First field free metastables as a structural probe for differentiating isomers of aliphatic alcohols

In the electron impact mass spectra of esters of aliphatic alcohols, a series of first field free region metastables are observed for the formation of the acylium ion, [R.CO]+, from a set of precursor ions created by fragmentation at each successive CC bond in the aliphatic alcohol chain. The positions and intensities of these metastables are characteristic of sites of chain branching and of double bonds in the alcohol moiety.