PUB - Publikationen an der Universität Bielefeld

The fast ring-to-ring proton transfer in protonated 1,4-bis(-phenylalkyl)cyclohexanes [(5a)+ H]+, [(5b+ H)]+, and [(6)+ H]+ has been studied by chemical ionization mass spectrometry. The cyclohexane-1,4-diyl unit exerts a distinct stereocontrol upon the rate of proton exchange. Complete proton equilibration is found for protonated cis-dibenzylcyclohexane [(5a)+ H]+, whereas in the trans isomer [(5b)+ H]+ the interannular proton transfer is strongly decelerated. The trans-bis(- phenylethyl) homologue [(6)+ H]+ is found to represent an intermediate case. By comparison with simpler protonated diphenylalkanes the rate of the interannular proton transfer for metastable ions [(5b)+ H]+ and [(6)+ H]+ is estimated to lie within the limits 5 × 105 and 106s–1.