 · 2014-12-20T18:24:52

2-Chloropropane will undergo substitution faster than 1-chloro-2,2-dimethylpropane.

The acetylide anion, HC≡C⁻, is the conjugate base of the extremely weak acid, acetylene.

So it is both a powerful nucleophile and an extremely strong base — about a billion times as strong as hydroxide ion.

It undergoes $"S"_"N"2"$ reactions with methyl and primary alkyl halides.

But acetylide ion is such a strong base that it undergoes mainly $"E2"$ eliminations with 2° alkyl halides.

And it undergoes only $"E2"$ elimination with 3° alkyl halides.

An $"S"_"N"2"$ reaction goes by backside attack at the α carbon atom.

chemwiki.ucdavis.edu

1-Chloro-2,2-dimethylpropane is completely hindered to backside attack.

The only product is the elimination product.

2-Chloropropane is less hindered.

www.chemgapedia.de

The acetylide ion can attack more readily, so its substitution reaction is faster than on the 3° halide.

Would 2-chloropropane or 1-chloro-2,2-dimethylpropane undergo substitution faster with "HC≡C"^-""HC≡C"^-", "Na"^+"Na"^+?