Comparison of ΔG°Acid (gas phase) and kinetic acidities measured in methanolic sodium methoxide
✍ Scribed by Heinz F. Koch; Justin C. Biffinger; Masaaki Mishima; Mustanir; Gerrit Lodder
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 104 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0894-3230
No coin nor oath required. For personal study only.
✦ Synopsis
Hydron exchange rates, k exc (M À1 s À1 ), using methanolic sodium methoxide were compared with DG°A cid , (kcal mol À1 ) (gas phase) for 9-phenylfluorene, C 6 H 5 CH(CF 3 ) 2 , m-CF 3 C 6 H 4 CH(CF 3 ) 2 , p-CF 3 C 6 H 4 CHClCF 3 , m-CF 3 C 6 H 4 CHClCF 3 , 3,5-(CF 3 ) 2 C 6 H 3 CHClCF 3 , fluorene and C 6 F 5 H. There is a good linear correlation for p-CF 3 C 6 H 4 CHClCF 3 , m-CF 3 C 6 H 4 CHClCF 3 and 3,5-(CF 3 ) 2 C 6 H 3 CHClCF 3 , with the others falling off the line. The fluorinated benzyl compounds and pentafluorobenzene have near-unity isotope effects and therefore differ from the fluorenyl compounds. Although the acidity and the exchange rates for three of the compounds [9phenylfluorene, C 6 H 5 CH(CF 3 ) 2 and p-CF 3 C 6 H 4 CHClCF 3 ] are similar, the important proton-transfer step to form a hydrogen-bonded carbanion intermediate and the subsequent breaking of that weak bond to form a free carbanion in methanol differ significantly for the fluoernyl compound compared with the two fluorinated benzylic compounds.