Spectral Studies of Hydrogen Bonding in Alcohols

The phenomenon of hydrogen bonding in alcohols has been known since the early 1900's. Using three series of alcohols, benzyl alcohols, norbornanols and substituted naphthalene alcohols, it was hoped that some meaningful data could be presented to help clarify and expand some of the theories on alcohol association. The techniques to be utilized were ir and nmr spectroscopies.

The synthetic route for those compounds that were not available as alcohols involved reduction of the corresponding acids to alcohols by use of lithium aluminum hydride. The strengths of the various types of hydrogen bonds, intramolecular and intermolecular, were detected by nmr and ir techniques at various concentrations. The 8-substituted-1-hydroxymethyl-naphtalene slope values (8-Br = 25, 8-C1 = 26, 8-0CH₃ = 13, and 8-CH₃ = 32) made it difficult to interpret the intersections on the basis of nmr alone. It appears that in the nmr studies we observe this difficulty, due to steric, electronic and polarizability effects, of forming the hydrogen bond, and only in the ir data do we get an idea of the actual strength of the hydrogen bond formed. It was observed for 3-endo-phenyl-2-endo-norbornanol that the slope value (8.3) and ir frequency shift (10 cm^-1) correlate well with the steric interactions involved in the cis-di-endo compound.

The slope values and frequency shifts give us an idea of the strength of the intramolecular association and the energy relationship between the monomer and dimer. The hydrogen bonding appears to lower the energy of the monomer relative to that of the dimer by virtue of the internal bonds.