Fragmentation reactions of some deprotonated acetophenones

✍ Scribed by Swapan K. Chowdhury; Alex. G. Harrison

• Book ID: 102965847
• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 596 KB
• Volume: 25
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210251203

✦ Synopsis

The collision-induced dissociation reactions of the enolate ions, [ XSH,COCD,] -, derived from labelled acetophenone and the fluoro-. chloro-and nitro-substituted acetophenones, were studied as a function of collision energy over the range 5-100 eV on the laboratory scale, enabling breakdown graphs to be established. For the acetophenone and fluoroacetophenone enolates the major primary fragmentation reaction forms [ XGH.1-+ D,CCO, although the formation of XC,H,D + [ DCCOlis favoured thermochemically. This result implies that there is a significant energy barrier for D+ abstraction in the [ XSH,]--D,CCO ion-dipole complex formed initially on collisional activation of the enolate. The ortho-and metu-fluorophenyl anions fragment further by elimination of HF. By contrast, cblorophenyl anions show no loss of HCI hut may fragment to form C1-. In addition, C1is formed from the chloroacetophenone enolate ions at low collision energies, possibly by a displacement reaction of [ DccOlon the chlorobenzene before theCiC,H,D-( DCCOjion-dipole complex separates. The lowest energy fragmentation channel for the uitro-substituted enolate ions is elimination of NO. At higher collision energies the nitrophenyl anion is formed and itself fragments to form NOz-; this reaction appears to be particularly facile for the ortho isomer. In a number of cases exchange of hydrogen between the ring and the enolic position is observed, particularly at low collision energies. A pronounced effect of collision gas identity on the breakdown graph for acetophenone enolate is reported and possible origins are discussed.