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卤化硼BX_3为缺电子化合物,它们都是已知的强Lewis酸.然而关于BX_3的相对酸强度,却是一个颇有争议的问题.本文拟对此进行探讨.三卤化硼为平面三角形分子,考虑空间效应和诱导效应,可知作为Lewis酸其相对强度为:BF_3>BCl_3>BBr_3这是因为:1、随着原子序数的递增,氟、氯、溴、碘离子半径依次增大,由于空间障碍,使得中心硼原子接受电子对的能力减弱;2、考虑卤素的相对电负性,简单的取代基诱导效应(由于抽回σ电子云密度而减弱了对硼核电荷的屏蔽,使中心原子硼的有效核电荷增加)也会使我们予期BF_3是BX_3系列中最强的Lewis酸.
However, the relative acid strength of BX_3 is a very controversial issue.This paper intends to discuss this matter.Br trihalide is a planar triangular molecule, Considering the space effect and the induction effect, we can see that the relative intensity of Lewis acid is: BF_3> BCl_3> BBr_3 This is because: 1, with the atomic number increasing, the radius of fluorine, chlorine, , So that the ability of the central boron atom to accept electron pairs weakens. 2. Considering the relative electronegativity of halogens, a simple substituent-induced effect (due to the withdrawal of the σ electron cloud density weakened the shielding of the boron core charge, the central atom boron The effective nuclear charge increase) will also make us expectation BF_3 is the strongest Lewis acid in the BX_3 series.