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Preparing Your ACS Examination Organic Chemistry1 12

Preparing Your ACS Examination Organic Chemistry1 12 -...

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Unformatted text preview: Nomenclature NM-G. What is the IUPAC name for this compound? (A) methyl butanoate (C) propyl methanoate Knowledge Required: Procedure for naming esters. Thinking it Through.- Bsters are derivatives of carbonylic acids and alcohols. To name an ester, identify the alkyl group that is in the “alcohol" portion of the molecule and name it, then idenfify and name the “acid” part : the molecule.Theesterisnamedwiththealkylpartfirshandtheacidpmtisnamedasacarboxylate. For example. theesmafbenzoicacidandmethanolwouldbenamedasmethylbenzoate. 9 9 R-C-OH + H-O-R‘ -—- R—C—O—R' +H20 . "acid "alcohol pan" PM" In the probln . the alcohol portion is derived from 1-propanol. Tha'efore, the alkyl group is a wopyl group. The carboxyfic acid portion of the molecule is derived from ethanoic acid. Thus the answer is propyl ethanoate. which is (D). A helpful hint: Use "carbon atom counts" to eliminate choices which do not correspond to that of the given strucutre. For example. the ester CH3CHQCH2COOCHQCH3 contains a total of six carbon atoms. Therefore any suggestednamewhosccomponents wouldcontainotherthansixcarbonatomsmnstbemngandthatchoicecan beeliminated. lfthename“propyl edranoate“ wereapossible answer. itcouldherejected immediately hecausethe propyl yormoontainsflireecarbonatomsandethanoatecontaim twocarhonatoms.foratota.loffive.Similarly, ifthequestionaskedwhichoffmusnucnu'escorrespond withagiven name.itshouldhepossibletocountupthc number of carbon atoms suggested in the name and reject any possible structures that differ from this number. This approach will often narrow the choices, but it is usually necessary to examine the alkyl and acid portions of the ester closely to be absolutely sure. Using this “carbon atoms counts” approach. choice (B) can be rejected because methyl wopanoate is derived from methanol (1 carbonatom) andpropanoic acid (3 carbon atoms). The molecule shown inthequestion has five carbon atoms, so choice (B) can be eliminated from consideration. Similarly, choice (C) is eliminated because the namedescrihesanestuderivedfiomaB—catbon—atomalcoholandal-earbonammcarhoxylicacidIftwoormore choices havethecorrect number ofcarbonatoms. then look atthe sn'ucnnesofthealeohol's alkyl groupandatthe carboxylicacidportiontodetemtinewhichchoiceisconecLForexarnple.choice(A)cannotbethecorrectanswer becausentethylbutanoatewouldhaveamethylgroupasthealcoholpanoftheesterandbederivedfi'ombutanoic acid.Aglanceatthegivenmolecnleshowsthatitisnotdaivedfi-ombuunoicacid. sothischoicemustbe incorrect. ...
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