文献类型：期刊文献

英文题名：Equilibrium Acidities and Homolytic Bond Dissociation Enthalpies of the Acidic C-H Bonds in Phosphonates and Related Phosphorus Containing Compounds

作者：Qi, Chenze[1];Du, Yijun;Lu, Yueqing;Sun, Xudong;Zhang, Xian-Man

机构：[1]Shaoxing Univ, Inst Appl Chem, Hangzhou 312000, Zhejiang, Peoples R China; Shaoxing Univ, Dept Chem, Hangzhou 312000, Zhejiang, Peoples R China

年份：2009

卷号：74

期号：21

起止页码：8078

外文期刊名：JOURNAL OF ORGANIC CHEMISTRY

收录：SCI-EXPANDED(收录号：WOS:000271113400008)、、EI(收录号：20094612448761)、Scopus(收录号：2-s2.0-70350741286)、WOS

基金：We greatly appreciate the kind help and stimulating discussions of Professor F G Bordwell of Northwestern University. We also appreciate the financial Support from the Natural Science Foundation of Zhejiang province, China.

语种：英文

外文关键词：Acidification - Dissociation - Electrostatics - Enthalpy - Polarization

外文摘要：The homolytic bond dissociation enthalpies (BDEs) of the acidic C-H bonds in it series of phosphonates and related phosphorus-containing Compounds have been determined by it combination (eq 3) of their equilibrium acidities (pK(HA)'s) and the oxidation potentials [E(ox)(A(-))'s] of their conjugate anions, which were measured in DMSO solution. The equilibrium acidity increases by 15.5, 14.9, and 10.9 pK units for the introduction of an alpha-P(O)(OEt)(2) group Into toluene, acetonitrile, and ethyl acetate, respectively. Comparison with the published equilibrium acidity increases by 25.6, 24.4, and 21.0 pK units for the introduction of an alpha-(+)PPh(3) group into the same series of substrates indicates that the phosphoryl carbanions (Horner-Wadsworth-Emmons reagents)are about 10 pK units more reactive than the corresponding triphenylphosphonium ylides (Wittig reagents). However, both alpha-P(O)(OEt)(2), and alpha-(+)PPh(3) groups have negligible effects oil the adjacent C-H BDEs, indicating that there is no resonance delocalization into the 3d vacant orbitals of phosphorus and that their acidifying effects are exclusively associated with the field/inductive (electrostatic) and polarizability effects. The acidifying effect of an alpha-CO(2)Et group is shown to be ca. 3 5 pK units stronger than that of an alpha-P(O)(OEt)(2) group in the same substrates, suggesting that the larger acidifying effect Of the alpha-CO(2)Et group Is predominantly associated with the resonance delocalization rather than with the field/inductive (electrostatic) and polarizability effects.