FREE-RADICAL-CHEMISTRY-自由基化学讲义课件.pptx

1、 Lavoisier,1889:“基”的概念，如甲基这样的基团；Oswald，1896:自由基是不能分离的物质；Gomberg，1900：首次制备出稳定的所谓“三苯甲基”自由基；(C6H5)3CBr(C6H5)3C+2 Ag2C(C6H5)3+2 AgBr白色固体元素分析：证明白色固体并非六苯基乙烷黄色溶液白色固体无氧空气2(C6H5)3C(C6H5)3COOC(C6H5)3+O2白色固体2(C6H5)3C2(C6H5)3C+I2IChapter 9.Free Radical Chemistry1.The concept of free radical (C6H5)3C(C6H5)3C2C(C

2、6H5)3Gomberg认为：1968年，NMR技术C6H5C6H5H(C6H5)3Cbenzene(C6H5)3C2自由基：一类带有未配对电子的原子或分子：甲基自由基，NO中性自由基，带电荷的自由基HHHsp2Chapter 9.Free Radical Chemistry1.The concept of free radical Some representative organic free radicals Thermal HomolysisPbMe4(I)heating450 CMe-MeMePbMe4(II)heating450 CMe-MeMe+PbMe42.Radical pr

3、oduction Thermal Homolysis of Peroxy Compounds and AzoalkanesC2H5O OC2H52C2H5O(gas phase)134-185 oCEa 37.3 kcal/molH3CCO OCCH32CH3CO(benzene)55-85 oCEa 32.3 kcal/molOOOPhCO OCPh2PhCO(benzene)60-80 oCEa 33.3 kcal/molOOO(CH3)3COOH+O3(CH3)3COO-60 oC+HO+O2Ea 7 kcal/mol2.Radical production Thermal Homoly

4、sis of Peroxy Compounds and Azoalkanes66-72 oCH 31.2 kcal mol-1N N CCCH3CNCH3NCH3CH3CCNCH3CH3C2+N2+S +12.2 cal mol-1K-1+40-70 oCH 29.0 kcal mol-1N N CCCH3CH3C6H5H3CH3CC6H5CH3CH3CC6H52+N2+S +11 cal mol-1K-1+tolueneAIBN2.Radical production Relative reaction rate and activation parameters for some ther

5、mal homolysis processesreactionkrel/kJ mol-1 S/J K-1 mol-1RO-OR 2 ROR=MeR=t-BuR=MeCOR=PhCO 10.3160060 160165130139+45+45+48+12RN=NR 2 R+N2R=MeR=CF3R=i-PrR=t-BuR=CH2=CHCH2R=PhCH2R=Me2CCN 10.0690325007.7 x 106106very fast 240245180190156155125+78+59+11+76+17+17CH3-CH3 2 CH3 372+133 Photochemical Homol

6、ysisCl22 ClhvBr22 BrhvROClROhvRSSR2RShv+ClRONOROhv+NORONN ORROhv+N2sensitizer2RRORO+R+RCOhv2.Radical production Photochemical HomolysisOOOOC(CH3)3hv(CH3)3COthermally stable at room temperature(H3C)3CO O C(CH3)3(CH3)3CO2hv(CH3)3CO+(C2H5)3SiBr(CH3)3COH+(C2H5)3Si(C2H5)3Si+RBr(C2H5)3SiBrR+2.Radical prod

7、uction 2.Radical production Kolbe ReactionRCOO-RCOOR-e+CO2R2RR2 CH3O2C(CH2)8COO-eCH3O2C(CH2)18CO2CH32.Radical production birabical formationFClFClF2Cl2F2Cl2ABF2Cl2Cl2F2+bond rotationclosurebefore ratationclosureafter rotationFFXXRH biradical formationNNH3CH3CC2H5C2H5H3CH3CC2H5C2H5CH3CH3C2H5C2H5mesoC

8、2H5CH3CH3C2H5dl+hv or heatingNNH3CCH3hv or heatingH3CCH3+N2H3CO2CH3CO2CH3CCH3CO2CH3CO2CH3H3CCH3CO2CH3CO2CH3 Table.一些C-H键的均裂能（k J mol-1）分 子均裂能（k J mol-1）分 子均裂能（k J mol-1）H3CHH3CH2CH(H3C)2HCHC6H5H2CH423402385356F3CHHOH2CHH3COCH2CHCH2HNC444385385360H3CCCH3CH3H CCH3CH3H CHHFCFFCH2电子效应共振效应CH2CH2CH2CH23.T

9、he relative stability of the free radicals 立体效应：对自由的稳定化作用(H3C)3CC(CH3)3OC(CH3)3NOO(H3C)3CN C(CH3)3O可以真空蒸馏100oC加热100小时不分解，无限期保存对氧100oC还稳定能在实验室无限期保存立体效应和共轭效应的共同稳定化作用固体，空气中无限期稳定无氧时可在高温下无限期的存在The relative stability of the free radicals 其它一些稳定的自由基对氧稳定，能在空气中长期贮存固态无限期稳定，300oC是热稳定的可在溶液中长期保存ClClClClClClClClC

