Question

Question #1560d

Answer 1

Nucleophilic substitution by `"KCN"` gives an alkyl cyanide, while `"AgCN"` gives an alkyl isocyanide because `"KCN"` is ionic and `"AgCN"` is covalent.

Explanation:

Alkyl halides react with alcoholic `"KCN"` to form alkyl cyanides

`"KCN"` is an ionic compound. The nucleophile is the cyanide ion

`[:stackrel("-1") ("C")"≡N:"]^"-"`

The carbon atom is the nucleophile and the reaction is

`underbrace("RX")_color(red)("alkyl halide") + :stackrel("-")("C")"≡N:" stackrel("Δ"color(white)(m)) (→)underbrace("RCN")_color(red)("alkyl cyanide") + "X"^"-"`

Alkyl halides react with alcoholic silver cyanide to form alkyl isocyanides.

The electronegativity difference between `"Ag"` and `"C"` is so small that the `"Ag-C"` bond is over 90 % covalent.

The nucleophile is `"Ag-C≡N:"`.

The carbon atom is no longer available to act as a nucleophile, but the N atom can still attack the alkyl halide.

`underbrace("RX")_color(red)("alkyl halide") + "AgCN:" stackrel("Δ"color(white)(m)) (→)underbrace("RNC")_color(red)("alkyl isocyanide") + "AgX"`