Amide
n
chemistry, an
amide is one of two kinds of compounds:
- the
organic functional group characterized by a
carbonyl group linked to a
nitrogen atom , or a compound that contains this
functional group ; or
- a particular kind of
nitrogen anion.
Many chemists make a pronunciation distinction between the two, saying
In the first sense referred to above, an amide is an
amine where one of the
nitrogen substituents is an acyl group; it is generally represented by the formula: R1
NR2R3 , where either or both R2 and R3 may be
hydrogen.
Encyclopedia
In
chemistry, an
amide is one of two kinds of compounds:
- the
organic functional group characterized by a
carbonyl group linked to a
nitrogen atom , or a compound that contains this
functional group ; or
- a particular kind of
nitrogen anion.
Many chemists make a pronunciation distinction between the two, saying
In the first sense referred to above, an amide is an
amine where one of the
nitrogen substituents is an acyl group; it is generally represented by the formula: R
1NR
2R
3 , where either or both R
2 and R
3 may be
hydrogen. Specifically, an amide can also be regarded as a derivative of a
carboxylic acid in which the hydroxyl group has been replaced by an
amine or
ammonia.
Compounds in which a
hydrogen atom on
nitrogen from
ammonia or an
amine is replaced by a
metal cation are also known as amides or
azanides.
The second sense of the word
amide is the amide anion, which is a deprotonated form of
ammonia or an
amine. It is generally represented by the formula: [R
1NR
2]
-, and is an extremely strong base, due to the extreme weakness of
ammonia and its analogues as Brønsted acids.
The remainder of this article is about the
carbonyl-
nitrogen sense of
amide. For examples of the anionic amide, see the articles
Sodium amide and
Lithium diisopropylamide.
Amide synthesis
In chemistry [i], a
solution is a homogeneous mixture [i] composed of one or more substances, known a ...
at neutral
pH. Amide formation plays a role in the synthesis of some
condensation polymers, such as
nylon and
Kevlar.
[i]
[i]
...
s.
Amide reactions
Amide properties
An amide linkage is kinetically stable to
hydrolysis. However, it can be hydrolysed in boiling alkali, as well as in strong acidic conditions. Amide linkages in a
biochemical context are called
peptide linkages. Amide linkages constitute a defining molecular feature of
proteins, the
secondary structure of which is due in part to the
hydrogen bonding abilities of amides.
Compared to
amines, amides are very weak bases. While the conjugate acid of an
amine has a pKa of about 9.5, the conjugate acid of an amide has a pKa around -0.5. Therefore amides don't have as clearly noticeable acid-base properties in
water. This lack of basicity is discussed in the
peptide bond article, and explained by the
electron-withdrawing nature of the
carbonyl group where the lone pair of
electrons on the
nitrogen is delocalized by resonance, thus forming a partial
double bond with the
carbonyl carbon and putting a negative charge on the
oxygen. On the other hand, amides are much stronger bases than
carboxylic acids,
esters,
aldehydes, and
ketones .
Derivatives
Sulfonamides are analogues of amides in which the atom double-bonded to
oxygen is
sulfur rather than
carbon.
Naming conventions
External links
