ANIONIC MIGRATION IN AROMATIC SYSTEMS EFFECTED BY COLLISIONAL ACTIVATION - UNUSUAL FRAGMENTATIONS OF DEPROTONATED ANILIDES CONTAINING METHOXYL AND ETHOXYL SUBSTITUENTS

Long-range cross-ring reactions occur when (M - H)(-) ions of methoxy- and ethoxy-C6H4-(-)NCOR (R = H, CH3, C6H5 and CH3O) are subjected to collisional activation, These reactions are generally minor processes: a particular example is the cross-ring elimination p-C2H5O-C6H4-(NCOC H3)-N-- --> [CH3-(p-C2H5O-C6H4-NCO)] --> p-(O--)-C6H4-NCO + C2H4 + CH4 . Major processes of these (M - H)(-) ions involve (i) losses of radic als to form stabilised radical anions, e.g. (a) loss of a ring H-. or (b) CH3. (or C2H5.) from the alkoxy group, and (ii) proximity effects when the two substituents are ortho, e.g. loss of CH3OH from o-CH3O-C6 H4-(NCHO)-N-- yields deprotonated benzoxazole. Another fragmentation o f an arylmethoxyl anion involves loss of CH2O. It is proposed that los ses of CH2O are initiated by anionic centres but the actual mechanisms in the cases studied depend upon the substitution pattern of the meth oxyanilide: o- and p-methoxyanilides may undergo ipso proton transfer/ elimination reactions, whereas the in-analogues undergo proton transfe r reactions to yield an o-CH3O substituted aryl carbanion followed by proton transfer from CH3O to the carbanion site with concomitant loss of CH2O.