# What are the 7 ketones with formula C6H12O?

We know that a carbonyl group can only exist at spots that give an $s {p}^{2}$ hybridization, so there is no structure for the carbonyl on carbon 3 when carbon 3 has a tert-butyl group. Similarly, there is no structure for which the carbonyl is on carbon 3 while the sec-butyl is also on carbon 3.