[DannyBoi]

Hi,

I am a bit confused about synthesis of alkyl halides from alcohols. In my notes, I wrote that with 2^o and 3^o alcohols, if you use PBr₃ to form a bromine where the OH was, you should watch out for rearrangement in the product. But in my notes there was no such warning for using HCl to form the alkyl halide from a 2^o or 3^o alcohol. But in this video, this guy says the opposite towards the end of the video, namely that rearrangement can occur with HCl, but does not occur with PBr₃ or SOCl₂. Any clarification is appreciated.

http://www.youtube.com/watch?v=tJx8yRyCa9M

[james_a]

Any reaction which proceeds through a carbocation intermediate has the potential for a rearrangement reaction.

Your notes should definitely have a warning for rearrangement reactions with HCl with 2° or 3° alcohols as they tend to proceed through carbocations.

As described in the video, PBr3 and SOCl2 tend to proceed through SN2 reactions... esp for primary and secondary. It is generally taught that these reactions occur with inversion of configuration. Generally speaking in Org1/Org2 it is rare to see it taught that the reaction proceeds through a carbocation. What textbook is your course based on?

If you are brave enough to look for PBr3 in March's Advanced Organic Chemistry you will get more of the true picture about PBr3 for tertiary alcohols.