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Comparison of Δ G ° Acid (gas phase) and kinetic acidities measured in methanolic sodium methoxide
Author(s) -
Koch Heinz F.,
Biffinger Justin C.,
Mishima Masaaki,
Lodder Gerrit
Publication year - 1998
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199808/09)11:8/9<614::aid-poc46>3.0.co;2-8
Subject(s) - chemistry , carbanion , sodium methoxide , methoxide , fluorene , methanol , medicinal chemistry , kinetic isotope effect , gas phase , hydrogen bond , inorganic chemistry , organic chemistry , deuterium , molecule , physics , quantum mechanics , polymer
Hydron exchange rates, k exc ( M −1 s −1 ), using methanolic sodium methoxide were compared with Δ G ° Acid , (kcal mol −1 ) (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 [9‐phenylfluorene, 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. © 1998 John Wiley & Sons, Ltd.