[PDF] [PDF] AMINES

[PDF] AMINES

The prefix N- (italicized) is added as a locant to identify substituents on the amino nitrogen as needed Page 8 IUPAC Nomenclature of Amines 8 (b) The 

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There are many naturally occurring organic compounds that The nomenclature for primary amines is similar to that of alcohols, practice problem 24 1 (p 908)

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[PDF] Nomenclature

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AMINES

1

Amines

Introduction

2

Aminesareorganicderivativesofammoniainwhichoneor

moreofthehydrogenatomsofammoniahavebeenreplacedby alkylorarylgroups. HNH H

Ammonia

RNH H

Amines

RNH R RNR R

Natural Amines

3 Aminesoccurwidelyinnatureinbiologicalsystems(inboththe plantandanimalkingdom).Smalleraminesarecharacterisedby theirfishyodours. Serotonin,aneurotransmitterfoundinthegastrointestinaltract, regulatesmoodandappetite(isresponsibleforthefeelingof havinghadeatenenough).

Classification of Amines

4 Aminesareclassifiedasprimary,secondaryortertiarybasedon thedegreeofsubstitutiononnitrogen(numberofalkyloraryl residuesattachedtothenitrogen). Notethedifferenceinclassificationofalcoholsandamines: Alcoholsareclassifiedbythenumberofalkylgroupsonthe- carbon,butamines(asiswithamides)areclassifiedbythe numberofalkylorarylgroupsattachedtothenitrogen.

IUPAC Nomenclature of Amines

5 IntheIUPACnomenclature,aliphaticaminesarenamedintwo waysdependingonthecomplexityoftheirstructure: (a)Simpleprimaryaminesarenamedbyappendingthesuffix aminetothenameofthealkylgroup(radical).Consequently, theyarenamedasalkylaminesorarylamines.

Underthisnomenclature,theaminogroupispresumedtobe

connectedtoC-1.

IUPAC Nomenclature of Amines

6

Examples

Symmetricalsecondaryandtertiaryaminesarenamedbyadding tothenameoftheradical,aprefix-or-respectively, andthesuffixamine.

IUPAC Nomenclature of Amines

7

Examples

Unsymmetricallysubstitutedsecondaryandtertiaryaminesare namedasN-substitutedderivativesofprimaryamines.The longestcarbonchainprovidestheparentnameandtheothersare consideredN-substituentsoftheparentchain.TheprefixN- (italicized)isaddedasalocanttoidentifysubstituentsonthe aminonitrogenasneeded.

IUPAC Nomenclature of Amines

8 (b)Thealternativesystemofnamingaliphaticaminesis analogoustothatofalcohols.Thenamesofaminesarederived byaddingthe-aminesuffixtothesystematicnameoftheparent alkane.Consequently,aminesarenamedasalkanamines. Theprocessbeginsbyidentifyingthelongestcarbonchainthat containstheaminogroupandthennumberingfromtheendof thechainthatgivestheaminogroupthelowestlocant.

NH2CH3CH2

Ethanamine

NH2CH3CH2CH2CH

CH3

2-Pentanamine

OHCH3CH2CH2CH

CH3

2-Pentanol

AlcoholAmine

OHCH3CH2

Ethanol

1 2 345

12HNCH3CH2

N-methylethanamine

HNCH3CHCH2CH

CH3

N-Cyclopropyl-4-methyl-2-Pentanamine

1 2 345
12 CH3 CH3

IUPAC Nomenclature of Amines

9 Aliphaticaminesinwhichtheaminogroupisattacheddirectly toaringarealsonamedinthesamewayascycloalkanamines. Thenumberinginsubstitutedsystembeginsfromthecarbon attachedtotheaminogroup.

IUPAC Nomenclature of Aromatic Amines

10 Aromaticaminesarenamedasderivativesofaniline.Substituted anilinesarenumberedbeginningatthecarbonthatbearsthe aminogroupandthedirectionofnumberingisgovernedbythe usualpointof.

