Additivity of the proton affinity of polysubstituted benzenes: the ipso position

✍ Scribed by Zvonimir B. Maksić; Mirjana Eckert-Maksić; Martin Klessinger

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 363 KB
• Volume: 260
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(96)00900-1

✦ Synopsis

It is shown, by the MP2(fc)/6-31G * *//HF/6-31G* + ZPE(HF/6-31G*) theoretical model and concomitant use of homodesmic reactions, that the ipso proton affinities in polyfiuorinated benzenes follow a simple additivity rule. Performance of the latter is good, as evidenced by a low average absolute deviation Aab ~ = 0.8 kcal/mol from the accurate ab initio results. Additional evidence supporting the additivity concept is provided by good accordance with the experimental proton affinity (PA) for perfluorobenzene. The present approach enables estimates of the ipso PAs of multiply substituted aromatics. It is particularly useful in those systems which involve atoms or atomic groupings with lone pairs of electrons proximate to the aromatic 7r moiety. The additivity rule of thumb offers a simple rationalization of the ipso proton affinities. The origin of the PA additivity is briefly discussed.