西北农林科技大学：《有机化学 Organic chemistry》课程教学课件（2009）Chapter 05 Nucleophiles and Electrophiles

Section E Nucleophiles and Electrophiles Definition:Nucleophiles and electrophiles Active Intermediates: Anions Cations ;Charged Species; ■Radicals Neutral inorganic species

College of Science Section E Nucleophiles and Electrophiles „Definition: Nucleophiles and electrophiles „Active Intermediates: zAnions ; Cations ;Charged Species; „Radicals „Neutral inorganic species

E1:Nucleophiles s and electrophiles ■1 Nucleophiles electron-rich molecules and react with electrophiles Nucleophile ("nucleus-loving")=Lewis base(electron-pair donor) ooften negatively charged and used as Na+ or K+salt ●symbolized as:Nu. ■Nucleophilic center OThe specific atom or region of the molecule which is electron rich

College of Science E1: Nucleophiles and electrophiles „1 Nucleophiles zelectron-rich molecules and react with electrophiles zNucleophile (“nucleus-loving”) = Lewis base(electron-pair donor) zoften negatively charged and used as Na+ or K + salt zsymbolized as :Nu¯. „Nucleophilic center zThe specific atom or region of the molecule which is electron rich

o A nucleophile is a reagent that seeks a positive center. This is the positive The electronegative center that the halogen polarizes nucleophile seeks. the C-X bond o A nucleophile is any negative ion or any neutral molecule that has at least one unshared electron pair. HO: CHO:HS:CH3S CH3NH CN :I H,0 CH,OH CH3SH CH3NH2

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Nucleophiles The nucleophiles mostly are anions. HO:HS:: :N三C: etc. Not all nucleophiles are anions.Many are neutral. HOH CHgOH NH3 for example All nucleophiles,however,are Lewis bases

College of Science Nucleophiles The nucleophiles mostly are anions. – : : N C .. .. HS: .. – .. HO: – .. .. CH 3 O: – etc. Not all nucleophiles are anions. Many are neutral. .. .. HOH CH 3OH.. .. NH 3 : for example All nucleophiles, however, are Lewis bases

E1:Nucleophiles and electrophiles ■2 Electrophiles o electron-deficient molecules o can react with nucleophiles Electrophile ("electron-loving")=Lewis acid Electrophilic center othe specific atom or region of the molecule which is electron deficient ■symbolized as E+

College of Science E1: Nucleophiles and electrophiles „2 Electrophiles z electron-deficient molecules z can react with nucleophiles „Electrophile (“electron-loving”) = Lewis acid „Electrophilic center zthe specific atom or region of the molecule which is electron deficient „symbolized as E +

E2 Charged Carbon species 1 Anions Negatively charged ions with lone pairs of electrons are nucleophiles.The atom bearing the negative charge is the nucleophilic center 2 Cations Positively charged ions are electrophiles. The atom bearing the positivecharge is the electrophilic center. .carbocations:sp2(trigonal) geometry,planar,positive charge carbanions:sp3(tetrahedral) geometry,strong base,negative charge a Carbocation a Carbon Radical a Carbanion

College E2、 Charged Carbon speciesof Science „1 Anions Negatively charged ions with lone pairs of electrons are nucleophiles. The atom bearing the negative charge is the nucleophilic center „2 Cations Positively charged ions are electrophiles. The atom bearing the positivecharge is the electrophilic center. •carbocations: sp2 (trigonal) geometry,planar, positive charge • carbanions: sp3 (tetrahedral) geometry, strong base, negative charge

a Nucleophilic , Nucleophilic center .Nucleophilic center center 9 ：⊙ Fig.1.Examples of nucleophiles;(a)hydroxide ion;(b)carboxylate ion. Electrophilic Electrophilic a) center b) Electrophilic center H Fig.2. Examples of electrophiles:(a)carbocation;(b)allylic cation. a 0 b) Me2N C-H Me- Me Fig.3.(a)Dimethylformamide (DMF):(b)dimethylsulfoxide (DMSO)

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E3-1Nu:（亲核试剂与亲核性 Relative Nucleophilicity ■ 亲核性：在过渡态时对缺电子碳亲合能力（亲 近C+) ■碱性：与质子结合能力（亲近H+) 亲核能力： ■ RS>CN->I>NH3(NH2R )>RO (OH) >Br>PhO>CI》H20>F

College of Science E3-1 Nu: (亲核试剂与亲核性) Relative Nucleophilicity „亲核性：在过渡态时对缺电子碳亲合能力（亲 近C+） „碱性： 与质子结合能力（亲近H+） „亲核能力： RS->CN->I->NH3(NH2R )>RO- （OH-） >Br- >PhO- >Cl- 》H2O >F-

亲核试剂 亲核性是针对碳而言，其亲核性强弱往往受到 ■ 底物、溶剂甚至是浓度的影响。 ■比较亲核试剂的强弱在相同的底物和相同的反 应条件下比较： Nu CH3-Br Nu-CH3 Br Nu= H2O CH3CO2 NH3 CI OH CHO· CN HS relative reactivity 500 700 1,00016,00025,000100,000 125,000 Less reactive More reactive

College 亲核试剂 of Science „亲核性是针对碳而言，其亲核性强弱往往受到 底物、溶剂甚至是浓度的影响。 „比较亲核试剂的强弱在相同的底物和相同的反 应条件下比较： Nu - Nu - CH 3 + Br - + CH 3 - Br Nu = H2O CH3CO2- NH3 Cl - OH - CH3O - I - CN - HS - relative reactivity 1 500 700 1,000 16,000 25,000 100,000 125,000 More reactive Less reactive

Nucleophilicity(亲核性) CH3CO2CI->F- Anions are more nucleophilic than neutral compounds ■The solvent matters！

College Nucleophilicity(亲核性 of Science ) „CH 3CO 2 - Cl - > F - „Anions are more nucleophilic than neutral compounds „The solvent matters!