卤素离子与卤代苯气相S_NAr反应理论研究  

Theoretical Studies on the Gas-Phase S_NAr Reactions of Halobenzenes and Halide Anions

作　　者：李强根[1] 毛双[1] 蔡皖飞[1] 郑妍[1] 刘柳斜[1] 

机构地区：[1]四川师范大学化学与材料科学学院,成都610068

出　　处：《化学通报》2016年第5期418-424,共7页Chemistry

基　　金：四川省教育厅基金项目(13ZB0160)资助

摘　　要：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 reactions of halobenzenes and halide anions（ Ar Y ＋ X-= Ar X ＋ Y-,X,Y= F,Cl,Br and I） were investigated by the B3 LYP and MP2 methods with the 6-311 ＋ G ＊＊ basis set. Calculated results indicate that the SNAr reactions of halobenzenes and halide anions in the gas-phase proceed via a concerted mechanism,while a two-step addition-elimination pathway is founded with the formation of a stable σ-complex for X= Y = F. In view of thermodynamics and kinetics,the gas-phase SNAr reactions of halobenzenes attacked by fluoride ion are easy to proceed（ overall barrier ΔGb= 9. 0 ~ 17. 3 k J / mol）,whereas it would be hardly possible to observe the reactions for X = Cl-,Br-and I-due to the higher overall barriers（ ΔGb= 91. 3 ~ 202. 5 k J / mol）. In addition,the reactivities of the titled reactions can be analyzed by proton affinity（ PA）,the highest occupied orbital energy（ EHOMO） and Mulliken electronegativity（ χ） of the halide as well as the Wiberg bond order（ BO） and NPA charges（ Q）. The break of the C─Y bond in transition state（ TS） is mainly responsible for the reaction barriers,and the nucleophilicity of the halide anion is mainly dominated by EHOMO,while the leaving-group ability of halogen anion is governed by PA or χ.

关 键 词：SNAr反应 亲核试剂 反应性 B3LYP 反应机理 

分 类 号：O621.25[理学—有机化学] O643.12[理学—化学]