3 introduction to organic chemistry Alevel考试化学课件.pptx

Isomerism

Whatareisomers?Isomersaremoleculesthathavethesamemolecularformula,buthaveadifferentarrangementoftheatomsinspace.Thatexcludesanydifferentarrangementswhicharesimplyduetothemoleculerotatingasawhole,orrotatingaboutparticularbonds.

TypesofstructuralisomerismTypesofStereoisomerism

TypesofstructuralisomerismChainisomerismTheseisomersarisebecauseofthepossibilityofbranchingincarbonchains.Forexample,therearetwoisomersofbutane,C4H10.Inoneofthem,thecarbonatomslieinastraightchainwhereasintheotherthechainisbranched.

Pentane,C5H12,hasthreechainisomers.Ifyouthinkyoucanfindanyothers,theyaresimplytwistedversionsoftheonesbelow.Ifindoubtmakesomemodels.

PositionisomerismInpositionisomerism,thebasiccarbonskeletonremainsunchanged,butimportantgroupsaremovedaroundonthatskeleton.Forexample,therearetwostructuralisomerswiththemolecularformulaC3H7Br.Inoneofthemthebromineatomisontheendofthechain,whereasintheotheritsattachedinthemiddle.

AnothersimilarexampleoccursinalcoholssuchasC4H9OH

FunctionalgroupisomerismInthisvarietyofstructuralisomerism,theisomerscontaindifferentfunctionalgroups-thatis,theybelongtodifferentfamiliesofcompounds(differenthomologoussearies).Forexample,amolecularformulaC3H6Ocouldbeeitherpropanal(analdehyde)orpropanone(aketone).

AnothercommonexampleisillustratedbythemolecularformulaC3H6O2.Amongsttheseveralstructuralisomersofthisarepropanoicacid(acarboxylicacid)andmethylethanoate(anester).

Stereoisomerismareisomericmoleculesthathavethesamemolecularformulaandsequenceofbondedatoms(constitution),butwhichdifferonlyinthethree-dimensionalorientationsoftheiratomsinspace.Structuralisomerssharethesamemolecularformula,butthebondconnectionsand/ortheirorderbetweendifferentatoms/groupsdif