CAJ | 학술논문

确定了N-苄叉基-2-氨基噻唑(2a)和N-对硝基苄叉基-2-氨基噻唑(2b)的晶体结构.结合已报道的N-对硝基苄叉基-2-氨基嘧啶(1a)，N-对硝基苄叉基-2-氨基吡啶(1b)和N-苄叉基-3-氨基吡啶(2c)的晶体结构.利用AM1，RHF，DFT方法和6-311G，6-311G**基组，优化每个分子的22个旋转构象(θ=0°～90°).由DFT法所得到的最优构象的扭角θ(1a，22°；1b，0°；1c，42°；2a、2b：0°)与实验值(1a，26°；1b，20°；1c，46°；2a，8.8°；2b，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=±42°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.
학정료N-변차기-2-안기새서(2a)화N-대초기변차기-2-안기새서(2b)적정체결구.결합이보도적N-대초기변차기-2-안기밀정(1a)，N-대초기변차기-2-안기필정(1b)화N-변차기-3-안기필정(2c)적정체결구.이용AM1，RHF，DFT방법화6-311G，6-311G**기조，우화매개분자적22개선전구상(θ=0°～90°).유DFT법소득도적최우구상적뉴각θ(1a，22°；1b，0°；1c，42°；2a、2b：0°)여실험치(1a，26°；1b，20°；1c，46°；2a，8.8°；2b，3.8°)최접근.진관분자최우구상뉴각적차이흔대，단총전자능최은정적구상도재θ=±42°부근.재임일분자、임하전자태중，리역적π체계총시실은정적，전평면구상불시π체계최은정적구상.무론시리역적환시정역적π체계，타문균경향우뉴곡적궤하구상.π전자적리역시분자뉴곡적구동력지일.여경전관점상반，비건원자간적핵배척작용시분자뉴곡적조력，이불시동력.
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.