THE CONFORMATIONAL COMPOSITION OF 3-BUTEN-1-OL, THE IMPORTANCE OF INTRAMOLECULAR HYDROGEN-BONDING

The conformations of 3-buten-1-ol (7), and its model compounds cis-6-m ethyl-3-cyclohexen-l-ol (6), 3-cyclopenten-l-ol (7) and epicholesterol (9) have been investigated by FT-LR and H-1 NMR spectroscopy. The ene rgies and geometries of 1, 6 and 7 were also investigated by molecular mechanics, semiempirical molecular orbital and ab initio calculations ; while 9 was investigated by molecular mechanics only. The objective of the work was to study the conformational composition and importance of intramolecular OH...pi hydrogen bonding for this composition in 1. Only two conformers of 1 have a geometrical possibility for intramole cular hydrogen bonding: Conformers 12 and 13 (Fig. 1). Compounds 6 and 7 were used as models for Conformer 12, while 9 was used as a model f or Conformer 13. The investigations showed that Conformer 13 is the on ly hydrogen-bonded conformer, and that Conformer 12 is not intramolecu larly hydrogen bonded. Conformer 13 was the most populated conformer, while Conformer 12 was hardly populated. The combination of experiment al and theoretical data, and the use of model compounds was found nece ssary to obtain this conclusion. (C) 1998 Elsevier Science B.V. All ri ghts reserved.