Why can't tertiary alcohols be oxidized?

Tertiary alcohols cannot be oxidized because they are already at the highest oxidation state possible for that functional group without breaking carbon-carbon (C-C) bonds. In organic chemistry, oxidation involves the increase in the number of bonds to oxygen or the loss of bonds to hydrogen. A tertiary alcohol features a hydroxyl group (-OH) bonded to a carbon atom that is itself attached to three other carbon atoms.

When trying to oxidize a tertiary alcohol, there is no hydrogen atom on the carbon bearing the hydroxyl group that can be removed to form a carbonyl group (like a ketone) since the carbon is fully substituted with other carbon groups. In essence, any further oxidation would require breaking a C-C bond, which is not typical in the oxidation of alcohols as it would lead to a completely different type of compound and is not considered a typical oxidation reaction.

This characteristic distinguishes tertiary alcohols from primary and secondary alcohols, which can be oxidized to aldehydes and ketones respectively. Therefore, the inability to oxidize tertiary alcohols without incurring structural changes explains why they are seen as already maximally oxidized in this context.