AMIDE
While an ester can be thought of as a combination of a carboxylic acid and an
alcohol, an amide is the combination of a carboxylic acid and an amine. Amides have
the functional group:
O
|| |
-C-NAmides are classified as primary, secondary or tertiary depending upon how many
carbons bond to the N. If there is one carbon, it is primary; if there are two,
secondary and if there are three, tertiary. In this course we will name primary
amides only.
NAMING OF AMIDES
1) Locate the carbonyl group and name the parent carboxylic acid.
2) Replace the “oic acid” with the ending –amide.
3) A - Primary Amide – if there are two hydrogen atoms bonded to the nitrogen.
B – Secondary Amide – if there is one alkyl group attached to the nitrogen. Name and locate the alkyl group,
use the letter N to indicate that it is bonded to the nitrogen atom.
C – Tertiary Amide – if there are two alkyl groups attached to the nitrogen. Name and locate each alkyl group
alphabetically, use the letter N to locate before each group.
Eg.
O
||
CH3-CH-C-NH2
|
CH3
2-methylpropanamide
O
||
CH3-CH2-CH2-C-NH-CH2-CH3
N-ethylbutanamide
O
||
CH3-C-N-CH3
\
CH2-CH3
N-ethyl-N-methylethanamide
EXERCISE
1. Name and/or classify the following amides.
a)
O
b)
O
||
||
CH3-CH2-CH-CH2-C-NH2 CH3-CH-CH-C-NH2
|
| |
CH2-CH3
CH3 CH3
c)
O
||
CH3 –CH2-C-N-CH2-CH2-CH3
\
CH2-CH2-CH3
2. Give the condensed structural formulas for the following primary amides.
a) 2,2 - diethylpentanamide
b) 3,4-dibromobutanamide
c) hexanamide
PROPERTIES OF AMIDES
Because the N atom is an electron withdrawing group, the C-N and H-N
bonds are polar. As a result the physical properties of amides are similar to
carboxylic acids.
1) Primary amides have two N-H bonds (and because there are many electron pairs
on the molecule) and have even stronger hydrogen bonding than a carboxylic
acid. Secondary amides also have one N-H bond and experience hydrogen
bonding. Tertiary amides do not have an N-H bond and do not experience
hydrogen bonding.
2) Amides are water soluble with a low number of carbons. The longer the alkyl
groups in the molecule, the lower the solubility in water.
3) Primary amides have higher melting points and boiling points than carboxylic
acids. Many simple amides are solids at room temperature.
REACTIONS
Amides form from a reaction that is similar to an esterification. Instead of an
alcohol an amine is used with a carboxylic acid and one molecule of water is created.
The –OH group from the carboxylic acid and the -H from the –NH2 group will form
a water molecule.
O
||
CH3-CH2-C-OH + NH2-CH2-CH3 --->
O
||
CH3-CH2-C-NH-CH2-CH3
propanoic acid
N – ethylpropanamide
aminoethane
+
H2O
water