Q16E - Organic Chemistry (Mcmurry)

Question

Electrostatic potential maps of (a) formaldehyde $\left({\mathbf{CH}}_2\mathbf{O}\right)$ and (b) methanethiol $\left({\mathbf{CH}}_3\mathbf{SH}\right)$ are shown. Is the formaldehyde carbon atom likely to be electrophilic or nucleophilic? What about the methanethiol sulfur atom? Explain.

Step-by-Step Solution

Answer

The carbon atom of formaldehyde act as an electrophile.

The sulfur atom of methanethiol act as nucleophile.

Step 1: Electrophile and nucleophile

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

For example, ${\text{BF}}_{\text{3}}$, ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}{\text{ , AlCl}}_{\text{3}}$

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, ${\text{Cl}}^{\text{-}}$, ${\text{I}}^{\text{-}}$, ${\text{NH}}_{\text{3}}$ , etc.

Step 2: Carbon atom of formaldehyde

The carbon atom of carbonyl carbon is electrophilic because the oxygen atom withdraws electron towards itself which make the carbon atom of the carbonyl carbon more electrophilic. Also, we can say that the carbonyl group gives a nucleophilic addition reaction.

Step 3: Sulfur atom of methanethiol

The sulfur atom of methanethiol contains non-bonding electrons. So the sulfur atom acts as a nucleophile.