Dynamic Fluorine-19 Polarization in Fluorinated Strained Cyclic Alkanes and Alkenes.

摘要

Studies of dynamic polarization of F19 nuclei in a series of perfluorocycloalkanes and perfluorocycloalkenes and their partially chlorinated analogues are reported. The experiments test effects that changes in the internal structure of the molecule have on the behavior of the peripheral fluorine atoms in nonaromatic species. With galvinoxyl interactions are dominated by dipolar coupling of the spins, with ultimate enhancements in the range -237 to-270. For the perfluorocycloalkanes enhancements are predominantly dipolar (-171 to -213 to -270. For the perfluorocycloalkanes enhancements are predominantly dipolar (-171 to -213 for bis(diphenylene)phenylallyl (BDPA), -182 to -227 for 2,2-diphenyl-1-picrylhydrazyl (DPPH)), with little variation for the four-, five-, and six-member ring species studied. The fluorines on the saturated carbons of the 1,2-dichloroperfluorocycloalkenes show more scalar coupling than the perfluorocycloalkanes (-143 to -158 for BDPA, -164 to -179 for DPPH), but the highest degree of scalar coupling is obtained for the perfluorocycloalkenes. The enhancements of the fluorines attached to unsaturated carbons are separated from the total observed enhancement and are shown to produce couplings significantly more scalar than others previously observed (+2 to -52 for BDPA, +256 to +223 for DPPH.) No evidence of correlation of DNP results for polarization of peripheral fluorine atoms on molecules when compared with high field NMR results is found. (Author)