AbstractIt is well known that intermolecular hydrogen-bonding is concentration dependent. It is also known that the H chemical shift of an hydroxyl proton is dependent upon concentration. H NMR spectroscopy has therefore been used to study hydrogen-bonding in solution.
It was found previously by Becker, Liddel and Shoolery that at very high dilution in CC1 4 , the chemical shift of the hydroxyl group in ethanol is directly proportional to concentration. This was also found by Ouellette et al, for cyclopentanol and cyclohexanol in 0014. The present author has extended this work to these two compounds and other alicyclic alcohol systems in both CCl^ and d-chloroform, and that a chemical shift at infinite dilution can be used as a test of the presence of intramolecular hydrogen-bonding.
Infra red and NMR methods are compared in the study of hydrogenbonding in a series of alicyclic diols and from the results obtained, predictions are made on their preferred conformations.
The conformational preference of the hydroxyl group in cyclohexanol is determined by the concentration vs. chemical shift method and compared with other standard NMR methods, namely: peak area measurement at low temperature; chemical shift of the a-proton and a lanthanide shift method (in which it is suggested that the complexation does not affect the equilibrium). The chemical shift vs. concentration method quoted above is then used to establish the conformational preferences of the phenyl and ethyl groups in phenyl- and ethylcyclohexane.
The lanthanide shift method is also presented for 1-ethylcyclohexanol and these results cast some doubt on the validity of the original postulation of the equilibrium not being affected.
These experiments rely on a determination of the equilibrium constant between axial and equatorial conformers and a treatment of the accuracy of the method is presented.
Chemical shift at infinite dilution is also used to study intermolecular hydrogen-bonding and as the basis for analysis of mixtures of alcohols.
This technique can therefore be used in the quantitative and qualitative study of hydrogen-bonding and conformation in alicyclic systems.
|Date of Award||1978|
|Supervisor||Ieuan Morris (Supervisor)|