THE MASS SPECTRA OF THREE DEUTERATED BROMOBUTANES

Abstract

The mass spectra of 1,1-dideutero-1-bromobutane, 1,1,1,3,3-pentadeutero-2-bromobutane, and 1,1,1,2,3,3-hexadeutero-2-bromobutane have been obtained using 70-volt ionizing electrons. The cracking patterns of the deuterated molecules are compared with those of the undeuterated bromobutanes. It is shown that no hydrogen–deuterium exchange occurs in certain ions formed from the parent ion by simple bond break but that extensive exchange of hydrogen and deuterium occurs in ions formed by further decomposition of unsaturated daughter ions.Formation of HBr⁺ or loss of HBr to form C₄H₈⁺ from 2-bromobutane is shown to favor sterically the hydrogen on carbon 4 and not to involve that on carbon 2. However, in the case of 1-bromobutane, formation of these ions does not appear to involve any particular hydrogen preferentially, because if one assumes that all hydrogens in the molecule are involved, then the hydrogen on carbon 1 appears to be involved to an almost statistical extent.In two cases the isotopic substitution so modifies the rate of a metastable reaction that the metastable peak disappears from the spectra of the deuterated species.