Download Amines are compounds characterized by the presence of

Amines are compounds characterized by the presence of a nitrogen
atom, a lone pair of electrons, and three substituents.
LEARNING OBJECTIVE [ edit ]
Identify the general properties of amines
KEY POINTS [ edit ]
Due to the lone pair of electrons, amines are basiccompounds. The basicity of the compound can
be influenced by neighboring atoms, steric bulk, and the solubility of the corresponding cation to
be formed.
Amine compounds can hydrogen bond, which affords them solubility in water and
elevated boiling points.
The general structure of an amine is a nitrogen atom with a lone pair of electrons and
three substituents. However, the nitrogen may bind to four substituents, leaving a positive charge
on the nitrogen atom. These charged species can serve as intermediates for important reactions.
TERMS [ edit ]
aliphatic
Of a class of organic compounds in which the carbon atoms are arranged in an open chain.
chiral
Literally, "handedness;" refers to a compound in which central atoms are bonded to multiple
different substituents, such that the mirror image of the compound is not identical to the original.
amine
Organic compounds or the functional group that contains a basic nitrogen atom with a lone pair.
inversion
For a secondary or tertiary amine bonded to three different substitutents, the flipping of the
three bonds about the central N atom, resulting in the opposite stereoisomer.
Give us feedback on this content: FULL TEXT [ edit ]
The amine functionalgroupcontains a
basic nitrogen atom with a lone pair of
electrons. As such, the group is derivative
of ammonia, in which one or more
hydrogen atoms have been replaced by a
carbon­containing substituent.
Compounds with the nitrogen group
attached to a carbonyl within the
structure are referred to asamides, and
they have the structure R­CO­NR'R".
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Amine groups bonded to an aromatic (conjugated cyclic) structure are known as aromatic
amines. The aromatic structure effectively decreases the alkalinity of the amine, while the
presence of the amine group significantly decreases thereactivity of the ring due to an
electron donating effect. Theprefix "amino­" or the suffix "­amine" is used when naming an
amine compound. An organic compound with multiple amino groups is called a diamine,
triamine, tetramine, etc.
Amine Structure
Amines are generally organized into categories based on their bonding environments.
Amines that have one of their three hydrogen atoms replaced by an alkyl or aromatic
substituent are referred to as primary amines. Secondary amines are those that have two
substituents and one hydrogen bonded to a nitrogen. Tertiary amines are amines whose
hydrogens have been completely replaced by organic substituents. Finally, cyclic amines are
those in which the nitrogen has been incorporated into a ring structure, effectively making it
either a secondary or tertiary amine. The general structure of an amine contains a nitrogen
atom, a lone pair of electrons, and three substituents. However, it is possible to have four
organic substituents on the nitrogen, making it an ammonium cation with a charged
nitrogen center.
Tertiary amine
The central carbon is attached to an amine group and three other carbon atoms.
Physical Properties of Amines
Amines are able to hydrogen bond. As a result, the boiling points of these compounds are
higher than those of the corresponding phosphines, but lower than those of the
corresponding alcohols, which hydrogen bond to a stronger extent. Amines also display some
solubility in water. However, the solubility decreases with an increase in carbon atoms, due
to the increased hydrophobicity of the compound as the chain length
increases. Aliphatic amines, which are amines connected to an alkyl chain, display solubility
in organic polar solvents. Aromatic amines, which are amines that participate in a
conjugated ring, donate their lone pair of electrons into the benzene ring, and thus their
ability to engage in hydrogen bonding decreases. This results in a decrease in their solubility
in water and high boiling points.
Acidity and Alkalinity of Amines
Amines of the type NHRR' and NR'R''R''' are chiral molecules and can undergo inversion.
Since the barrier for inversion is quite low (~7 kcal/mol), these compounds cannot be
resolved optically. Amines are bases, and their basicity depends on the electronic properties
of the substituents (alkyl groups enhance the basicity; aryl groups diminish it), steric
hindrance, and the degree of solvation of the protonated amine. In general, the effect of alkyl
groups raises the energyof the lone pair of electrons, thus elevating the basicity. Thus, the
basicity of an amine can be expected to increase with the number of alkyl groups on the
amine. Additionally, the effect of the aromatic ring delocalizes the lone pair of electrons on
nitrogen into the ring, resulting in decreased basicity. The solvation of protonated amines
changes upon their conversion to ammonium compounds. Typically, salts of ammonium
compounds exhibit the following order of solubility in water: primary ammonium (RNH3+) >
secondary ammonium (R2NH2+) > tertiary ammonium (R3NH+). Quaternary ammonium
salts usually exhibit the lowest solubility of the series.
Amine Preparation and Reactivity
Industrially, amines are prepared from ammonia by alkylation with alcohols. They can also
be prepared viareduction of nitriles to amines using hydrogen in the presence of a
nickel catalyst. Amines are quite reactive due to their basicity as well as their nucleophilicity.
Most primary amines are good ligands and react with metal ions to
yieldcoordination complexes. One of the most important reactions for amines is their
formation of imines, or organic compounds where nitrogen participates in a double bond,
upon reacting with ketones or aldehydes.
Imine formation
A primary amine is reacted with an aldehyde to produce an imine.
Applications of Amines
Amines are ubiquitous in biology. Many important molecules are amine­based, such as
neurotransmitters and amino acids. Their applications in the world include being starting
material for dyes and models for drug design. They are also used for gas treatment, such as
removing CO2 fromcombustion gases.