Which is the correct arrow pushing formalism for the following acid/base reaction?

• A.
• B.
• C.
• D.

Answer: (B)

Verified step by step guidance

1. Identify the reactants: The first reactant is the amide ion (H₂N⁻) with a negative charge on nitrogen, which has two lone pairs of electrons. The second reactant is a terminal alkyne (H-C≡C-R) where R is a carbon chain.
2. Recognize the role of each reactant: The amide ion acts as a base, and the terminal alkyne acts as an acid in this reaction.
3. Determine the direction of electron flow: The lone pair of electrons on the nitrogen of the amide ion will attack the hydrogen atom of the terminal alkyne.
4. Draw the first curved arrow: This arrow should start from the lone pair on the nitrogen and point towards the hydrogen atom of the alkyne, indicating the formation of a new N-H bond.
5. Draw the second curved arrow: This arrow should start from the H-C bond of the alkyne and point towards the carbon atom, indicating the breaking of the H-C bond and the formation of a carbanion (C⁻).