Amines (N-R3)
Amines
are classified (primary, secondary, tertiary) according to the number (one,
two, three) of alkyl groups attached to the central nitrogen atom. Amines can also be classified as symmetrical or asymmetrical, depending on whether the alkyl groups match or not. The functional group is called an amino group.
When
organisms decompose, protein breaks down into amines (putrescine (H2N(CH2)4NH2)
and cadaverine (H2N(CH2)5NH2)),
which have unpleasant odours.
Naming Amines
Amines
can be named as an alkyl derivative of ammonia (names listed alphabetically).
There is a second IUPAC-accepted naming method as well.
When naming, indicate the alkyl substituents in alphabetical order, separated by spaces and then add "amine."
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| We will only be looking at the first name for each compound. The second name is also accepted but we got 99 problems and another naming system ain't one of them. First compound: The carbon chain has five carbons (pentyl), attached to the amino group (amine). Second compound: Both carbon chains have two carbons (diethyl), attached to the amino group (amine). Third compound: One carbon chain has four carbons (butyl) and the other has two carbons (ethyl), attached to the amino group (amine). Fourth compound: All three carbon chains have two carbons (triethyl), attached to the amino group (amine). Fifth compound: Two carbon chains have two carbons (diethyl) and the other chain has three carbons (propyl), attached to the amino group (amine). Sixth compound: One carbon chain has two carbons (ethyl), another has five carbons (pentyl) and the other has three carbons (propyl), attached to the amino group (amine). |
Properties of Amines
The properties
of the amines are the results of the characteristics of the amino group:
─NH2
- polar and most can hydrogen bond (primary and secondary amines can H-bond, tertiary amines cannot)
- as the number of alkyl groups around the N increases, the intermolecular forces also increase (ammonia bp -33°C, methylamine -6°C, dimethylamine 8°C, trimethylamine 3°C)
- since the N-H bond is not a polar as the –OH bond, amines have lower bp than the analogous alcohols
Preparing Amines - Alkylation Reaction
Amines
are prepared by the reaction of ammonia (a weak base) with an alkyl
halide. The primary amine formed can
also react with an alkyl halide. The
secondary amine formed can also react with an alkyl halide. T he final product is a mix of
primary, secondary and tertiary amines, which can be separated using fractional
distillation, due to difference in bp.
 |
| In each case, the halogen atom pops off the alkyl halide and a hydrogen detaches from the nitrogen. Then, the nitrogen bonds to the carbon that used to hold the halogen atom. |
Amides (R-NH-CO-R)
The
amide linkage is very important in biology – it forms the backbone of protein
molecules. In proteins, the amide
linkages are called peptide bonds.
Naming Amides
The
nitrogen in the amide functional group may have zero, one or two alkyl groups
attached. If there is more than one
group on the N, order the names alphabetically. Similar to ester nomenclature, we always name the single bonded nitrogen side first (N- _____yl) and the double bonded oxygen side second (_____amide). Always number outward from the amide functional group.
 |
| First compound: The nitrogen side has no substituent ( ) and the oxygen side has four carbons (but), singly bonded (an) and the functional group (amide). Second compound: The nitrogen side has a three carbon chain (N-propyl) and the oxygen side has four carbons (but), singly bonded (an) and the functional group (amide) Third compound: The nitrogen side has a two carbon chain (N-ethyl) and a three carbon chain (N-propyl) and the oxygen side has four carbons (but), singly bonded (an) and the functional group (amide). Fourth compound: The nitrogen side has two carbon chains, each with two carbons (N,N-diethyl) and the oxygen side has four carbons (but), singly bonded (an) and the functional group (amide). |
Amides
are formed by the reaction of a carboxylic acid with ammonia or
primary/secondary amines (organic bases) in a condensation reaction.
 |
| !!TYPO ALERT!! The conditions for this reaction would be "sulfuric acid & heat", not "acid or base". The preparation of an amide is similar to an esterification reaction. The carboxylic acid loses its hydroxyl group and the amine loses one of the hydrogens on the amino group. These two pieces join together to form water. The carbon, of the carbonyl group, and the nitrogen of the amino group link to form an amide. NameIts! Name all the organic compounds in this reaction. The answer is at the end of the lesson. |
The properties
of the amides are the results of the characteristics of the amide group:
O H
║ ｜
─C─N─
- carbonyl group is polar; amino group is polar and can H-bond
- mp, bp and water solubility is quite high
- amides are weak bases
- amides with an –NH2 group have higher mp and bp than amides with attached alkyl groups due to the increased H bond ability
Reactions of Amides – Hydrolysis Reaction
Like
esters, amides can be hydrolyzed in acidic or basic conditions to produce a
carb acid and an amine. This hydrolysis
occurs more slowly than that of an ester.
 |
| This reaction is the opposite of the condensation reaction above. The amide splits at the bond between the carbonyl carbon and the nitrogen. The carbonyl carbon picks up the OH from the water and the nitrogen picks up the H, producing an amine and an alcohol, respectively. NameIts! Name all the organic compounds in this reaction. The answer is at the end of the lesson. |
NameIts! Answers:
pentan-1-ol, 1-methylpropylamine, N-1-methylpropyl pentanamide
N-butyl 3,4-dimethylhexanamide, 3,4-dimethylhexanoic acid, butylamine
Homework # 63-75
Success Criteria
- general formula - be able to provide the general formula, draw the functional group and name the functional group (when possible) for each family (alkanes, alkenes, alkynes, cyclohydrocarbons, aromatics, alkyl halides, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines, amides)
- nomenclature - be able to draw a structure from a name or provide a name for a structure for all families
- properties for each family - be able to list, explain and use the properties to indicate highest (or lowest) mp, bp, water solubility, etc within a group of molecules
- reaction chemistry - be familiar with the name, reactants, products and conditions for all reactions (substitution (halogenation, etc), addition (halogenation, etc), condensation, hydrolysis, estrification, etc)
- polymers - addition and condensation polymers - be familiar with monomers vs polymers and the general properties for both; given reactants, predict products and vice versa; be able to write out a full reaction equation
