# Why does treatment of a geminal dihalide with sodium amide lead to an alkyne and not an allene?

I've come across the following problem in Klein's Organic Chemistry, 2nd edition:

However, I'm a little bit confused about why the terminal alkyne is produced. I believe that an allene should be formed via stepwise elimination of HBr, using the strong base NaNH2. The first elimination should give the more substituted, more thermodynamically stable alkene (Zaitsev's rule):

Why does the former occur instead of the latter?

• monosubstituted acetilenes are deprotonated by sodium amide, allenes are not. Since alkenes and allenes can converse to each other in amides via deprotonation, typically even if you put a nonterminal allene or alkyne into sodium amide solution, it transforms into terminal alkyne. – permeakra Dec 8 '15 at 22:10
• I think the first proton is abstracted from the primary carbon due to the following reasons: Primary is less sterically hindered and hence is easily accessible by $\ce{NH2-}$ ion. Also, even a partial negative charge on carbon in the transition state of the reaction is better off on primary carbon. – ShankRam Feb 2 '16 at 4:04