Schindele Claus, Houk K N, Mayr Herbert
Contribution from the Department Chemie der Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13 (Haus F), D-81377 München, Germany.
J Am Chem Soc. 2002 Sep 18;124(37):11208-14. doi: 10.1021/ja020617b.
Quantum chemical calculations of the affinities of benzhydryl cations (XC(6)H(4))(2)CH(+) for the methyl anion, hydroxide, and hydride anion have been performed up to the B3LYP/6-311++G(3df,2pd)//B3LYP/6-31G(d,p) level and compared with rate and equilibrium constants in solution. An excellent linear correlation between the empirical electrophilicity parameter E (by log k = s(N + E); Mayr, H.; Bug, T.; Gotta, M. F.; Hering, N.; Irrgang, B.; Janker, B.; Kempf, B.; Loos, R.; Ofial, A. R.; Remennikov, R.; Schimmel, H. J. Am. Chem. Soc. 2001, 123, 9500-9512) and the calculated methyl anion affinities ranging over 46.5 kcal mol(-1) is found that reproduces the electrophilicity parameters E which range from -10 to +6 with a standard deviation of +/-0.26 (11 points). The calculated OH(-) and H(-) affinities correlate with the calculated CH(3)(-) affinities with a slope of 1.00, indicating that the relative anion affinities of benzhydrylium ions are independent of the nature of the reference base. Linear correlations of the experimental pK((R)(+)) values and chloride ion affinities in solution with the calculated anion affinities in the gas phase indicate that solvation attenuates the differences of carbocation stabilization in the gas phase but does not affect the relative differences. Application of Marcus theory shows that only reaction series with alpha = partial differential DeltaG(++)/ partial differential Delta(r)G degrees = 0.5 corresponding to a slope parameter of s = 0.67 can have constant intrinsic barriers. The slope parameters s found for pi-nucleophiles and C-H hydride donors (s approximately equal 1) are interpreted by a decrease of the intrinsic barriers with increasing electrophilicities of the carbocations. On the other hand, a value of s < or = 0.67 as found for many n-nucleophiles as well as for Si-H, Ge-H, or Sn-H hydride donors is indicative of intrinsic barriers which are constant or slightly increase with increasing electrophilicity of the carbocation.
对二苯甲基阳离子(XC₆H₄)₂CH⁺与甲基阴离子、氢氧根离子和氢负离子的亲和力进行了量子化学计算，计算水平高达B3LYP/6 - 311++G(3df,2pd)//B3LYP/6 - 31G(d,p)，并与溶液中的速率和平衡常数进行了比较。经验亲电参数E（通过log k = s(N + E)；迈尔，H.；布格，T.；戈塔，M. F.；赫林，N.；伊尔冈，B.；扬克，B.；肯普夫，B.；洛斯，R.；奥菲亚尔，A. R.；雷门尼科夫，R.；施密尔，H. J. Am. Chem. Soc. 2001, 123, 9500 - 9512）与计算得到的甲基阴离子亲和力在46.5 kcal mol⁻¹范围内呈现出极好的线性相关性，该相关性重现了亲电参数E，其范围从 - 10到 + 6，标准偏差为±0.26（11个点）。计算得到的OH⁻和H⁻亲和力与计算得到的CH₃⁻亲和力的斜率为1.00，表明二苯甲基离子的相对阴离子亲和力与参考碱的性质无关。实验pK(R⁺)值和溶液中氯离子亲和力与气相中计算得到的阴离子亲和力的线性相关性表明，溶剂化减弱了气相中碳正离子稳定性的差异，但不影响相对差异。马库斯理论的应用表明，只有α = ∂ΔG⁺⁺/∂ΔrG° = 0.5（对应斜率参数s = 0.67） 的反应系列才可能具有恒定的内在势垒。对于π亲核试剂和C - H氢化物供体发现的斜率参数s（s约等于1）可以解释为随着碳正离子亲电性的增加，内在势垒降低。另一方面，对于许多n亲核试剂以及Si - H、Ge - H或Sn - H氢化物供体发现的s ≤ 0.67的值表明内在势垒是恒定的，或者随着碳正离子亲电性的增加略有增加。
