HIGH-PRESSURE 2D NOESY STUDY OF LIQUID 2-ETHYLHEXYL BENZOATE

A two-dimensional nuclear Overhauser effect spectroscopy (NOESY) study of the complex fluid 2-ethylhexyl benzoate (EHB) was performed at -20-degrees-C and 0-degrees-C up to pressures of 3000 bar. The high-pressure/low-temperature capability of the NMR set-up allowed the experiments to be done under conditions of very slow molecular motion where proton homonuclear cross relaxation rates were large in magnitude and NOESY cross peaks were significantly intense and fast-growing. Intramolecular cross relaxation rates were determined by measuring cross peak build-up rates as a function of isotopic dilution of EHB in perdeuterated EHB (EHB-d22) and extrapolating to infinite dilution. A direct correlation between the rate of cross relaxation and viscosity/temperature was found and was explained in terms of the Debye expression. Insight into the time scales involved in molecular reorientation was also gained by calculation of correlation times. Internuclear cross relaxation rates were similarly investigated and related to the inverse of the rate of translational diffusion through Torrey's translational model for relaxation. Finally, internuclear distances calculated from intramolecular cross relaxation rates were used in conjunction with a molecular mechanics program to gain qualitative information about possible EHB conformations.