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What is involved in the mechanism of the reaction between aqueous sodium hydroxide and 1-bromobutane?

A. attack by a nucleophile on a carbon atom with a partial positive charge

B. heterolytic bond fission and attack by a nucleophile on a carbocation

C. homolytic bond fission and attack by an electrophile on a carbanion

D. homolytic bond fission and attack by a nucleophile on a carbocation

I think that A and B would be correct answers, but the correct answer is only A. Bromine accepts both two electrons from the carbon atom and the nucleophile attacks on that carbocation of the carbon atom. Why choice (B) is incorrect? I also searched the internet and found that this reaction is SN1, but why it occurs with the primary carbon, which is usually a reactant in SN2 reaction.

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    $\begingroup$ Have you got a link to the internet site claiming this to be SN1 ? I really dislike these questions, they give the impression to the student that chemistry is applying some textbook rules when generally in reality you either form some hypothesis and execute a suitable experiment (or experiments) to disprove/prove it or you search the literature for someone that has already done this. Maybe it is better to ask the questions as "What is the most likely mechanism/product to form etc ..." $\endgroup$ – K_P Feb 28 '16 at 13:41
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    $\begingroup$ Sorry for the rant above, I forgot to mention that the textbook answer is that it should be SN2 as a primary halide. $\endgroup$ – K_P Feb 28 '16 at 13:51
  • $\begingroup$ So sorry, I misread it. Actually, it is as what you said that it should be SN2. At first, I misconception about the strongly charged nucleophile. @K_P $\endgroup$ – anonymous Feb 29 '16 at 11:26
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Well your thinking is absolutely right but only for tertiary halogenoalkane as this is a prinary halogenoalkane it will follow SN2 mechamism. In which necleophile attacks on a partial positive carbon

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