Intramolecular OH/pi interaction: the molecular structure and conformations of 3-hexyn-1,6-diol

The molecular structure and conformational composition of 3-hexyn-1,6-diol have been studied by the gas electron diffraction method and by ab initio c alculations. Four conformers (AA, G+G-, GSG+ and GA) have been taken into a ccount. The experimental data are In accordance with a conformational mixtu re consisting of 62.2% GG (equal parts of G+G- and G+G+) and 37.8% GA with a standard deviation of 10.3%. Similar results were, however, obtained when a small contribution (0 less than or equal to x less than or equal to 12%) from the high energy AA conformer was introduced and the other forms were properly corrected (GG (62.2+x%); GA (37.8 - 2x%)). From the experimental d ata the total amount of gauche contribution in the two parts of the molecul e is accordingly estimated to be in the region 76.0-86.3%. The GG and GA co nformers are characterized by the formation of two, respectively one, OH a hydrogen bonds. (C) 2000 Elsevier Science B.V. All rights reserved.