Question

What causes ketones?

Answer 1

Ketones are the result of oxidation of secundary alcohols.

Explanation:

A secundary alcohol is an alcohol where two other C-atoms are attached to the one having the alcohol (OH) group, like in 2-propanol `CH_3-CHOH-CH_3`

When oxidized, the H from the carbon-atom and the H from the OH group combine with O to form water, and the O on the carbon is now double-bonded:
propanon `CH_3-CO-CH_3`

This compound cannot be easily oxidized any further.