IUPAC Nomenclature of Heterocyclic

Amines

11 Heterocyclicaminesarecycliccompoundsinwhichoneormore oftheatomsoftheringarenitrogenatoms.

IUPAC Nomenclature of Heterocyclic

Amines

12 Aromaticheterocyclicaminesalsoexist.Theheterocyclic nitrogenisalwaysnumberedasposition1

Examples

Properties of Amines

Physical Properties of Amines

13

Justlikealcohols,aminesarepolarcompounds.However,

becausenitrogenislesselectronegativethanoxygen,theN-H bondislesspolarthantheO-Hbondandhydrogenbonds betweenaminemoleculesareweakerthanthosebetweenalcohol molecules.

Thepolarnatureofaminesinfluencesmanyofitsphysical

propertiessuchasboilingpoint.Forsimilarlyconstituted compounds,alkylamineshaveboilingpointswhicharehigher thanthoseofalkanes,butlowerthanthoseofalcohols.

Examples

CH3CH2CH3CH3CH2NH2CH3CH2OH

PropaneEthylamineEthanol

Boiling Point-42 oC17 oC78 oC

Physical Properties of Amines

14 PrimaryandsecondaryamineshaveN-Hbonds,allowingthem toformintermolecularhydrogenbonds.Becauseprimaryamines havetwoN-Hbonds,hydrogenbondingismoresignificantin primaryaminesthaninsecondaryamines.HavingnoN-H bonds,puretertiaryaminescannotengage/participatein hydrogenbondingbetweentheirownmolecules.Sincehydrogen bondingsignificantlyaffectstheboilingpointofcompounds,it isnotsurprisingthatamongisomericamines,primaryamines havethehighestboilingpointsandtertiaryaminesthelowest.

Examples

(CH3)3NCH3CH2CH2NH2CH3CH2NHCH3

TriethylaminePropylamineN-Methylethylamine

Boiling Point3 oC50 oC34 oC

(Primary amine)(Secondary amine)(Tertiary amine)

Basicityof Amines

15 Theunsharedpairofelectronsonthenitrogenatomofanamine dominatesthechemistryofaminesandisresponsibleforthe basicity(sharingtheirlonepairofelectronswithaproton)and nucleophilicity(sharingtheirlonepairwithanelectrophilic carbon). Althoughaminesareweakbases,theyareconsiderablymore basicthanalcohols,ethers,andwater.Indeedasaclassof organiccompounds,aminesarethestrongestbasesofallneutral molecules.NHRH

Lone pair of electrons readily

available for bond formation

Basicityof Amines

16

Whenanamineisdissolvedinwater,anequilibriumis

establishedinwhichthewateractsasanacidandtransfersa protontotheamine.Aqueoussolutionsofaminesarebasic becauseofthefollowingequilibrium:

Basicityof Amines

17 ThebaseconstantKboritspKb(-logKb)can,therefore,beused tocomparetherelativebasicitiesofthevariousamines.Fromthe equation,itshouldbeclearthatgroups(electron-donating)that stabilizethepositivechargeonnitrogenenhancethebasicityof theamine.

Variation of BasicityAmong Alkylamines

18 Theelectronreleasefromalkylgroupsprovidestheprinciple mechanismbywhichtheconjugateacidoftheamineisstabilized inthegas-phase.Themorealkylgroupsattachedtothepositively chargednitrogen,themorestablethealkylammoniumion becomes. Thebasicityofalkylaminesinthegas-phaseincreasesinthe order: N H HHN R RR N H RHAmmonia (Least basic)

Primary amineSecondary amineTertiary amine

(Most basic)

Order of basicity in gas-phase

Basicityof Saturated Heterocyclic Amines

19 Saturatedheterocyclicaminesarejustasbasicasthetypical acyclicaminesthatcontainthesameheteroatom.Forexample, pyrrolidine,piperidineandmorpholinebehaveliketypical secondaryamines.N-Methylpyrrolidinebehaveslikeatypical tertiaryamine.

Basicityof Arylamines

20 Arylamines(pKb=10)suchasanilinearefarlessbasicthan alkylamines(pKb=4).Forexample,anilineislessbasicthan cyclohexylaminebynearlyamilliontimes.

Basicityof Arylamines

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