Conjugated Hydrohalogenation (1,2 vs 1,4 addition) Video Lessons

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Problem: 1. Draw the addition products formed when one equivalent of HBr reacts with 2,4-hexadiene. (Draw a single product for each.)1, 2 product addition1, 4 product addition 2. Draw the addition product formed when one equivalent of HCl reacts with the following diene.

FREE Expert Solution

We are asked to determine both the 1,2 and 1,4 products of the reaction below. 


Recall that alkenes are converted to alkyl halides via hydrohalogenation, which occurs in two steps:

(1) protonation – the alkene is protonated, forming a carbocation intermediate and a halide ion. This follows Markovnikov’s rule, which states that the more stable carbocation is formed.


Also, since a carbocation is formed during the reaction, the carbocation may rearrange into a more stable one.


(2) nucleophilic attack – the halide ion comes in and attacks the positively-charged carbon. The stereochemistry for this reaction is unknown since the nucleophile can attack either side of the empty p-orbital.


However, we have 2 consecutive double bonds which make this a conjugated hydrohalogenation. 


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Problem Details

1. Draw the addition products formed when one equivalent of HBr reacts with 2,4-hexadiene. (Draw a single product for each.)

1, 2 product addition

1, 4 product addition 

2. Draw the addition product formed when one equivalent of HCl reacts with the following diene.

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