(±)Alkyl 3-hydroxy-1-azabicyclo[2.2.2]octane-3-carboxylates: conformational preferences of the alkoxycarbonyl group

Molecular mechanics, ab initio (RHF) and density functional (DFT/B3LYP) methods are applied to investigate the conformational preferences of the methoxycarbonyl group of the (±)methyl 3-hydroxy-1-azabicyclo[2.2.2]octane-3-carboxylate. ¹H and ¹³C chemical shifts are also calculated by the GIAO/DFT approach and compared with experimental values. Both theoretical and experimental data account for almost eclipsed conformations with different degrees of distortion from the ideal geometry. It is found that calculations at the B3LYP/6-311G(d,p) level are relatively more reliable to explain the behaviour of the alkoxycarbonyl moiety of 2-hydroxyesters derived from the (±)3-hydroxy-1-azabicyclo[2.2.2]octane-3-carboxylic acid.