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采用B3LYP/6-311+G**和MP2/6-311+G**方法,研究了卤素离子与卤代苯气相SNAr反应(Ar Y+X-=Ar X+Y-,X,Y=F,Cl,Br和I)。结果显示,气相里除了X=Y=F反应为分步路径外,其余反应通道都是协同SNAr机理;F离子进攻卤苯SNAr反应无论从动力学(总能垒ΔGb=9.0~17.3 k J/mol)还是热力学上来说都很容易进行,然而Cl、Br和I离子进攻的反应,其MP2吉布斯自由能垒(ΔGb)高达91.3~202.5 k J/mol,因此在气相里很难发生;另外,标题反应的反应性可以通过卤素离子质子亲和能(PA)、最高占据轨道能(EHOMO)、Mulliken电负性(χ)以及Wiberg键级(BO)与NPA电荷(Q)来分析,其中,过渡态里C─Y键的断裂是引起反应能垒升高的主要因素,亲核试剂的亲核能力主要由EHOMO控制,而卤素离子的离去能力由其PA或χ决定。
The gas phase SNAr reaction of halogen ions with halogenated benzene has been studied by the method of B3LYP / 6-311 + G ** and MP2 / 6-311 + G **. (Ar Y + X- = Ar X + Y-, X, Y = F, Cl, Br and I). The results showed that all the reaction channels were synergistic with SNAr except for the X = Y = F reaction in the gas phase. The results showed that the FNAs attacked the SNAr reaction of halobenzene in both kinetics (total energy barrier ΔGb = 9.0-17.3 kJ / mol) or thermodynamically. However, the attack of Cl, Br and I ion on the MP2 Gibbs free energy barrier (ΔGb) is as high as 91.3 ~ 202.5 kJ / mol and therefore hardly occurs in gas phase. In addition, the reactivity of the title reaction can be analyzed by halogen ion proton affinity (PA), highest occupied orbital energy (EHOMO), Mulliken electronegativity (χ) and Wiberg bond order (BO) and NPA charge (Q) Among them, the CY bond in the transition state is the main factor leading to the rise of the energy barrier. The nucleophilic ability of the nucleophile is mainly controlled by EHOMO, while the halide ion’s leaving ability is determined by its PA or χ.