During my PhD, about fifty years ago, I had reason to use 4-t-butyl aci-nitro cyclohexane and found it to be remarkably stable. Usually aci- nitro compounds revert to nitro compounds very quickly unless they are stabilised by conjugation. There is no conjugation in this compound and the t-butyl group only serves to keep the cyclohexane ring in the chair configuration. There is no excessive steric hindrance in the chair configuration. So what's going on? My guess is that the conversion of the aci-nitro form to the thermodynamically more stable nitro form happens by the transfer of the OH proton to the carbon via the carbanion and that carbanion can be in the boat or the chair configuration. However, only in the boat configuration does the molecular orbital come near enough to the OH proton for the transfer to occur. Is this on the right track? I am not very familiar with molecular orbital theory (it had hardly started 50 years ago) so I would appreciate some input that I might be able to understand.