91Ó°ÊÓ

The structure of morpholine is given below:

Structure of morpholine

The structure of piperidine is given below:

Structure of piperidine

The conjugate acid of morpholine is formed by accepting a proton, i.e. a proton gets added to the nitrogen atom. Its $\mathrm{pKa}$ value is shown below:

Conjugate acid of morpholine

The conjugate acid of piperidine is also formed similarly as that of morpholine. Its formation and $\mathrm{pKa}$value is shown below:

Conjugate acid of piperidine

Thevalue of conjugated acid of morpholine is$\mathbf{9}\mathbf{.}\mathbf{28}$and that of piperidine isrole="math" localid="1652370624470" $\mathbf{11.12}$. From these values, it is clear that protonatedmorpholine is stronger than protonatedpiperidine sinceacidity is inversely proportional to the$\mathbf{pKa}$value.

Moreover, in protonated morpholine, there is an oxygen atom which withdraws electrons inductively while this is not possible in protonated piperidine because there is no oxygen atom.

So, protonated morpholine is a stronger acid than protonated piperidine.