Which Is Benzylic Hydrogen?

Hint: In organic chemistry, Benzylic hydrogens refer to the hydrogen atoms that are attached to the carbon atom just next to or in other words the carbon atom adjacent to the benzene group. For example: In ethyl benzene carbon next to benzene has two hydrogen atoms only.

Is benzylic hydrogen acidic?

Agree, 1 is more acidic due to benzylic position carbocation as well as you can form many resonance structures. Alkynes have a smaller pKa than benzylic Hydrogens, so 2 is more acidic.

Why are benzylic hydrogens more reactive?

The benzylic position is quite reactive and presents a useful synthetic tool for preparing many aromatic compounds. The reason for this reactivity is the resonance stabilization of the benzylic carbon regardless if the reaction goes through an ionic or radical mechanism.