有機(jī)分子的結(jié)構(gòu)式The-Shapes-of-Some-Simple-Molecules課件

1.7

StructuralFormulasofOrganicMolecules1.7

StructuralFormulasofOrgConstitutionTheorderinwhichtheatomsofamoleculeareconnectediscalleditsconstitutionorconnectivity.TheconstitutionofamoleculemustbedeterminedinordertowriteaLewisstructure.ConstitutionTheorderinwhichStep1:

Themolecularformulaandtheconnectivityaredeterminedbyexperiment.Table1.4HowtoWriteLewisStructuresStep1:

ThemolecularformulStep1:

Themolecularformulaandtheconnectivityaredeterminedbyexperiment.Example:

MethylnitritehasthemolecularformulaCH3NO2.Allhydrogensarebondedtocarbon,andtheorderofatomicconnectionsisCONO.Table1.4HowtoWriteLewisStructuresStep1:

ThemolecularformulStep2:

Countthenumberofvalenceelectrons.Foraneutralmoleculethisisequaltothenumberofvalenceelectronsoftheconstituentatoms.Table1.4HowtoWriteLewisStructuresStep2:

CountthenumberofStep2:

Countthenumberofvalenceelectrons.Foraneutralmoleculethisisequaltothenumberofvalenceelectronsoftheconstituentatoms.Example(CH3NO2):

Eachhydrogencontributes1valenceelectron.Eachcarboncontributes4,nitrogen5,andeachoxygen6foratotalof24.Table1.4HowtoWriteLewisStructuresStep2:

CountthenumberofStep3:

Connecttheatomsbyacovalentbondrepresentedbyadash.Table1.4HowtoWriteLewisStructuresStep3:

ConnecttheatomsbyStep3:

Connecttheatomsbyacovalentbondrepresentedbyadash.Example:

Methylnitritehasthepartialstructure:Table1.4HowtoWriteLewisStructuresCONOHHHStep3:

ConnecttheatomsbyStep4:

Subtractthenumberofelectronsinbondsfromthetotalnumberofvalenceelectrons.Table1.4HowtoWriteLewisStructuresCONOHHHStep4:

SubtractthenumberStep4:

Subtractthenumberofelectronsinbondsfromthetotalnumberofvalenceelectrons.Example:

24valenceelectrons–12electronsinbonds.Therefore,12moreelectronstoassign.Table1.4HowtoWriteLewisStructuresStep4:

SubtractthenumberStep5:

Addelectronsinpairssothatasmanyatomsaspossiblehave8electrons.Startwiththemostelectronegativeatom.

Table1.4HowtoWriteLewisStructuresStep5:

AddelectronsinpaiStep5:

Addelectronsinpairssothatasmanyatomsaspossiblehave8electrons.Startwiththemostelectronegativeatom.Example:

Theremaining12electronsinmethylnitriteareaddedas6pairs.Table1.4HowtoWriteLewisStructures..CONOHHH....:....Step5:

AddelectronsinpaiStep6:

Ifanatomlacksanoctet,useelectronpairsonanadjacentatomtoformadoubleortriplebond.Example:

Nitrogenhasonly6electronsinthestructureshown.Table1.4HowtoWriteLewisStructures..CONOHHH....:....Step6:

IfanatomlacksanStep6:

Ifanatomlacksanoctet,useelectronpairsonanadjacentatomtoformadoubleortriplebond.Example:

AlltheatomshaveoctetsinthisLewisstructure.Table1.4HowtoWriteLewisStructures....CONOHHH..:..Step6:

IfanatomlacksanStep7:

Calculateformalcharges.

Example:

NoneoftheatomspossessaformalchargeinthisLewisstructure.Table1.4HowtoWriteLewisStructures....CONOHHH..:..Step7:

CalculateformalchaStep7:

Calculateformalcharges.

Example:

Thisstructurehasformalcharges;islessstableLewisstructure.Table1.4HowtoWriteLewisStructures....CONOHHH..:..+–Step7:

CalculateformalchaCondensedstructuralformulasLewisstructuresinwhichmany(orall)covalentbondsandelectronpairsareomitted.HOCCCHHHHHH::Hcanbecondensedto:CH3CHCH3OH(CH3)2CHOHorCondensedstructuralformulasLBond-lineformulasOmitatomsymbols.Representstructurebyshowingbondsbetweencarbonsandatomsotherthanhydrogen.Atomsotherthancarbonandhydrogenarecalledheteroatoms.CH3CH2CH2CH3isshownasCH3CH2CH2CH2OH

isshownasOHBond-lineformulasOmitatomsyBond-lineformulasOmitatomsymbols.Representstructurebyshowingbondsbetweencarbonsandatomsotherthanhydrogen.Atomsotherthancarbonandhydrogenarecalledheteroatoms.HClCCH2CH2CCH2CH2HHisshownasClBond-lineformulasOmitatomsy1.8

ConstitutionalIsomers1.8

ConstitutionalIsomersConstitutionalisomers Isomersaredifferentcompoundsthathavethesamemolecularformula.

Constitutionalisomersareisomersthatdifferintheorderinwhichtheatomsareconnected.

Anoldertermforconstitutionalisomersis“structuralisomers.”Constitutionalisomers IsomersAHistoricalNote In1823FriedrichW?hlerdiscoveredthatwhenammoniumcyanatewasdissolvedinhotwater,itwasconvertedtourea.

AmmoniumcyanateandureaareconstitutionalisomersofCH4N2O. Ammoniumcyanateis“inorganic.”Ureais“organic.”W?hleriscreditedwithanimportantearlycontributionthathelpedoverturnthetheoryof“vitalism.”NH4OCNAmmoniumcyanateH2NCNH2OUreaAHistoricalNote In1823FrieNitromethaneMethylnitrite..:HCOON::..–+HHExamplesofconstitutionalisomersBothhavethemolecularformulaCH3NO2buttheatomsareconnectedinadifferentorder...CONOHHH..:....NitromethaneMethylnitrite..:H1.9

Resonance1.9

ResonancetwoormoreLewisstructuresmaybe

writtenforcertaincompounds(orions)ResonancetwoormoreLewisstructuresmStep6:

Ifanatomlacksanoctet,useelectronpairsonanadjacentatomtoformadoubleortriplebond.Example:

Nitrogenhasonly6electronsinthestructureshown.Table1.4HowtoWriteLewisStructures..CONOHHH....:....Step6:

IfanatomlacksanStep6:

Ifanatomlacksanoctet,useelectronpairsonanadjacentatomtoformadoubleortriplebond.Example:

AlltheatomshaveoctetsinthisLewisstructure.Table1.4HowtoWriteLewisStructures....CONOHHH..:..Step6:

IfanatomlacksanStep7:

Calculateformalcharges.

Example:

NoneoftheatomspossessaformalchargeinthisLewisstructure.Table1.4HowtoWriteLewisStructures....CONOHHH..:..Step7:

CalculateformalchaStep7:

Calculateformalcharges.

Example:

Thisstructurehasformalcharges;islessstableLewisstructure.Table1.4HowtoWriteLewisStructures....CONOHHH..:..+–Step7:

Calculateformalchasameatomicpositionsdifferinelectronpositionsmorestable

Lewis

structurelessstable

Lewis

structure....CONOHHH..:..+–....CONOHHH..:..ResonanceStructuresofMethylNitritesameatomicpositionsmorestabsameatomicpositionsdifferinelectronpositionsmorestable

Lewis

structurelessstable

Lewis

structure....CONOHHH..:..+–....CONOHHH..:..ResonanceStructuresofMethylNitritesameatomicpositionsmorestab Electronsinmoleculesareoftendel