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解释了“为什么R—X键离解能变化趋势不相同”的问题.R—X键离解能(BDE)可归因于3个主要因素:C—X固有健能,1,3成对排斥和分子内电荷-诱导偶极.当X原子给定,R—X(R=Me,Et,i-Pr,t-Bu)的BDE变化趋势由1,3成对排斥和分子内电荷-诱导偶极两个因素控制,前者减少R—X的BDE,后者增加或者减少R—X的BDE.在R—X为R—C键的系列化合物中(例如R—Me,R—CH==CH2,R—C≡≡CH,R—CN等),1,3成对排斥减少R—X的BDE,R—C键能变化趋势依R=Me,Et,i-Pr,t-Bu次序减小;对于X原子电负性小于C原子的R—X系列化合物(例如R—H,R—BH2,和R—SiH2等),上述两个因素均减小R—X的BDE,因而R—X键能变化趋势依R=Me,Et,i-Pr,t-Bu次序减小;对于X原子电负性大于C原子的R—X系列化合物(例如R—F,R—OH,R—Cl,R—Br,R—I,和R—NH2等),1,3成对排斥减少R—X的BDE,而分子内电荷-诱导偶极则增加R—X的BDE,于是R—X键能变化趋势取决于两者的竞争,结果表现为:(1)有的系列R—X键能变化依R=Me,Et,i-Pr,t-Bu次序增大(如R—F,R—OH等);(2)有的系列R—X键能变化依R=Me,Et,i-Pr,t-Bu次序减小(如R—I);(3)有的系列R—X键能变化依R=Me,Et,i-Pr,t-Bu次序变化很小(如R—Br).
Explains why the R-X bond dissociation can change in different directions. "The R-X bond dissociation energy (BDE) can be attributed to three main factors: C-X intrinsic fitness, 1,3 pairs (R = Me, Et, i-Pr, t-Bu). When the X atom is given, the BDE change trend of R-X (R = Me, Et, Induction dipole is controlled by two factors, the former decreases BDE of R-X, and the latter increases or decreases BDE of R-X. In the series of compounds where R-X is an R-C bond such as R-Me, R- = CH2, R-C≡≡CH, R-CN, etc.). The change trend of the BDE and R-C bonds of 1,3-exclusion reduction R-X is R = Me, Et, Order decrease; for the R-X series compounds (for example, R-H, R-BH2, and R-SiH2, etc.) whose X atom is less electronegative than C atom, both reduce the BDE of R- The order of R-X bond energy decreases as R = Me, Et, i-Pr and t-Bu. For R-X series compounds with electronegativity X of more than C atom, R-Cl, R-Br, R-I, and R-NH2, etc.), 1, 3 pair rejection repelling BDE of R-X while the intermolecular charge-induced dipole increases BDE of R- The tendency of the -X bond to change depends on the competition between the two , The results showed as follows: (1) Some series of R-X bond can be changed according to R = Me, Et, i-Pr and t- (3) some series of R-X bond can be changed according to R = Me, Et, i-Pr, t- , i-Pr, t-Bu sequence changes very little (such as R-Br).