Substituent effects on ion abundances and energetics in substituted acetophenones

✍ Scribed by Margaret S. Chin; A. G. Harrison

• Publisher: John Wiley and Sons
• Year: 1969
• Tongue: English
• Weight: 536 KB
• Volume: 2
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/oms.1210021106

✦ Synopsis

Based on the quasi-equilibrium theory of mass spectra it is shown that the intensity ratio [A]+/[M]+, where [A]+ is a fragment ion and [MI+ is the molecular ion, is given by [A]+/[M]+ = f' (k,/kt) ((l/f) -I), where f is the fraction of molecular ions with insufficient energy to fragment, f' is the fraction of [A]+ ions with insufficient energy to fragment, and kJkt is the fraction of fragmenting molecular ions which form [A]+. For substituted acetophenones it is shown that f depends on the substituent present and that f' k,/kt is also substitfient dependent for formation of both [CH,CO]+ and [YC,H,CO]+. It is also shown that no direct information concerning the effect of a substituent on the rate of a particular fragmentation reaction can be obtained from intensity studies.

The ionization potentials of the parent molecules and the appearance potentials of the [YC,FI,CO]+ fragment ions have been measured for fifteen substituted acetophenones and the correlations with substituent constants are discussed.