I have a few homework problems I am stuck on. I am already struggling with the material and trying to teach myself as much as possible, so any help with these 2 questions would greatly appreciated!

 

How would you make the following compounds starting with acetylene. If compound cannot be prepared using this method say so.

1. 4-methyl-2-hexyne

2. 5-methyl-2-hexyne

 

I am using the David Klein Organic Chemistry textbook and I am finding that there are not too many examples like this to guide me and the teacher did do any problems in class, just assigned them.

Edited November 18, 201213 yr by camurphy519

You can use the fact that the alpha hydrogen of actylene is acidic. So, add a base such as NaOH to it to abstract the hydrogen and form a carbanion.

 

For the first product, add 2-methlychlorobutane. The actylene carbanion will act like a nucleophile and substitute the chlorine in 2-methlychlorobutane. You now have 3-methylpentyne. Now, the hydrogen on the other side of the triple bond is also acidic, so, you can form a carbanion from that too. Now react that with a chloromethane and you will obtain your product.

 

Repeat to form second product The only change is to use 3-methlychlorobutane instead of 2-methlychlorobutane.