(CH_3)_2N和(CH_3)_2NH^+的密度泛函理论计算

Calculation of (CH_3)_2N and (CH_3)_2NH^+ by Density Functional Theory

用密度泛函理论UB3LYP／6-31G（d，p）方法研究了二甲胺自由基（CH3）2N及其质子化离子（CH3）2NH+的构象和超精细结构．在由构象研究得到的两种自由基的最稳定结构上，用密度泛函的UB3LYP和UB3PW91方法及从头计算的UHF、UMP2（FULL）方法计算了α-质子、β-质子和N核上的超精细偶合常数A（Hα）、A（Hβ）和A（N）结果表明：两种自由基中甲基内旋转的位垒均很低，分别为0．46kJ·mol-1（（CH3）2NH+）和2．6kJ·mol-1（（CH3）2N）．UB3LYP／6-31G（d,p）和UB3PW91／6-31G（d,p）计算的A（Hα）、A（Hβ）和A（N）与ESR实验结果符合得很好，UMP2／6-31G（d,p）方法的计算值与实验值符合得也较好．

Conformations and hyperfine structures of the dimethylamino radical (CH_3)_2N and its Protonated cation radical (CH3)2NH+ were studied at the UB3LYP/6-31G(d p) level, and isotropic hyperfine coupling constants on the α-proton, β-proton, and nitrogen nucleus (A(Hα), A(Hβ)and A(N)) of the two radicals were calculated using two DFT (UB3LYP and UB3PW91) methods and ab initio UHF and UMP2 (FULL) methods. The results of calculation indicate that the barriers to methyl group rotation in the two radicals are very low, being 0.46 and 2. 6 kJ·mol-1 for (CH3)2NH+ and (CH3)2N, respectively. The A (Hα), A(Hβ) and A(N) values in the two radicals are predicted by the UB3LYP/6-31G(d, p) and UB3PW91/6-31G(d, p) calculations in excellent agreement with experimental ones, and the UMP2 (FULL) /6-31G (d, p ) values are in quite good agreement with the experimental values.