Alicyclics - Organic Chemistry I - Lecture Slides, Slides of Organic Chemistry

Download Alicyclics - Organic Chemistry I - Lecture Slides and more Slides Organic Chemistry in PDF only on Docsity! Alicyclics Aliphatic compounds containing rings, cycloalkanes, cycloalkyl halides, cycloalkyl alcohols, cyclic ethers, cycloalkenes, cycloalkadienes, etc. docsity.com Cycloalkanes H2C H2C CH2 H2C H2C CH2 CH2 H2C H2C C H2 CH2 H2 C H2C H2C C H2 CH2 CH2 H2 C cyclopropane cyclobutane cyclopentane cyclohexane docsity.com cyclopentene 3-methylcyclohexene 1,3-cyclobutadiene 1 2 3 4 5 6 cycloalkenes docsity.com io 1D bicyclo[2.2.2]octane bicyclo[3.2.0]heptane ® docsity.com OH O CH2CH3 cyclohexanol ethyl cyclopentyl ether cyclohexyl alcohol docsity.com Br Li 2 CuLi Li CuI + CH3CH2-Br CH2CH3 must be 1o Corey-House docsity.com B. ring closures CH2=CH2 + CH2CO, hv  Br-CH2CH2CH2CH2CH2-Br + Zn  etc. docsity.com cycloalkanes, reactions: 1. halogenation 2. combustion 3. cracking 4. exceptions Cl Cl2, heat + HCl docsity.com internal bond deviation heat of angles from 109.5 combustion 60o -49.5o 166.6 90o -19.5o 164.0 108o -1.5o 158.7 docsity.com Cyclopropane undergoes addition 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 is less than that for cyclopropane, reacts with H2/Ni at a higher temperature, but does not react like cylcopropane in the other exceptional reactions. docsity.com internal bond deviation heat of angles from 109.5 combustion 60o -49.5o 166.6 90o -19.5o 164.0 108o -1.5o 158.7 120o +11.5o 157.4 128.5o +19o 158.3 135o +25.5o 158.6 docsity.com The chair conformation of cyclohexane is free of both angle strain and torsional strain (deviation from staggered). This is the most stable conformation. docsity.com 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: docsity.com Potential energy —> Conformer Conformer docsity.com O H HO H HO H OH OHH H OH O H HO H HO H H OHH OH OH CHO OHH HHO OHH OHH CH2OH beta-D-glucose alpha-D-glucose all groups equatorial one group forced to be axial more stable docsity.com Cycloalkenes, syntheses: A. Modification of a ring compound: 1) dehydrohalogenation of an alkyl halide 2) dehydration of an alcohol 3) dehalogenation of vicinal dihalides (B. Ring closures) docsity.com cor KOH alc) H*,A om Zn Or Br ae cyclohexene docsity.com H2C H2C C H2 CH C H2 C CH3 + HBr H2C H2C C H2 CH2 C H2 C CH3 3o carbocation Br H2C H2C C H2 CH2 C H2 C Br CH3 docsity.com Br OSO3H OH HBr H2SO4 H2O, H + Markovnikov orientation docsity.com OH Br + + Br2 (aq.) H+, dimer. HF, 0o docsity.com OH OH OH OH Br cis-1,2-cyclohexanediol trans-1,2-cyclohexanediol KMnO4 HCO3H Br2, heat docsity.com O3 H20,Zn See O=CHCH»CH»CH»CH»CH=O KMnQOzg, heat Ss HOsCCHsCHsCHsCH2CO2H ® docsity.com Br2 KMnO4 HCO3H Br HO OH HOBr OH anti syn anti stereoselective docsity.com Alicyclic compounds are chemically like their open chain analogs. The exceptions are for small ring compounds where angle strain may give rise to reactions that are not typical of other molecules. docsity.com Epoxides: CH2H2C O CHH2C O CH3 O O ethylene oxide propylene oxide cyclopentene oxide (oxirane) (methyloxirane) C6H5CO3H Synthesis: β-butylene oxide cis-2-butene docsity.com epoxides, reactions: 1) acid catalyzed addition CH2H2C O CH2H2C O CH2H2C O H2O, H + CH3CH2OH, H + HBr OH CH2CH2 OH OH CH3CH2-O-CH2CH2 OH CH2CH2 Br docsity.com mechanism for base-catalyzed addition to an epoxide: CC O C C Z OH 1) 2) + Z C C O ZRDS C C O Z + HZ + Z docsity.com acid catalyzed addition to unsymmetric epoxides? CH2CH O H3C CH2CH O H3C OH + H2O, H +  CH3CHCH2 OH which oxygen in the product came from the water? + H2 18O, H+  18OH CH3CHCH2 OH docsity.com CH2CH O H3C CH2CH O H3C CH3 O + CH3OH, H +  CH3CHCH2 OH Br + HBr  CH3CHCH2 OH docsity.com “variable transition state” Z acid: — C — C — OH δ+ δ+ ‡ base: Z — C — C — O δ- ‡ Bond breaking is occurring faster than bond making, making the carbon slightly positive. C δ+ : 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 docsity.com CH2CH O H3C CH2CH O H3C Acid: Base: Z + HZ  CH3CHCH2 OH Z + Z-, HZ  CH3CHCH2 OH Cδ+: Z to 2o carbon steric factors: Z to 1o carbon docsity.com