Chapter 18 Amines and Neurotransmitters Based on Material Prepared by Andrea D. Leonard University of Louisiana at Lafayette

Transcription

1 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.

2 Structure and Bonding Amines are organic nitrogen compounds, which are classified by the number of alkyl groups bonded to the N atom. A primary (1 o ) amine has 1 C N bond, and has the general structure RNH 2. A secondary (2 o ) amine has 2 C N bonds, and has the general structure R 2 NH. A tertiary (3 o ) amine has 3 C N bond, and has the general structure R 3 N. 2

3 Structure and Bonding The 1 o, 2 o, and 3 o amine N atom has a lone pair of e, which is omitted in condensed structures. There are quarternary (4 o ) amines, but they do not have a lone pair and bears a positive charge. 3

4 Structure and Bonding The amine N has a trigonal pyramidal shape, with bond angles of ~109.5 o. 4

5 Nomenclature A. Primary Amines 1 o 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 5

6 Nomenclature A. Primary Amines For the common name, name the alkyl group bonded to the N atom with the suffix -amine. 6

7 Nomenclature B. Secondary and Tertiary Amines 2 o and 3 o amines with identical alkyl groups are named using the prefix di- or tri- : 7

8 Nomenclature B. Secondary and Tertiary Amines HOW TO Name 2 o and 3 o Amines with Different Alkyl Groups Example Name the following 2 o amine: CH 3 CHCH 3 N H CH 3 8

9 Nomenclature B. Secondary and Tertiary Amines HOW TO Name 2 o and 3 o Amines with Different Alkyl Groups Name the longest alkyl chain bonded to Step [1] the N atom as the parent amine The longest chain has 3 C s, so it is named propanamine. The N is on C2, so it is named 2-propanamine. 9

10 Nomenclature B. Secondary and Tertiary Amines HOW TO Name 2 o and 3 o 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 10

11 Nomenclature C. Aromatic Amines Amines with the N directly bonded to a benzene ring are named as derivatives of aniline: 11

12 Nomenclature D. Miscellaneous Nomenclature Facts The NH 2 group is called an amino group. Below are some of the common amine heterocycles: 12

13 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. 1 o and 2 o amines can have intermolecular hydrogen bonding: 13

14 Physical Properties 1 o and 2 o amines have higher boiling points than compounds that do not have intermolecular hydrogen bonding. 1 o and 2 o amines have lower boiling points than alcohols, as alcohols have stronger intermolecular hydrogen bonds. 14

15 Physical Properties 3 o amines have lower boiling points than 1 o or 2 o amines because they have no N H bonds. 15

16 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. 16

17 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. 17

18 Amines as Bases Amines are bases; they are proton (H + ) acceptors. 18

19 Amines as Bases A. Reaction of Amines with Acids Amines react with acids (HCl) to form water- soluble salts. conjugate acid conjugate base acid base 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 19 name of the anion.

20 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. 20

21 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. 21

22 Neurotransmitters 22

23 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 levels of dopamine in the body. 23

24 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). 24

25 Neurotransmitters B. Serotonin Compounds bufotenin and psilocin are very similar in structure to serotonin, and they both cause intense hallucinations. 25

26 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. 26