The geometry of pyrrolidine and 3 hydroxypyrrolidine CoTPP complexes has been investigated by 'H NMR spectroscopy. The observed couplings and ring current shifts for pyrrolidine-CoTPP are consistent with an envelope conformation with the nitrogen atom out of the ring plane and equatorial coordination of the cobalt atom. A complete analysis of the spectrum was not possible owing to close-coupling of the P-protons.
For 3-hydroxypyrrolidine CoTPP two components in the ratio 85: 15 were observed in the proton spectrum. The spectra of both compounds were completely analysed to give all the couplings in the five-membered rings, and from these the ring conformations were deduced. The major (endo) component exists in an envelope conformation with C-2 out of the plane of the other atoms, and the hydroxy group cis to the NH proton, both in pseudo-axial orientations. The minor (exo) component is also in an envelope conformation, with C-5 out of the plane of the other atoms and the hydroxyl group now trans to the NH proton.
The energy difference of ca 1 kcal mol-' (4 kJ mol-') in favour of the endo component was reproduced by theoretical (MNDO) calculations for protonated hydroxypyrrolidine, but not for the free base. This suggests that the stabilization of the endo component is due to the electrostatic attraction of the hydroxy group and positively charged nitrogen atom.