Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

12. Alcohols, Ethers, Epoxides and Thiols

Leaving Group Conversions - Using HX

Next Topic

Alcohols are terrible leaving groups. So we’re going to learn an entire class of reagents whose sole job is to convert alcohol into better leaving groups. 

1

concept

Why do we need to convert Alcohol into a good leaving group?

clock
2m
Play a video:
Was this helpful ?
0

We’re aiming to turn alcohols into alkyl halides or sulfonate esters. Let’s explore the different ways to accomplish this. 

The simplest way to theoretically convert alcohols into alkyl halides is just to react them with a strong halohydric acid (HX). There are some complications associated with this conversion however.

 

Can you predict what they are? (Three major complications given below).  

2

concept

Using HX acids via SN1 reaction.

clock
7m
Play a video:
Was this helpful ?
0

This is the predominant mechanism for strong halohydric acids with 2° and 3° alcohols. 

Content
3

concept

Using HX acids via SN2 reaction.

clock
2m
Play a video:
Was this helpful ?
0

This is the predominant mechanism for strong halohydric acids with 1° alcohols.

Content

Complications: Strong HX acids conversions come with three major complications.

  1. Regiochemistry of products:Carbocation intermediates can rearrange.
  2. Stereochemistry of products:Racemic products are non-stereo specific.
  3. Competition of Elimination mechanisms:Some product won’t even be an alkyl halide.   

These complications render this method mostly useless. Sorry not sorry.