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Chapter 18
Amines and
Neurotransmitters
Based on Material Prepared by
Andrea D. Leonard
University of Louisiana at Lafayette
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Structure and Bonding
Amines are organic nitrogen compounds, which
are classified by the number of alkyl groups
bonded to the N atom.
A primary (1o) amine
has 1 C—N bond,
and has the general
structure RNH2.
A secondary (2o) amine
has 2 C—N bonds, and
has the general
structure R2NH.
A tertiary (3o) amine
has 3 C—N bond,
and has the general
structure R3N.
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Structure and Bonding
The 1o, 2o, and 3o amine N atom has a lone pair of
e−, which is omitted in condensed structures.
There are quarternary (4o) amines, but they do
not have a lone pair and bears a positive charge.
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Structure and Bonding
The amine N has a trigonal pyramidal shape,
with bond angles of ~109.5o.
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Nomenclature
A. Primary Amines
1o amines are named with either systematic or
common names.
To find the systematic name:
•find the longest carbon chain bonded to the
amine N atom
•change the “-e” ending of the parent alkane
to “-amine”
•number and name substituents using usual
rules of nomenclature
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Nomenclature
A. Primary Amines
•For the common name, name the alkyl group
bonded to the N atom with the suffix “-amine.”
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Nomenclature
B. Secondary and Tertiary Amines
2o and 3o amines with identical alkyl groups are
named using the prefix “di-” or “tri-”:
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Nomenclature
B. Secondary and Tertiary Amines
HOW TO Name 2o and 3o Amines with Different
Alkyl Groups
Example
Name the following
2o amine:
CH3CHCH3
N H
CH3
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Nomenclature
B. Secondary and Tertiary Amines
HOW TO Name 2o and 3o Amines with Different
Alkyl Groups
•Name the longest alkyl chain bonded to
the N atom as the parent amine.
1 2 3
•The longest chain has 3 C’s,
so it is named propanamine.
Step [1]
•The N is on C2, so it is named
2-propanamine.
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Nomenclature
B. Secondary and Tertiary Amines
HOW TO Name 2o and 3o Amines with Different
Alkyl Groups
Step [2] • Name the other groups on the N as “N-”
alkyl groups.
Answer:
N-methyl-2-propanamine
one methyl
substituent
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Nomenclature
C. Aromatic Amines
•Amines with the N directly bonded to a benzene
ring are named as derivatives of aniline:
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Nomenclature
D. Miscellaneous Nomenclature Facts
•The NH2 group is called an amino group.
•Below are some of the common amine heterocycles:
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Physical Properties
•Many amines have very foul odors like rotting fish,
urine, and bad breath.
•Amines are polar molecules, containing either
polar C—N or polar H—N bonds.
•1o and 2o amines can have intermolecular
hydrogen bonding:
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Physical Properties
•1o and 2o amines have higher boiling points than
compounds that do not have intermolecular
hydrogen bonding.
•1o and 2o amines have lower boiling points than
alcohols, as alcohols have stronger intermolecular
hydrogen bonds.
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Physical Properties
•3o amines have lower boiling points than 1o or
2o amines because they have no N—H bonds.
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Focus on Health & Medicine
Caffeine and Nicotine
•Caffeine and nicotine are widely used stimulants
of the central nervous system that contain
amine heterocycles. They are alkaloids produced
by plants
•Caffeine is a bitter tasting amine found in coffee,
tea, soft drinks, and chocolate.
•Nicotine is a highly toxic amine isolated from
tobacco, which acts as a stimulant in small doses.
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Alkaloids
A. Morphine and Related Alkaloids
•Morphine is obtained from the opium poppy, and
has been used as a pain reliever for centuries. It
is very addictive.
•Codeine is also present in the opium poppy, but in
smaller amounts. It is used for less severe pain,
but it is still very addictive.
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Amines as Bases
•Amines are bases; they are proton (H+) acceptors.
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Amines as Bases
A. Reaction of Amines with Acids
•Amines react with acids (HCl) to form water- soluble salts.
conjugate
conjugate
acid
base
base
acid
Ammonium salt
•The products of the acid/base reaction form an
ammonium salt.
•To name an ammonium salt change the suffix -amine of
the parent amine for the suffix -ammonium. Then add the
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name of the anion.
Focus on Health & Medicine
Ammonium Salts as Useful Salts
•Many amines with medicinal properties are sold
as their ammonium salts, which are transported
through the aqueous bloodstream.
•Some examples include Sudafed, sold as the
salt phenylephrine hydrochloride, shown below.
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Neurotransmitters
•A neurotransmitter is a chemical messenger that
transmits nerve impulses from one neuron to
another.
•The space between the two neurons is called a
synapse.
•The presynaptic neuron releases the neurotransmitter.
•The postsynaptic neuron contains the receptors
that bind the neurotransmitter.
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Neurotransmitters
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Neurotransmitters
A. Norepinephrine and Dopamine
•Below are the structures of the neurotransmitters
norepinephrine and dopamine:
•When norepinephrine levels increase, a person
feels elated, and then manic if levels go too high.
•Dopamine affects the brain processes that control
movement, emotions, and pleasure.
•Patients with Parkinson’s disease have decreased
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levels of dopamine in the body.
Neurotransmitters
B. Serotonin
•Serotonin is synthesized from the amino acid
tryptophan.
•Serotonin is important in mood, sleep, perception,
and temperature regulation.
•A deficiency of serotonin causes depression, so
many antidepressant drugs are selective
serotonin reuptake inhibitors (SSRIs).
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Neurotransmitters
B. Serotonin
•Compounds bufotenin and psilocin are very
similar in structure to serotonin, and they both
cause intense hallucinations.
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Neurotransmitters
C. Acetylcholine and Nicotine Addiction
•Acetylcholine is a quaternary ammonium ion
that serves as a neurotransmitter between neurons
and muscle cells.
•At low concentrations, nicotine binds to acetylcholine receptors, resulting in feelings of wellbeing and alertness.
•This triggers other nerve cells to release dopamine,
which increases the pleasure sensation.
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