CONFORMATIONAL CHARACTERISTICS OF KESSANE STUDIED BY 600 MHZ H-1-NMR AND MOLECULAR MECHANICS

The conformational characteristics of kessane were investigated by mea ns of 600 MHz H-1 NMR spectroscopy and molecular mechanics (MM2) calcu lations. Accurate vicinal H-1-H-1 coupling constants were obtained by means of extensive computer simulations. There experimental values wer e compared with coupling constants calculated by the combined use of M M2 calculations and the generalized Karplus equation. It is shown that kessane adopts a single conformation in solution which is only slight ly different from the conformation predicted by the MM2 calculations. The cyclopentane ring of kessane is characterized by a pure 1E conform ation. The cycloheptane ring adopts a conformation which is situated p recisely between the twist-chair TC9BAR and the chair C5BAR conformati on on the pseudo-rotational pathway of the seven-membered ring.