A Neighboring Group Effect of Carbonyl as Shown in the Mass Fragmentation Patterns of 4-Oxochroman-5-acetic Acids and of Some Related Compounds

Abstract

Two examples of a neighbouring group effect of carbonyl first observed with 4-oxochroman-5-acetic acids are shown to occur quite generally during electron impact mass spectrometry of 2-acylbenzeneacetic acids, 2-acylbenzoic acids and their methyl esters. The free acids readily give the [parent - CO₂] ion. 2-Acylbenzeneacetic acids and their methyl esters after loss of water or methanol, respectively, as a first step, lead to very stable isobenzofuran radical cations which form the base peaks in the mass spectra of the esters.