A study of15N formamide oriented in a lyotropic nematic phase

Publisher Website
Google Scholar
Abstract
15N formamide is soluble in a single multi-component nematic lyotropic phase and gives proton magnetic resonance spectra typical of partially oriented solutes in nematic solvents. A technique is developed to prevent amide proton exchange in the medium by controlling the pH of the added water. The spectrum was analysed as an ABCX nuclear spin system with the inclusion of scalar spin couplings determined in previous studies of the molecule in isotropic media. The six independent dipolar coupling constants, though very precise, do not suffice to solve the structure of the molecule. The structure determined by Costain and Dowling from microwave spectra is used as a starting point to test the consistency of experimental dipolar couplings and motional constants. A structure which deviates in small respects from that deduced from the microwave spectra is able to reproduce all six dipolar coupling constants very accurately and to give a consistent set of five motional constants. The use of three motional constants in any combination with the six dipolar couplings does not give consistency with experiment. We conclude that the four ABCX nuclei are not co-planar and that the molecule persists in the non-planar form in this solution for periods greater than 10-1 sec.