7143-79-5Relevant academic research and scientific papers
Steric and Electrochemical Effects on Rates of Electron Transfer and SN2 Reactions of 9-(Dialkylamino)fluorenide Ions with Alkyl Halides
Bordwell, F. G.,Harrelson, John A.
, p. 1052 - 1057 (2007/10/02)
Rate ratios for reactions of PhCH2Cl vs Ph2CHCl with seven 9-(dialkylamino)fluorenide (9-R2NFl(1-)) ions were measured in Me2SO solution.Although the reaction sites in these ions are known to be highly congested and Ph2CHCl is more sterically hindered than is PhCH2Cl, the kPhCH2Cl/kPh2CHCl rate ratios for reactions with 9-R2NFl(1-) ions in Me2SO were all much lower (0.20-4.9) than for the less hindered 9-MeFl(1-) or p-MeOC6H4O- ions (81 and 138, respectively).This suggested that the Ph2CHCl reactions with 9-R2NFl(1-) ions were occuring by single electron transfer(SET) mechanisms, despite the formation of high yields of SN2-type products.This conclusion was supported by the observation of a close correspondence between SET rates (log kSET), calculated by using the Marcus equation, and log kobsd for reactions of 2-R2NFl(1-) ions with both a known single electron acceptor, F3CCH2I, and with Ph2CHCl and (p-ClC6H4)2CHCl.Similar log kSET vs log kobsd comparisons for reactions of the 9-R2NFl(1-) ions with PhCH2Cl, c-C6H11Br, and n-BuBr revealed greater disparity.
Properties of Anions, Radicals, and Radical Cations Derived from 9-(Dialkylamino)fluorenes
Bordwell, F.G.,Cheng, Jin-Pei,Seyedrezai, S.E.,Wilson, Craig A.
, p. 8178 - 8183 (2007/10/02)
Equilibrium acidities for seven 9-(dialkylamino)fluorenes together with their oxidation potentials and those of their conjugate bases have been measured in Me2SO solution.These data are used to estimate (a) the homolytic bond dissociation energies, (BDEs) of the 9-C-H bonds in these molecules, (b) the acidities of the corresponding radical cations, and (c) the relative stabilities of the radicals formed on deprotonation of their radical cations.Comparisons are made with similar estimates of the effects of 9-(1-imidazolyl), 9-(3-methyl-1-pyrazolyl), 2-Me2N, and 2,7-(Me2N)2 groups.The 2-Me2N and 2,7-(Me2N)2 groups decrease the acidity of the fluorene radical cation by 18 and 24 kcal/mol, respectively but have little effect on the BDEs of the 9-C-H bonds.On the other hand, the 9-dialkylamino groups were found to lower the BDEs of the 9-C-H bonds by 5-12.8 kcal/mol relative to that of fluorene (79.5) and to decrease the acidity of the fluorene radical cation by an average of only 6.5 pKHA.+ units.The latter decreases are the net result of making bont Eox(HA) more negative (acid weakening) and Eox(A-) more negative (acid strengthening).By contrast, the 9-imidazolyl group weakens the 9-C-H bond by only 3.3 kcal/mol and increases the acidity of the corresponding radical cation by 3.6 pKHA.+ units, relative to that of fluorene.The Me3N+ moiety of 9-Me3NFlH+ increases the 9-C-H BDE by 5 kcal/mol.
