21 Amides and Imides
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D
erivatives o f carboxylie acids i n which the O H portion o f the C O O H group has been replaced b y N H (as such or substituted) are called amides or, more accurately, carboxamides. Such compounds have the generic structures RCONH , R C O N H R ' , and R C O N R ' R " , as well as R C O N H C O R , " and R C O N ( C O R ' ) C O R " . The latter two classes may be referred to as secondary amides and tertiary amides, respectively. Compounds containing the group —CONHCO— or —CON(R)CO— as part of a ring are called imides or, more accurately, carboximides. Broadly speaking, the class terms amide and imide also denote the corresponding nitrogen derivatives o f noncarboxylic acids such as those discussed in Chapters 18, 36, and 40—e.g., sulfonamides and amides o f phosphorus acids, as well as ionic derivatives o f ammonia such as sodium amide ( N a N H ). Sulfur analogs o f carboxamides and dicarboximides, called thioamides and thioimides, are included in this chapter. Naming o f peptides, a special subclass made up o f amides derived from α-amino carboxylic acids, is discussed in Chapter 30. 2
2
2
Recommended Nomenclature Practice Compounds o f the type R C O N H are preferably named by changing the ending oic acid i n the corresponding systematic alkanoic or alkanedioic acid name to amide, or the ending carboxylie acid, where that is used in the acid name, to carboxamide. 2
CH
3
CH CH CH CHCONH 3
2
2
2-Methylpentanamide 2
Cyclohexanecarboxamide
H NCOCH CH CH CH CONH 2
2
2
2
2
2
Hexanediamide 166
In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
21.
Amides and Imides
H 2 N
N
167 C O N H 2
^ ^CHCH CH CH^ CONH 2
2
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Compounds of the types R C O N H R ' and R C O N R ' R " are named as JV-substituted amides, excepting when the nitrogen atom is part of a ring; in that case they are named as substituted heterocyclic compounds.
CH3 CH3
J J CH CH CH CHCONCH=CH 3
2
2
COCHnCH
I
===
iV-Ethenyl-iV,2-dimethylpentanamide 2
CH^
O -N.
l-( 3-Butenoyl)azacyclopenta-2,4-diene
Likewise, compounds of the types ( R C O ) N H a n d ( R C O ) N , whether all R groups are alike or different, are best treated as N-substituted amides. For unsymmetrical structures the largest or most complex acyl group is preferably expressed in the parent name.. 2
CH CH CONHCOCH CH 3
/ \
2
2
3
N-Propanoylpropanamide
3
\—CON(COC= CCH ) / 3
2
N,N-Di-2-butynoylcyclohexanecarboxamide
Amides in which the —CONH— group is part of a ring, often called lactams, are best named as heterocyclic compounds—i.e., as ketones.
H Azacyclohexan-2-one
In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.
168
NOMENCLATURE OF ORGANIC COMPOUNDS
Similar treatment is generally to be preferred for imides, although systematic names expressing the imide function as a suffix may be formed by replacing the edioic acid ending o f the corresponding dibasic acid name with imide or b y changing the ending dicarboxylic acid to dicarboximide. H
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Azacyclohexane-2,6-dione Pentanimide
2-Azabenz [f] indan-1,3-dione 2,3-Naphthalenedicarboximide
Thioamides are named analogously to amides b y using the suffixes thioamide and carbothioamide (see Examples 15-18 in Table 21.1). Thioimides should be named as heterocyclic compounds (see Example 19). When the amide or imide function must be named as a substituting group, one o f two types o f prefix names is usually applicable. If attachment is through the carbon atom(s), the prefixes carbamoyl for H N C O — and iminodicarbonyl for —CONHCO— are used; if attachment is through the nitrogen atom, the prefix name is formed b y changing the final e o f the amide or imide name to o although for imide groups heterocyclic names are to be preferred. 2
Methyl 4-carbamoylcyclohexanecarboxylate
H NCO 2
CH =CHCH CONHCH CH COOH 2
2
2
2
3-(3-Butenamido)propanoic acid
2-( 1,3-Dioxo-2-azaindan-2-yl)ethanesulfonic acid 2-( 1,2-Benzenedicarboximido)ethanesulfonic acid
Alternatively, substituting groups of the types ( R C O ) N — and RCON
