Question

why is there no such thing as methanone or ethanone? i.e. H-C=O-H and CH3-C=O-H respectively ?(Taking -C=O- as the formula for ketones. )

Answer 1

Because functional group ketone occurs only on inner carbons and not on terminal ones. To obtain a ketone we need minimum 3 carbons so the one in between has the ketone group -C=O- that's why methanone and ethanone do not occur.