The cyclopentanone ring puckering

The complete analysis of the H-1 NMR spectrum of cyclopentanone (CPO) and the full ralaxed optimization of its structure at the 4-3IG level have been carried out. The endocyclic torsions angles φ (0) and φ (1) estimated by the R-value method from the vicinal HH couplings are 9 and 12° larger than the respective theoretical 4-3IG values which closely correspond to the empirical electron diffraction (ED) ones. When the theoretical tilts of the CH₂ groups are taken into account the values estimated by the R-value method decrease by ≈4.5°.