10、lClClClClClClNNNN实验条件下稳定，不同氧反应CHOOt-But-But-But-Bu Chemical methodN NO2NO2NNO2紫色RN NO2NO2NNO2colourlessR(DPPH)For unstable free radicalC6H5CHN C(CH3)3O+RC6H5HCN C(CH3)3ORstable radical4.Characterization of Free Radicals 4.Characterization of Free Radicals ESR(Electron Spin Resonace)(电子顺磁共振）intensity

11、magnetic field Ho电子自旋与核自旋的偶合：导致ESR谱的裂分n个等同的核，可以谱线裂分为2n x I+1个峰不同的核，I值不同，1H、13C、19F为1/2 2H、14N为1HHHHHH1:11:2:11:3:3:1electron-proton coupling:coupling constantHHHaa=2.3 x 10-3 T ESR(Electron Spin Resonace)(电子顺磁共振）未配对电子与几个不等同的核所共有时：OHHa2a2a1（2 x 1 x 1/2+1)x(2 x 1 x 1/2+1)=4a2a1H3COHCH3a2=7 x 10-5 Ta1=

12、1.97 x 10-3 TOHH（2 x 6 x 1/2+1)x(2 x 1 x 1/2+1)=14HNaHaN（2 x 1 x 1/2+1)x(2 x 1 x 1+1)=6 CIDNP(Chemically Induced Dynamic Nuclear Polarization)(化学诱导动态核极化）化学诱导动态核极化的一般原理1、正常情况下，中性分子处于磁场中，高能态的质子数目略低于低能态的质子数：NMR波谱的强度取决于高、低能态质子的数目；2、在自由基反应中，由于未配对电子和质子的相互作用，使自由基中的质子发生极化作用，进而导致高、低能态质子的数目的分布发生变化；3、即使是中间体自由基

13、已经变成抗磁性的稳定产物，这种质子的极化现象仍可保持若干分钟，这样，记录下来的被激化的质子的NMR图谱（CIDNP）表现出特殊的强度；4、若低能态中极化质子数目多，将有强的NMR吸收波谱；若高能态中极化质子数目多，在高频辐射影响下，处在高能态的极化质子将回到低能态，随之产生发射的NMR波谱（即负吸收）。4、Free radical reactions自由基反应的特点1、自由基反应即可在溶剂中进行，又可在气相中进行，规律相似，但由于溶剂笼效应，二者的选择性规律可能不同。2、自由基反应被典型的自由基源如光、高温或自由基引发剂加速。光引发时，量子产率可以很高，如可达到1000。3、自由基反应一般不被

14、酸碱所催化。4、自由基反应常被自由基抑制剂如氧化氮、分子氧、对苯二酚、有机胺以及苯醌等减慢。5、自由基反应均有诱导期，诱导期后可以产生链式反应，反应级数复杂，难以确定。6、芳香自由基取代不遵守定位规律。Chain ReactionsChain reactions can be divided roughly into two types:polymerizations and nonpolymerizations.Chain Reactions consist of three stages:initiation,propagation and termination.Each stage m

15、ay include one or more individual reactions;reaction schemes can become complex if a number of different radicals are present reacting in a variety of ways,including perhaps with products of the reaction.R CH2CbaH2CabnR CH2CbaH2Cabn+R CH2Cban+1RCH2Cban+1R CH2CbaH2CabnR CH2CbaCHabnR CH2CbaH2C CHabn+T

16、erminationPolymerization chain reactionsIn2 RH2CabR+R CH2CbaR CH2CbaH2Cab+R CH2CbaH2CabH2CabR CH2CbaH2CabCH2abetc.InitiationPropagation TerminationNonpolymerization chain reactionsInitiationPropagationRCH3CH3OClRCH3CH3OhvRCH3CH3OR+H3CH3CORRCH3CH3OCl+RClRCH3CH3O+R+RRR TerminationTelomerizationIn2 RH2

17、CCH2R+R CH2CH2InitiationChain growthCCl4R+R Clor+CCl3H2CCH2+Cl3CCH2CH2CCl3Chain transferCl3CCH2CH2nH2CCH2+Cl3CCH2CH2n+1Cl3CCH2CH2nCCl4+Cl3CCH2CH2nCl+CCl3Cl3CCH2CH2n2Cl3CCH2CH2n2Cl3CCH2CH2n+CCl3Cl3CCH2CH2nCCl3CCl32Cl3CCCl3 Radical SubstitutionsABCABC+AB+CH2SH2:abstractionABC+DDBCDABCA+(addition-elimi

18、nation)(1)HalogenationInXH RX+XHR+RXXR X+XR+R R+XRR XX2X2InitiationPropagationTermination (2)AutoxidationInRH RR+RO O+InitiationPropagationTerminationR+O2R+RO ORO O+RO OHRO ORO O2ROOOORRO2+O2ROORR=tertiaryRO O2+O2R=primaryCOOOOHHOHOH+(3)Aromatic SubstitutionR+RHYO2+YHRR+HOOIsomer distribution in aromatic substitutionX+XHYY+XHXHYYXXXYXYXYXHXHXHX+other pathwayother pathwaySee P.798-799 (3)Aromatic Substitution+CH3NO2NO2O2NNO2NO2O2NCH3+AdNO2NO2O2NAdNO2O2NAdNO2NO2NO2O2NRNO2NO2O2NR