Fragmentation of a phenyl methyl ether under electron impact normally occurs by fission of either C-O bond to give ions due to loss from the parent of a methyl radical or, with rearrangement of one hydrogen, a formaldehyde molecule. In the latter case a hydrogen atom may be subsequently lost if a stable tropylium ion may thereby result. If there are present ortho- or para-substituents which are capable of forming a quinonoid structure involving the ether oxygen after removal of a methyl radical, then loss of formaldehyde does not occur.