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Amines are organic compounds in which one or more H in ammonia, NH3, is replaced with alkyl or aromatic groups.
H H H| | |
H—N—H CH3—N—H CH3—N—CH3
ammonia
Amines
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Classification of AminesAmines are classified as primary, secondary, or tertiary.In a primary (1°) amine, one carbon group is bonded to the nitrogen atom.A secondary (2°) amine has two carbon groups.A tertiary (3°) amine has three carbon groups.
H CH3 CH3| | |
CH3—N—H CH3—N—H CH3—N—CH3
1° 2° 3°
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Models of Amines
The three-dimensional models show the shapes of amine molecules with one or more alkyl groups bonded to the nitrogen atom.
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Simple amines are named as alkylamines.The alkyl groups bonded to the N atom are listed in alphabetical order in front of amine.CH3—CH2—NH2 CH3—NH—CH3Ethylamine Dimethylamine
CH3|
CH3—N—CH2—CH3 Ethyldimethylamine
Common Names of Amines
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In the IUPAC system, amines are named as alkanamines. The –e in the alkane name of the longest chain is changed to –amine.The chain is numbered to locate the amine group and substituents.
NH2|
CH3—CH2—NH2 CH3—CH—CH3Ethanamine 2-Propanamine
IUPAC Names of Amines
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Each alkyl groups bonded to the N atom is named as N-alkyl groups in front of the amine name for the longest chain.
HN—CH3|
CH3—CH2—CH2—NH—CH3 CH3—CH—CH2—CH3
N-Methyl-1-propanamine N-Methyl-2-butanamine
Naming Secondary and Tertiary Amines
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Give the common and IUPAC names and classify as primary, secondary, or tertiary:A. CH3—CH2—CH2—NH2
CH3|
B. CH3—CH2—N—CH3
Learning Check
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A. CH3—CH2—CH2—NH2
1-propylamine, 1-propanamine, 1°
CH3|
B. CH3—CH2—N—CH3
ethyldimethylamine, N,N-dimethylethanamine, 3°
Solution
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Aromatic Amines
The amine of benzene is named aniline.
Aniline 3-Chloroaniline N-Methylaniline
NH CH3 NH2
Cl
NH2
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Boiling Points of Amines, Alcohols, and Alkanes
The boiling points of amines are higher than alkanes, but lower than alcohols of similar mass.
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Boiling points of some common amines are shown Boiling points of some common amines are shown in the Table 15.1in the Table 15.1
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Hydrogen Bonding for AminesThe polar N-H bond provides hydrogen bonding in 1°and 2° amines, but not 3°.However, the N-H bonds in amines are not as polar as the O-H bonds in alcohols.
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Solubility in WaterAmines with 1-5 carbon atoms are soluble in water.The N atom in amines forms hydrogen bonds with the polar O-H bond in water.
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Learning Check
Consider the following compounds:1) CH3—CH2—CH2—NH2
2) CH3—CH2—NH—CH3
3) CH3—CH2—CH2—CH3
A. Which compound has the highest boiling point?B. Which compound is soluble in water?
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SolutionConsider the following compounds:1) CH3—CH2—CH2—NH22) CH3—CH2—NH—CH33) CH3—CH2—CH2—CH3A. Which compound has the highest boiling point?1) CH3—CH2—CH2—NH2B. Which compound is soluble in water?1) CH3—CH2—CH2—NH22) CH3—CH2—NH—CH3
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Like ammonia, amines are weak bases in water.NH3 + H2O NH4
+ + OH–
ammonium hydroxide
CH3—NH2 + H2O CH3—NH3+ + OH–
methylammoniumhydroxide
15.4 Basicity of Amines
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An amine salt: Forms when an amine is neutralized by acid. Is named by replacing the amine part of the name with ammonium followed by the name of the negative ion.
CH3—NH2 + HCl CH3—NH3+ Cl–
Methylamine methylammonium chloride
15.5 Amine Salts
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Properties of Amine Salts Amine salts are:
Solids at room temperature.Soluble in water and body fluids.The form used for drugs.
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CocaineCocaine is sold illegally as an amine salt.Cocaine is reacted with NaOH to produce the free amine form known as “crack.”
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Heterocyclic AminesIn a heterocyclic amine, a five- or six-atom ring contains one or more nitrogen atoms.
N
NN
N
N
H
N
H
N
H
Pyrrolidine Pyrrole
Piperidine Pyridine Pyrimidine
N
N
N
N
H
Purine
N
HImidazole
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Alkaloids are:Physiologically active nitrogen-containing compounds.Produced by plants.Used as stimulants, anesthetics, and antidepressants.Often habit forming.
Alkaloids
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Caffeine:Is a stimulant of the central nervous system. Is found in coffee beans, tea, chocolate, and soft drinks.Contains an imidazolering.
Caffeine
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NicotineNicotine:
Increases the adrenaline level in the blood.Causes addiction to tobacco.Contains a pyrrolidine ring.
N
CH3
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Alkaloids Related to MorphineAlkaloids such as morphine and codeine are produced by the poppy.For centuries, morphine and codeine have been used as painkillers.Heroin is a modification of morphine.
Methadone
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PharmacologyAn area of research in pharmacology is to design drugs with some of the characteristics of alkaloids. The structures of cocaine and morphine are modified to produce anesthesia, but without the addictive side effects.
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PharmacologyParts of the morphine structure that produce anesthesia are found in procaine, lidocaine, and demerol.
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