Examples of amide in the following topics:
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- As in the case of amines, amides are classified as 1º, 2º or 3º, depending on the number of alkyl groups bonded to the nitrogen.
- Most of the functions are amides or esters, cantharidin being a rare example of a natural anhydride.
- Cyclic esters are called lactones, and cyclic amides are referred to as lactams.
- Penicillin G has two amide functions, one of which is a β-lactam.
- The Greek letter locates the nitrogen relative to the carbonyl group of the amide.
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- Most base reagents are alkoxide salts, amines or amide salts.
- Since alcohols are much stronger acids than amines, their conjugate bases are weaker than amide bases, and fill the gap in base strength between amines and amide salts.
- Finally, the two amide bases see widespread use in generating enolate bases from carbonyl compounds and other weak carbon acids.
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- When electrophiles bond to an amide, they do so at the oxygen atom in preference to the nitrogen.
- One practical application of this behavior lies in the dehydration of 1º-amides to nitriles by treatment with thionyl chloride.
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- Similar hydrogen bonding occurs between molecules of 1º and 2º-amides (amides having at least one N–H bond), and the first three compounds in the table serve as hydrogen bonding examples.
- The relatively high boiling points of equivalent 3º-amides and nitriles are probably due to the high polarity of these functions.
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- The strongly deactivating sulfonic acid substituent is easily converted to a DMG by amide formation.
- The third diagram above shows the DoM of such an amide.
- Direct electrophilic substitution would normally occur at the meta position, so the action of the amide DMG is particularly noteworthy.
- A similar amide derivative of a carboxylic acid substituent may be used for DoM, as shown in the following diagram.
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- Amides: The name of the related acid is used first and the oic acid or ic acid suffix is replaced by amide (only for 1º-amides). e.g.
- CH3CONH2 is ethanamide (or acetamide). 2º & 3º-amides have alkyl substituents on the nitrogen atom.
- Cyclic amides are called lactams.
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- Reactivity: acyl halides > anhydrides >> esters ≈ acids >> amides
- An interesting exception to the low reactivity of amides is found in beta-lactams such as penicillin G.
- Although amines are among the most reactive nucleophiles, only 1º and 2º-amines give stable amide products.
- This explains why reactions #2 & 3 do not give amide products.
- No acylation reactions of amides were shown in these problems.
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- If the amine and carboxylic acid functional groups in amino acids join together to form amide bonds, a chain of amino acid units, called a peptide, is formed.
- This restriction is due to the rigid nature of the amide (peptide) bond.
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- Chloro and bromobenzene reacted with the very strong base sodium amide (NaNH2 at low temperature (-33 ºC in liquid ammonia) to give good yields of aniline (aminobenzene).
- The steric bulk of the methoxy group and the ability of its ether oxygen to stabilize an adjacent anion result in a substantial bias in the addition of amide anion or ammonia.
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- Nitrogen is more basic than oxygen, and amide anions are poorer leaving groups than alkoxide anions.
- In the case of the amide, aldehyde formation requires the loss of an aluminum amide (R'2N–Al), an unlikely process.
- This is the course followed by most amide reductions; but in the case of 1º-amides, the acidity of the nitrogen hydrogens coupled with the basicity of hydride enables a facile elimination of the oxygen (as an oxide moiety).
- Second, NaBH4 is much less reactive than LAH, failing to reduce amides and acids (they form carboxylate salts) at all, and reducing esters very slowly.
- This remains a primary application of this reagent, but it also effects rapid and complete reduction of carboxylic acids, amides and nitriles.