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StudentNotesSection14 - Section 14: Amines and Anilines 202...

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Section 14: Amines and Anilines 202 Section 14: Amines and Anilines 14.1 Introduction 14.1.1 Nomenclature Amines are organic analogues of ammonia in the same way that alcohols and ethers are organic analogues of water. Amines may be classified as being substituted with alkyl groups (alkylamines) or aromatic rings (arylamines). They may also be classified as primary, secondary or tertiary. In this case, these terms indicate the number of carbon atoms bonded to the nitrogen atom. Simple primary amines may be named as the alkylamine. More complex amine compounds are named for the parent alkane, substituting the –e suffix for – amine . Where the parent compound contains a group with higher priority (such as a carbonyl containing group), the amino - prefix is used. Symmetrical secondary and tertiary amines are named using di- and tri- prefixes. Unsymmetrical amines are named for the largest parent alkane, as above, with the N -alkyl prefix used to identify the group or groups attached to nitrogen. The N -alkyl substituents are listed alphabetically.
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Section 14: Amines and Anilines 203 There are common trivial names for the simplest arylamines NH 2 NH 2 CH 3 aniline o-toluidine (m- and p- isomers exist) There are a large number of heterocyclic amines, many of which have trivial names. In simple cases, the numbering begins at the N atom. N NH pyridine pyrrole N quinoline N isoquinoline N H indole Exceptions: piperidine pyrrolidine N H indoline N isoindoline 1 2 3 H 1 2 3 1 2 3 4 5 6 7 8 If there are two N atoms, the numbering proceeds such that the second N is at the lowest numbered position. Note that in the instance of imidazole, the cyclic N-H group outranks the cyclic N group. N N pyrimidine 1 2 3 N N H imidazole 1 2 3 N N pyridazine 1 2 NN pyrazine 3 N N N H N 1 2 4 9 8 7 5 6 Exception: purine Alkyl and aryl Phosphines (PR 3 ) and phosphonium salts (PR 4 + X - ) are named in a similar manner to the amines, as are the alkyl and aryl arsines (AsR 3 ).
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Section 14: Amines and Anilines 204 14.1.2 Structure and Properties The bonding of alkylamines is similar in many respects to the bonding in ammonia: the central nitrogen atom is sp 3 hybridized, due to the presence of a non-bonding electron pair – this is a pyramidal center. N R R' H N R R' H = N R H R' In principle, an amine with three different substituents (and the electron pair) on nitrogen may be considered to be chiral – we might expect such amines to display optical activity. In practice, such behavior is not observed – the amine is rapidly interconverted between the two chiral forms, leading to an overall racemate. N R R' H N R R' H N R R' H sp 3 sp 3 sp 2 The barrier to inversion is small for amines (approximately 25 kJ/mol). Even at very low temperatures, the inversion will still occur, as the barrier is low enough to allow significant quantum tunneling.
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This note was uploaded on 10/28/2010 for the course CHEM 235 taught by Professor Dr.poole during the Spring '10 term at Ball State.

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StudentNotesSection14 - Section 14: Amines and Anilines 202...

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