Nucleophilic substitution reactions(亲核取代反应) The carbon-halogen bond of the substrate undergoes heterolysis, and the unshared pair of the nucleophile is used to form a new bond to the carbon atom Leaving group Nu R——X R Nu t Nucleophile Alkyl halide Product Halide ion 亲核试剂( Substrate底物) What is it reaction mechanism?
Nucleophilic substitution reactions（亲核取代反应） • The carbon-halogen bond of the substrate undergoes heterolysis, and the unshared pair of the nucleophile is used to form a new bond to the carbon atom Nu : - + R X R Nu + : - X Nucleophile 亲 核 试 剂 Alkyl halide (Substrate 底物) Product Halide ion Leaving group What is it reaction mechanism?
1S2 reaction(双分子亲核取代反应) lone step Nu.+ rX Nu R X Nur-R+ X transition state 过渡态 2 SI reaction(单分子亲核取代反应)( two steps) miting step n+ RX R+ X carbocation fast Nu R Nu R
Nu: - + RX Nu R X Nu R + X - 1. SN2 reaction (双 分 子 亲 核 取 代 反 应 )(one step) - - transition state 过 渡 态 2. SN 1 reaction (单 分 子 亲 核 取 代 反 应 )(two steps) RX R + + XLimiting step carbocation R + Nu: + - Nu R fast
6.5 Nucleophiles [nju kliefaill n.化]亲核试剂 a nucleophile is a reagent that seeks a positive center r This is the positive center The electronegative halogen that the nucleophile seek polarize the c-X bond
6.5 Nucleophiles [nju:kliefail] n.[化]亲核试剂 A nucleophile is a reagent that seeks a positive center X + - This is the positive center that the nucleophile seeks The electronegative halogen polarize the C---X bond
Specific Example HO"+CH3CH-Br-CH3CH2OH+ Br (SN2) cleo hile p ethanol Leaving group SIe (CH3)3C—c+H20 (CH3)3C++C(S1 Nucleophile fast (CH3)3C+ H,O (CH3)3C0——H tert-butyloxonium (CH3)3C—OH+H tert-butyl alcohol
Specific Example (CH3 ) 3 C Cl + H2 O (CH3 ) 3 C + (CH3 ) 3 C + + H2 O (CH3 ) 3 C O H H + (CH3 ) 3 C OH + H + (SN1) Nucleophile + Cl - tert-butyloxonium tert-butyl alcohol : Slow fast HO- + CH3 CH2 Br CH3 CH2 OH + Br - (SN2) Nucleophile ethanol Leaving group
65 a Leaving groups(离去基 团) To be a good leaving group the substituent must be able to leave as a relatively stable weakly basic molecule or ion Nu:+R—L∑R—Nu+:L 十 :NH3+CH3—-Br CH3--NH3 Br 十 Ch2 OH CH3 OH2 CH3OCH3 H2O H eaving group
6.5 A Leaving groups (离去基 团） To be a good leaving group the substituent must be able to leave as a relatively stable, weakly basic molecule or ion Nu: - + R L R Nu + :L - :NH3 + CH3 Br CH3 NH3 + Br + - CH3 OH2 + CH3 OH + Leaving group CH3 OCH3 + H2 O H +