Q 29P - Organic Chemistry (Mcmurry)

Question

What product(s) would you expect from the reaction of 1,4-hexadiene with NBS? What is the structure of the most stable radical intermediate?

Step-by-Step Solution

Answer

                           Formation of major and minor products

Most stable radical intermediate

Step-by-Step Solution Step 1: N-bromosuccinimide

NBS (N-bromosuccinimide) is a brominating reagent that is used to introduce a bromine atom at the allylic and benzylic positions. This reaction occurs via a free radical mechanism in order to carry out radical substitution and electrophilic addition reactions.

Step 2: Reaction of NBS with 1,4-hexadiene

The reaction of NBS with 1,4-hexadiene is as follows:

                           Formation of major and minor products

There are two products possible for this reaction, 3-bromocyclohexa-1,4-diene and 5-bromocyclohexa-1,3-diene due to the formation of two intermediates during the mechanism of the reaction.

Therefore, the two possible expected products of this reaction are as follows:

3-bromocyclohexa-1,4diene                           5-bromocyclohexa-1,3-diene

The most stable intermediate will result in the formation of the major product. Thus, during the reaction,1,4-hexadiene undergoes a radical formation, which is followed by a chemical conversion that leads to the formation of the most stable radical given as:

                                  Formation of most stable radical

Thus, the most stable intermediate is as follows:

Most stable radical intermediate