Complete the following reactions: a. `H-underset((A))C-=C-Hoverset(1mol)underset(NaNH_(2))rarr(B)overset(CH_(3)Br)rarr(C)`

g. `H-underset((A))(C-=C)-Hoverset(1mol)underset(NaNH_(2))rarr(B)overset(Br(CH_(2))_(8)Br)rarr(C)`

Explanation

a. `HC-=C-Hoverset(1mol)underset(NaNH_(2))rarrHC-=overset(ddotTheta)underset((B))C-overset(o+)Naoverset(CH_(3)Br)rarrunderset((C))underset(Prop-1-"yne")(overset(1)(HC)-=overset(2)(C)-overset(3)(CH_(3))+NaBr)`
b.
With `RI` and `RB_r, SN^2` reaction is dominant because `I^(ɵ)` and `Br^(ɵ)` are better leaving groups. But `I^(ɵ)` is a better leaving group than `Br^(ɵ)`. So with RI the reaction is faster than with `RBr`.
c. With `RCI`, `E2` reaction is dominant over `SN^2` reaction.
`CI^(ɵ)` is a poor leaving group than either `Br^(ɵ)` or `I^(ɵ)`.
Moreover, `CI^(ɵ)` is a better acid-strengthening group than `Br^(ɵ)` or `I^(ɵ)`, which facilitates the removal of `beta`-proton from the alkyl halid. Furthermore, alkynides are powerful bases but mild nucleophiles.

d.
e. `underset((B))(HC-=C^(ddotTheta))overset(D_(2)O)rarrunderset((G))underset(1-"Deuterio-ethyne")underset(1-d-"ethyne or")(HC-=CD)`
f. `HC-=CHoverset(2mol)underset(of NaNH_(2))rarrunderset(Ethynide dianion)underset((B_(1)))(overset(ddotTheta)C-=overset(ddotTheta)(C) )overset(D_(2)O)rarrunderset(1,2-"Dideuterio-ethyne")underset(or)underset(1,2-Di-d-"ethyne")underset((H))(D-C-=C-D)`
g.
First reaction, i.e., alkylation of acetylide, occurs with difficulty. The second alkylation giving rings is again difficult. Intramolecular cyclisation leading to rigs with more than six C atoms is difficult and the intermolecular reaction predominates.
If a very dilute solution of `NaNH_2` is used, then intramolecular cyclisation takes place, thereby making it difficult for two molecules to collide to give the intermolecular alkylation.
Intermolecular alkylation: