关于分子特征形状的理论——Ⅲ.分子形貌上指示反应的区位和立体选择性

Theory on the molecular characteristic contour(Ⅲ)——the indication of molecular regioselectivity and stereoselectivity via the molecular face

分子的区位和立体选择性在化学中被广泛应用,但理论上仍少见对两种概念的可视化和量化的方法.本文在分子特征形状理论暨分子形貌理论的框架下,应用密度泛函理论中Kohn-Sham单电子作用势等于第一电离能负值定义分子的内禀特征轮廓,将电子密度和位阻力映射在该轮廓上用于预测分子的区位和立体选择性.对于区位选择性,通过比较分子形貌和静电势两种方法发现,分子形貌理论指示的单体可能形成二聚体的角度更加接近从头算方法下二聚体的角度;对于立体选择性,展示分子空间位阻的区域,预测的结果与已报道的实验结果一致.总之,分子形貌理论结合位阻力获得的结果能够指示分子区位和立体选择性,对分子反应的位点进行预测和解释,可进一步探讨应用.

Chemical insights of a very wide application including regioselectivity and stereoselectivity are still rare in the visualization and quantification.The intrinsic characteristic contour of a molecule is defined as a contour at each point of which the Kohn-Sham one electron potential is equal to the negative value of the first ionization energy,then mapping the electron density on this contour defines a molecular face.It is shown that the electron density and steric force on the molecular face may be used to predict molecular regioselectivity and stereoselectivity intuitively and quantitatively.As for regioselectivity,the angles predicted by molecular face for monomers forming dimers are closer to the angles of dimers from ab initio calculation than those from electrostatic potential methods.And the steric force on the contour can show the regions of steric effect,which is in agreement with experimental findings.In a word,the results can shed light on the molecular regioselectivity as well as stereoselectivity,and are insightful to predict and explain molecular reactive sites and orientation,which needs to be further studied in not distant future.