The nominal butyl ester ion in the mass spectra of long-chain n-alkyl esters: A postscript

n‐Octadecyl benzoate, taken as a model for long‐chain n‐alkyl carboxylates generally, loses C14H28 under electron impact to yield a product with the same elemental composition as the butyl benzoate molecular ion. This product retains quantitatively one hydrogen from C‐6, and seems to be formed as an oxygen‐protonated 4‐benzoyloxybutyl radical. It reacts further to lose H2O, in which deuterium labeling demostrates that the second hydrogen atom comes predominantly from C‐4. The intermediate reorganization, for which the driving force is presumably furnished by the instability associated with a primary radical, is pictured in terms of cyclization via bonding between the C‐4 radical site and the benzoyl carbon concerted with hydrogen migration via a 4‐membered quasicyclic transition state.