Carey-Chapter-3-Alkane-Conformations-Oglethorpe-University：卡蕾3章烷烃构象-奥格尔索普大学文教学课件

3.10

ConformationalAnalysisof

MonosubstitutedCyclohexanesmoststableconformationischairsubstituentismorestablewhenequatorialDr.Wolf'sCHM201&2021Methylcyclohexane5%95% Chairchairinterconversionoccurs,butatanyinstant95%ofthemoleculeshavetheirmethylgroupequatorial. Axialmethylgroupismorecrowdedthananequatorialone.CH3CH3Dr.Wolf'sCHM201&2022Methylcyclohexane5%95% Sourceofcrowdingiscloseapproachtoaxialhydrogensonsamesideofring. Crowdingiscalleda"1,3-diaxialrepulsion"andisatypeofvanderWaalsstrain.Dr.Wolf'sCHM201&2023Fluorocyclohexane40%60% Crowdingislesspronouncedwitha"small"substituentsuchasfluorine. Sizeofsubstituentisrelatedtoitsbranching.FFDr.Wolf'sCHM201&2024tert-ButylcyclohexaneLessthan0.01%Greaterthan99.99% Crowdingismorepronouncedwitha"bulky"substituentsuchastert-butyl.

tert-Butylishighlybranched.C(CH3)3C(CH3)3Dr.Wolf'sCHM201&2025tert-ButylcyclohexanevanderWaals

straindueto

1,3-diaxial

repulsionsDr.Wolf'sCHM201&20263.11

DisubstitutedCycloalkanes:

StereoisomersStereoisomersareisomersthathave

sameconstitutionbutdifferent

arrangementofatomsinspaceDr.Wolf'sCHM201&2027IsomersConstitutionalisomersStereoisomersDr.Wolf'sCHM201&20281,2-DimethylcyclopropaneTherearetwostereoisomersof

1,2-dimethylcyclopropane.Theydifferinspatialarrangementofatoms.Dr.Wolf'sCHM201&20291,2-Dimethylcyclopropanecis-1,2-Dimethylcyclopropanehasmethylgroups

onsamesideofring.trans-1,2-Dimethylcyclopropanehasmethylgroups

onoppositesides.Dr.Wolf'sCHM201&20210Relativestabilitiesofstereoisomersmaybe

determinedfromheatsofcombustion.Dr.Wolf'sCHM201&202113371kJ/mol3366kJ/molvanderWaalsstrainmakescis

stereoisomerlessstablethantransDr.Wolf'sCHM201&202123.12

ConformationalAnalysisof

DisubstitutedCyclohexanesDr.Wolf'sCHM201&202131,4-DimethylcyclohexanestereoisomerscistransCH35219kJ/mol5212kJ/mollessstablemorestableTransstereoisomerismorestablethancis,but

methylgroupsaretoofaraparttocrowdeachother.H3CHHH3CCH3HHDr.Wolf'sCHM201&20214Conformationalanalysisof

cis-1,4-dimethylcyclohexaneCH3

Twoequivalentconformations;eachhasoneaxial

methylgroupandoneequatorialmethylgroupH3CHHHCH3HCH3HH3CHCH3Dr.Wolf'sCHM201&20215Conformationalanalysisof

trans-1,4-dimethylcyclohexane

Twoconformationsarenotequivalent;moststable

conformationhasbothmethylgroupsequatorial.CH3H3CHHHH3CHCH3HH3CHCH3Dr.Wolf'sCHM201&202161,2-Dimethylcyclohexanestereoisomerscistrans5223kJ/mol5217kJ/mollessstablemorestableAnalogousto1,4inthattransismorestable

thancis.CH3CH3HHH3CCH3HHDr.Wolf'sCHM201&20217Conformationalanalysisof

cis-1,2-dimethylcyclohexaneTwoequivalentconformations;eachhasoneaxial

methylgroupandoneequatorialmethylgroupCH3CH3HH

HCH3HCH3HCH3HCH3Dr.Wolf'sCHM201&20218Conformationalanalysisof

trans-1,2-dimethylcyclohexane

Twoconformationsarenotequivalent;moststable

conformationhasbothmethylgroupsequatorial.CH3H3CHHHCH3HCH3HH3CHCH3Dr.Wolf'sCHM201&202191,3-Dimethylcyclohexanestereoisomerscistrans5212kJ/mol5219kJ/molmorestablelessstableUnlike1,2and1,4;cis-1,3ismorestablethantrans.H3CCH3HHCH3H3CHHDr.Wolf'sCHM201&20220Conformationalanalysisof

cis-1,3-dimethylcyclohexaneTwoconformationsarenotequivalent;moststable

conformationhasbothmethylgroupsequatorial.H3CHHCH3CH3H3CHH

HCH3HCH3Dr.Wolf'sCHM201&20221Conformationalanalysisof

trans-1,3-dimethylcyclohexane

Twoequivalentconformations;eachhasoneaxial

andoneequatorialmethylgroup.H3CHHCH3

HH3CHCH3H3CCH3HHDr.Wolf'sCHM201&20222Table3.2HeatsofCombustionof

IsomericDimethylcyclohexanesCompound Orientation -DH°cis-1,2-dimethyl ax-eq 5223

trans-1,2-dimethyl eq-eq 5217*cis-1,3-dimethyl eq-eq 5212*

trans-1,3-dimethyl ax-eq 5219cis-1,4-dimethyl ax-eq 5219

trans-1,4-dimethyl eq-eq 5212**morestablestereoisomerofpairDr.Wolf'sCHM201&202233.13

MediumandLargeRingsDr.Wolf'sCHM201&20224CycloheptaneandLargerRingsMorecomplicatedthancyclohexane.Commonforseveralconformationstobeof

similarenergy.Principlesarethesame,however.

Minimizetotalstrain.Dr.Wolf'sCHM201&202253.14

PolycyclicRingSystemsContainmorethanonering…..bicyclic,tricyclic,tetracyclic,etc.Dr.Wolf'sCHM201&20226Numberofringsequalsminimumnumberofbonddisconnections

requiredtogiveanoncyclicspeciesDr.Wolf'sCHM201&20227MonocyclicrequiresonebonddisconnectionDr.Wolf'sCHM201&20228BicyclicrequirestwobonddisconnectionsDr.Wolf'sCHM201&20229BicyclicrequirestwobonddisconnectionsDr.Wolf'sCHM201&20230TypesofringsystemsspirocyclicfusedringbridgedringDr.Wolf'sCHM201&20231SpirocycliconeatomcommontotworingsSpiro[4.5]decaneDr.Wolf'sCHM201&20232FusedringadjacentatomscommontotworingstworingsshareacommonsideBicyclo[4.3.0]nonaneDr.Wolf'sCHM201&20233BridgedringnonadjacentatomscommontotworingsBicyclo[3.2.1]octane

Dr.Wolf'sCHM201&20234SteroidscarbonskeletonistetracyclicDr.Wolf'sCHM201&202353.15

HeterocyclicCompounds