Mass spectra of halogenostyrylbenzoxazoles

► 5-Halogenostyrybenzoxazoles (SBOs) show strong [M−H]+ peaks in their EI mass spectra. ► Strong [M−Y]+ signals occur in the spectra of ortho substituted SBOs. ► The strong [M−H]+ and [M−Y]+ signals can be attributed to a proximity effect. ► Loss of F by the proximity effect preempts loss of Br from the benzoxazole ring. ► Ortho substituted SBOs can be easily distinguished from their meta and para isomers.