2-ETHYNYLADAMANTAN-2-OL - A MODEL-COMPOUND WITH DISTINCT OH...PI AND CH...O HYDROGEN-BONDS

Vibrational spectroscopy has been used to demonstrate that the extremely short OH ... pi and =C-H ... O intermolecular contacts in crystalline 2-ethynyladamantan-2-ol are due to strong interactions, which may unambiguously be typified as hydrogen bonding in view of the behaviour of OH and =C-H stretching and bending modes. The XH stretching vibration shifts to lower frequency, becomes broader and more intense and has a positive frequency-temperature coefficient, whereas the XH bending modes shift to higher values and show a negative frequency-temperature coefficient. Solution spectra of the title compound in apolar solvents served as a reference for the ''free'' molecule. Variable-temperature measurements together with deuteration experiments have been performed to establish the correct assignment of these characteristic modes.