Question

why will be the reaction unsuccessful if NaNH2 and Et-Br are added together?
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Answer 1

Explanation:

this once was my doubt...terminal alkynes are preferred because the acidic hydrogen at the terminal carbon is acidic(sp hybrid of Carbon) and which when taken up by the base gives a species with a negative charge on sp hybridized carbon which is indeed stable...so this provides the incentive for forming a terminal alkyne as the final product.

Trusted source: Jerry March Organic Chemistry 6th edition.

When the base is NaNH2 1-alkynes predominate (where possible), because this base is strong enough to form the salt of the alkyne, shifting any equilibrium between 1- and 2-alkynes. When the base is OH−OHX− or OR−ORX−, the equilibrium tends to be shifted to the internal alkyne, which is thermodynamically more stable.