Question

Which hydrogen in pseudoephedrine, the nasal decongestant in the commercial medication Sudafed, is most acidic?

Short answer

In pseudoephedrine, the hydrogen atom bonded to oxygen is the most acidic.

Step-by-step solution

Acidic hydrogen

The hydrogen (H) atom that is easily dissociated from a compound/molecule is termed acidic hydrogen.

Acidic Strength

The acidity of a hydrogen atom depends on the ‘electronegativity’ of the atom to which it is bonded.

The higher is the atom's electronegativity, the more acidic is the hydrogen attached to it. The electronegative atom pulls the electron density towards itself, leading to the generation of ${\mathrm{H}}^{+}$ions.

Acidity of hydrogen atoms in pseudoephedrine

The structure of pseudoephedrine is shown below.

The most acidic hydrogen in pseudoephedrine

Pseudoephedrine consists of hydrogen atoms bonded to carbon, oxygen, and nitrogen.

Of these, oxygen is the most electronegative. Hence, the hydrogen atom bonded to it is the most acidic.