AlicyclicsAliphatic compounds containing rings, cycloalkanes, .ppt

1、Alicyclics Aliphatic compounds containing rings, cycloalkanes, cycloalkyl halides, cycloalkyl alcohols, cyclic ethers, cycloalkenes, cycloalkadienes, etc.,Cycloalkanes,cyclopropane cyclobutane cyclopentane cyclohexane,methylcyclopentane 1,1-dimethylcyclobutane,trans-1,2-dibromocyclohexane,cyclopente

2、ne 3-methylcyclohexene 1,3-cyclobutadiene,1,2,3,4,5,6,cycloalkenes,cyclohexanol ethyl cyclopentyl ether cyclohexyl alcohol,Cycloalkanes, syntheses:Modification of a ring compound:1. reduction of cycloalkene2. reduction of cyclic halidea) hydrolysis of Grignard reagentb) active metal & acid3. Corey H

3、ouse B. Ring closures,A. Modification of a cyclic compound:,H2, Ni,Sn, HCl,Mg; then H2O,Li,CuI,+ CH3CH2-Br,CH2CH3,must be 1o,Corey-House,ring closuresCH2=CH2 + CH2CO, hv Br-CH2CH2CH2CH2CH2-Br + Zn etc.,cycloalkanes, reactions: halogenation2. combustion 3. cracking 4. exceptions,Cl2, heat,+ HCl,excep

4、tions:H2, Ni, 80oCH3CH2CH3Cl2, FeCl3Cl-CH2CH2CH2-ClH2O, H+ CH3CH2CH2-OHconc. H2SO4 CH3CH2CH2-OSO3HHI CH3CH2CH2-I,exceptions (cont.)+ H2, Ni, 200o CH3CH2CH2CH3?,internal bond deviation heat of angles from 109.5 combustion60o -49.5o 166.690o -19.5o 164.0108o -1.5o 158.7,Cyclopropane undergoes addition

5、 reactions that other cycloalkanes and alkanes do not. This is because of angle strain in the small ring. Because the bond angles are less than the optimal 109.5o for maximum overlap, the bonds are weaker than normal carbon-carbon single bonds and can be added to. Cyclobutane has angle strain that i

6、s less than that for cyclopropane, reacts with H2/Ni at a higher temperature, but does not react like cylcopropane in the other exceptional reactions.,internal bond deviation heat of angles from 109.5 combustion60o -49.5o 166.690o -19.5o 164.0108o -1.5o 158.7120o +11.5o 157.4128.5o +19o 158.3135o +2

7、5.5o 158.6,Cyclohexane does not have any angle strain! It isnt a flat molecule. By rotating about the carbon-carbon bonds, it can achieve 109.5o bond angles.,chair twist boat,boat,conformations of cyclohexane,The chair conformation of cyclohexane is free of both angle strain and torsional strain (de

8、viation from staggered). This is the most stable conformation.,The boat conformation is free of angle strain, but has a great deal of torsional strain (eclipsed). To relieve the strain, it twists slightly to form the twist boat:,a = axial positions in the chair conformation e = equatorial positions,

9、CH3 in axial position CH3 in equatorial positionis more stable,Cycloalkenes, syntheses:Modification of a ring compound:1) dehydrohalogenation of an alkyl halide2) dehydration of an alcohol3) dehalogenation of vicinal dihalides(B. Ring closures),KOH(alc),H+, ,Zn,cyclohexene,Cycloalkenes, reactions: a

10、ddition of H2 10. hydroboration-oxid. addition of X2 11. addition of free radicals addition of HX 12. polymerization addition of H2SO4 13. addition of carbenes addition of H2O,H+ 14. epoxidation addition of X2 + H2O 15. hydroxylation dimerization 16. allylic halogenation alkylation 17. ozonolysis ox

11、ymerc-demerc. 18. vigorous oxidation,trans-1,2-dibromocyclohexane,H2, Pt,Br2, CCl4,HBr,H2SO4,H2O, H+,Markovnikov orientation,Br2 (aq.),H+, dimer.,HF, 0o,HBr, peroxides,polymerization,CH2CO, h,Peroxybenzoic acid,cis-1,2-cyclohexanediol,trans-1,2-cyclohexanediol,KMnO4,HCO3H,Br2, heat,stereoselective,c

12、yclic alcohols, halides, ethers as expected:,PBr3,Na,CH3COOH +,H+,NaOCl,NaOH,2o alkyl halide = E2,Mg,H2O,conc. HI, heat,1,4-dioxane,conc. HBr, heat,2 Br-CH2CH2-Br,Alicyclic compounds are chemically like their open chain analogs. The exceptions are for small ring compounds where angle strain may give

13、 rise to reactions that are not typical of other molecules.,Epoxides:,ethylene oxide propylene oxide cyclopentene oxide(oxirane) (methyloxirane),C6H5CO3H,Synthesis:,-butylene oxide,cis-2-butene,epoxides, reactions: acid catalyzed addition,H2O, H+,CH3CH2OH, H+,HBr,OH CH2CH2 OH,OH CH3CH2-O-CH2CH2,OH C

14、H2CH2 Br,OH CH2CH2 OH,CH3CH2-O-CH2CH2-OH,H2N-CH2CH2-OH,CH3CH2CH2CH2-OH,2. Base catalyzed addition,mechanism for acid catalyzed addition to an epoxide,mechanism for base-catalyzed addition to an epoxide:,acid catalyzed addition to unsymmetric epoxides?,OH + H2O, H+ CH3CHCH2OH,which oxygen in the prod

15、uct came from the water?,+ H218O, H+ ,18OH CH3CHCH2OH,CH3O + CH3OH, H+ CH3CHCH2OH,Br + HBr CH3CHCH2OH,Base?,18OH + Na18OH, H218O CH3CHCH2OH,NH2 + NH3 CH3CHCH2OH,OCH3 + CH3OH, CH3ONa CH3CHCH2OH,Acid:,Base:,Z + HZ CH3CHCH2OH,Z + Z-, HZ CH3CHCH2OH,“variable transition state”Z acid: C C OH,+,+,base:,Z C

16、 C O,-,Bond breaking is occurring faster than bond making, making the carbon slightly positive. C + : 3o 2o 1o,Bond breaking is occurring at the same time as bond breaking, there is no charge on the carbon. Steric factors are most important: 1o 2o 3o,Acid:,Base:,Z + HZ CH3CHCH2OH,Z + Z-, HZ CH3CHCH2OH,C+: Z to 2o carbon,steric factors: Z to 1o carbon,