Which of the following species are likely to be nucleophiles and which electrophiles? Which might be both?

Electrophiles are the positively charged species that attack the electron-rich center.

For example,${\mathbf{BF}}_3\mathbf{,}\mathbf{}{\mathbf{H}}_3{\mathbf{O}}^{+}\mathbf{,}{\mathbf{AlCl}}_3\mathbf{.}$

Nucleophiles are the electron-rich centers or negatively charged species that attack electron-deficient centers.

Neutral molecules containing lone pair of an electron can also act as a nucleophile. For example,${\mathbf{Cl}}^{-}\mathbf{,}{\mathbf{I}}^{-}\mathbf{,}{\mathbf{NH}}_3\mathbf{,}$ etc.

(a)${\text{CH}}_{\text{3}}\text{Cl}$

The carbon of chloromethane is delta positive as chlorine withdraw electron towards itself making carbon partially positive. Therefore it acts as an electrophile.

(b)${\text{CH}}_{\text{3}}{\text{S}}^{\text{-}}$

As it is negatively charged hence it acts as a nucleophile.

(c)

Compound C

As the nitrogen atom contains lone pair of electrons so it acts as a nucleophile.

(d)

Compound C

The Carbonyl group of acetaldehyde gives a nucleophilic addition reaction it indicating that the carbonyl carbon carries a partial positive charge. Hence it acts as an electrophile.