# NH2- and Primary Alkyl Halides: Sn2 vs E2

When we mix 1-bromopropane and $\ce{NaNH2}$, what happens? Which reactions wins out to make the major product?

My textbook says that primary alkyl halides give mainly SN2 products unless the base is hindered ($\ce{t-BuO-}$) (where E2 would win out).

But it contradicts itself when you have for example 1,2-dichlorobutane and you add three molar equivalents of $\ce{NaNH2}$ and then $\ce{NH4Cl}$ to have an alkyne. Why is there no SN2 going on in that case?