Comparison of the Mass Spectrometry Behaviour of Fluorinated Ethers and Sulphides

The mass spectrometric behaviour of two pairs of fluorinated vinyl- and allyl-ethers and thioethers has been studied in detail with the aid of metastable ion data and accurate mass measurements. Clear differences have been observed between the two sets of compounds; while for the ethers the McLafferty rearrangement with ethylene loss represents a highly favoured decomposition route, for the thioethers the loss of the ethyl radical is preferred. Some decomposition routes, common to all the compounds examined, suggest the presence of hydrogen atom bridging between carbon and fluorine atoms. Theoretical calculations have shown that such a quasi C—H—F structure is already present in the neutral molecule in its ground state