nucleophiles(亲核试剂 g a a nucleophile is a reagent that seeks a o positive center. (The word nucleophile comes from nucleus, the positive part of an atom, E. plus-phile from the Green word philos meaning to love. )When a nucleophile reacts e with an alkyl halide, the positive center that the nucleophile seeks is the carbon atom that bears the halogen atom. this carbon atom carries a partial positive charge because the electronegative halogen pulls the electrons of the carbon-halogen bond in its direction C→>Ⅹ
Organic Chemistry Organic Chemistry Xiamen Xiamen University University Nucleophiles (亲核试剂 ) A nucleophile is a reagent that seeks a positive center. (The word nucleophile comes from nucleus, the positive part of an atom, plus –phile from the Green word philos meaning to love.) When a nucleophile reacts with an alkyl halide, the positive center that the nucleophile seeks is the carbon atom that bears the halogen atom. This carbon atom carries a partial positive charge because the electronegative halogen pulls the electrons of the carbon-halogen bond in its direction. C > X δ + δ −
Leaving groups(离去基团) a to be reactive-that is to be able to act as s the substrates in a nucleophilic substitution U. reaction-a molecule must have a good leaving group. In alkyl halides the leaving group is the halogen substituent-it leaves as a halide ion. To be a good leaving group a the substituent must be able to leave as a relatively stable, weakly basic molecule or ion. Because halide ion are relatively stable a and are very week bases, they are good g leaving groups
Organic Chemistry Organic Chemistry Xiamen Xiamen University University Leaving groups (离去基团 ) To be reactive that is, to be able to act as the substrates in a nucleophilic substitution reaction a molecule must have a good leaving group. In alkyl halides the leaving group is the halogen substituent it leaves as a halide ion. To be a good leaving group the substituent must be able to leave as a relatively stable, weakly basic molecule or ion. Because halide ion are relatively stable and are very week bases, they are good leaving groups
卤代烃的活泼性: CH,X CHO-CHX Chr choCho> CH2-CHCH,X RI> RBr>rcl
Organic Chemistry Organic Chemistry Xiamen Xiamen University University 卤代烃的活泼性 卤代烃的活泼性: CH 2 X CH 2 CHCH 2 X CH 3CH 2CH 2 X CH 2 CHX X > > R I > R B r > R C l
卤素交换反应 Nal RBr(Cl) RI+NaBr 丙酮 卤代烃与硝酸银的反应 AgNO R一X Etoh R-ONOh +AgX 用于鉴别伯、仲、叔卤代烃
Organic Chemistry Organic Chemistry Xiamen Xiamen University University 卤素交换反应 R B r (Cl) Na I 丙酮 R I + N aBr 卤代烃与硝酸银的反应 R X R ONO2 + AgX AgN O 3 Et O H 用于鉴别伯 仲 叔卤代烃
CHoCI 室温 加热 CHo-CHCHoCI AgC↓立即 云( CH3)3CCI (CH3)2CHCI AgNO3AgCl↓稍慢 EtOH Ch CHoCHoCI AgC cD CH,=CHCI CI
Organic Chemistry Organic Chemistry Xiamen Xiamen University University CH 2Cl (C H 3 ) 3CCl CH 2 CHCH 2Cl (C H 3 ) 2CHCl CH 3CH 2CH 2Cl CH 2 CHCl Cl AgN O 3 EtOH A gCl 立即 A gCl 稍慢 AgC l 室温 加热