Conformational analysis—IV: A lanthanide induced shift (LIS) NMR investigation of the conformation and relative conformer energies of trans and cis 2-decalone

Abstract

The solution conformation of trans-2-decalone and the conformational population of cis-2-decalone has been determined by LIS analysis. The angle of pucker (α) of the ketone ring in trans-2-decalone is 51 ± 2°, identical to that of cyclohexanone, but different from that determined for substituted decalones in the solid state, in which significant flattening of the ring occurs. The steroidal conformer of cis-2-decalone, when the latter is complexed to Yb(fod) 3 in CDCl 3, found to be preferred over the non-steroidal conformer by a ratio of 55:45, in contrast to the preference reported from the low temperature 13C NMR spectrum for the non complexed ketone in CH 2Cl 2. The two determinations can be combined to give the enthalpy difference in favor of the non-steroidal conformer of ca 0.8 kcal mole −1.