The mass spectra of intramolecularly hydrogen bonded 2(1 H )‐quinoxalinone and 2 H ‐1,4‐benzoxazin‐2‐one

The mass spectra of those 3‐phenacyl derivatives of 2(1 H )‐quinoxalinone and 2 H ‐1,4‐benzoxazin‐2‐one with an intramolecular hydrogen bonding showd that: (1) the primary elimination of the shole sidchain is reduced as compared with an unchelated derivative; (2) the importan t fragmentation routes in the quinoxalinone series are ring cleavage with loss of CO followed by recyclization and expulsion of a hydrogen atom, and this can also occur in the reverse order; (3) this reverse process is virtually absent in the benzoxazinone series. Finally, the doubly charged molecular ions appear to undergo an analogous decomposition giving fairly intense [M‐CO] 2+ or [M‐(CO+H or CI] 2+ ions.