The carbonyl carbon in carboxylic acids does not withdraw electrons from the hydroxyl oxygen. Instead, the electronegative oxygen atom of the carbonyl group is partially negatively charged due to its higher electronegativity compared to carbon. This partial negative charge attracts the electron density towards itself, creating a partial positive charge on the carbonyl carbon. This polarization of the carbonyl group makes the carbon-oxygen bond polar, with the oxygen atom being partially negative and the carbon atom being partially positive.
In carboxylic acids, the presence of the electron-withdrawing carbonyl group enhances the polarity of the O-H bond in the hydroxyl group. The partial positive charge on the carbonyl carbon further increases the partial positive charge on the hydrogen atom of the hydroxyl group. This increased polarization of the O-H bond results in a higher dipole moment and greater polarity of the bond.
It's important to note that while the carbonyl carbon withdraws electron density in some cases, in carboxylic acids, the polarization of the O-H bond is primarily due to the electronegativity difference between the oxygen and hydrogen atoms, rather than the carbonyl group's influence.