Mass Spectrometric Analysis of the Isotopomeric Species in the Solvolysis of 1,2-Diphenyl-2-phenylvinyl Bromide in 70percent HOAc-30percent H2O

Article abstract of DOI:10.1021/jo00155a019

The distributions of products from four possible isotopomeric triphenylvinyl cations derived from solvolyses in 70percent HOAc-30percent H2O of the doubly labeled 1,2-diphenyl-2-<2H5>phenyl<2-13C>vinyl bromide (1-Br-2-13C-2-Ph-d5) were determined by mass spectrometry.The electron-impact spectra of the reaction products, the various labeled 1,2,2-triphenylethanones derived from the four isotopomeric cations, did not give consistent or reproducible results probably because of complications by multiple fragmentation.After degradation of the reaction products to give (C6H5)2CO, (C6H5)2(13)CO, C6H5(C6D5)CO, and C6H5(C6D5)13CO, the chemical ionization spectra of these isotopomeric benzophenones gave, for each solvolysis reaction, the relative amounts of the four isotopomers and hence the distribution of products derived from the four isotopomeric triphenylvinyl cations.The results obtained showed agreements between the mass spectrometric data and previous 14C scrambling data or the 13C scrambling data obtained in the present work by 13C NMR, with the 14C or 13C scrambling data showing greater precision.For example, the scrambling of the 13C label from C-2 to C-1 as determined by 13C NMR for the solvolysis of 1-Br-2-13C-2-Ph-d5 in 70percent HOAc in the presence of various amounts of added NaOAc was found to be 15.2+/-0.5percent, while the analogous value derived from the CI spectral analysis was 13.9+/-2.2percent.The observed formation of the various possible isotopomeric products also demonstrated definitely the occurence of successive 1,2-phenyl shifts in the triphenylvinyl cation, and this would not have been detected with the use of only a singly labeled substrate.