N-苄叉基-2-氨基噻唑及其类似物的构象和分子内的扭曲驱动力  

The Conformation of N-Phenylmethylene-2-thiazoleamine Species and the Driving Forces for Twisting Molecule

作　　者：虞忠衡[1] 宣正乾[1] 郭彦伸[1] 彭晓琪 王桐信[1] 金祥林[2] 

机构地区：[1]中国科学院化学研究所 [2]北京大学化学与分子工程学院

出　　处：《高等学校化学学报》2001年第1期122-126,共5页Chemical Journal of Chinese Universities

基　　金：国家自然科学基金!(批准号 :2 9872 0 42 );国家重点基础研究发展规划项目!(批准号 :G19980 10 10 0 )资助

摘　　要：确定了 N-苄叉基 -2 -氨基噻唑 ( 2 a)和 N-对硝基苄叉基 -2 -氨基噻唑 ( 2 b)的晶体结构 .结合已报道的N -对硝基苄叉基 -2 -氨基嘧啶 ( 1 a) ,N -对硝基苄叉基 -2 -氨基吡啶 ( 1 b)和 N -苄叉基 -3-氨基吡啶 ( 2 c)的晶体结构 ,利用 AM1 ,RHF,DFT方法和 6-31 1 G,6-31 1 G* * 基组 ,优化每个分子的 2 2个旋转构象 (θ=0°～ 90°) .由 DFT法所得到的最优构象的扭角 θ( 1 a,2 2°;1 b,0°;1 c,4 2°;2 a、 2 b:0°)与实验值 ( 1 a,2 6°;1 b,2 0°;1 c,4 6°;2 a,8.8°;2 b,3.8°)最接近 .尽管分子最优构象扭角的差异很大 ,但总电子能最稳定的构象都在 θ=±4 2°附近 .在任一分子、任何电子态中 ,离域的 π体系总是失稳定的 ,全平面构象不是 π体系最稳定的构象 .无论是离域的还是定域的π体系 ,它们均倾向于扭曲的几何构象 .π电子的离域是分子扭曲的驱动力之一 .与经典观点相反 ,非键原子间的核排斥作用是分子扭曲的阻力 ,而不是动力 .The crystal structures of N-phenylmethylene-2-thiazoleamine(2a) and N-[(4-nitrophenyl)methylene]-2-thiazoleamine (2b) were determined. Twenty-two rotational geometries(θ=0°~90°) of each of two molecules were optimized using AM1, RHF/6-311G~, B3LYP/6-311G and B3LYP/6-311G~. The twist angles of their preferential geometries obtained from DFT are both 0°, which are most close to the experimental values (2a, θ=8.9°; 2b, θ=3.9°) of all angles obtained from various optimized methods. Although there is a great difference in the twist angles of the five molecules, 2a, 2b, N-(4-nitrophrnyl)methylene-2-pyrimidineamine (1a), N-(4-nitrophenyl)methylene-2-pyridine-amine (1b) and N-phenyl)methylene-3-pyridineamine (1c ), their lowest total electronic energies occur in the optimized geometries with the similar twist angles which are in the region of θ from 37 to 42° and almost have nothing to do with the optimized methods (HF and DFT) and Gaussian basis sets. The π system in the geometry with θ=0° is destabilized no matter whether it is delocalized or not. It appears that the π system always prefers a twisted geometry. The driving force for out-of-plane twist of the molecules arises from the electronic interaction, and the nuclear repulsion is, practically, a resistance for distortion of molecule.

关 键 词：共轭效应 扭角驱动力 构象 N-苄叉基-2氨基噻唑 N-对硝基苄叉基-2-氨基噻唑 

分 类 号：O626.25[理学—有机化学] O621.13[理学—化学]