Have you ever smelled rotting fish at the beach? Or maybe that sweet smell of dog poop on the bottom of your shoe? If you have, then you have come across amines. Amines are one of smelliest families of organic molecules.
Amines are most easily thought of as close relatives to ammonia (NH3). In fact, the word amine comes from the am- of ammonia. In amines, the hydrogen atoms have been replaced one at a time by hydrocarbon groups.
The basic chemical structure is that of ammonia (NH3) with the key atom being the central nitrogen atom. Try to remember that an amine is just like ammonia because ammonia is a simple molecule to recall. The basic ammonia structure is changed when the hydrogen atoms are replaced by alkyl groups to form amines. You can change one, two or all three of them, and these are called primary, secondary and tertiary amines, respectively.
You can see in the diagrams that the hydrogen atoms have been replaced by an R. This R represents any hydrocarbon side chain and is the generic term that organic chemists use.
The naming of amines is pretty straightforward. Primary amines are called things like methylamine (CH3-NH2) and ethylamine (CH3-CH2-NH2).
Simple secondary and tertiary amines are also easy to name. Dimethylamine is CH3-NH-CH3 and trimethylamine is CH3-N(CH3)-CH3.
Larger amines have names beginning with amino. For example, CH3-CH(NH) -CH2-CH2-CH3 is called 2-aminopentane.
Properties and Reactions
All amines have similar properties and reactions to ammonia, they are just modified by whatever is attached in the R groups. Most of their behavior can be explained by the lone pair of electrons on the nitrogen atom. This lone pair explains why amines are:
- Water Soluble: The small amines of all types are very soluble in water. Larger amines are less soluble because they have long carbon chains that disrupt the hydrogen bonding in water.
- Hydrogen Bonded: All of the amines can form hydrogen bonds with water
- Bases: The lone pair on the nitrogen can take part in coordinate covalent bonding and the amine can donate a pair of electrons to an H+. This means that amines are basic in nature.
So have you ever stopped to think why we often serve lemon wedges with fish? There is a really cool, scientific explanation behind this.
When fish die, bacteria starts to breakdown the amino acids present in the fish's flesh back into amines. Many amines are very smelly, and are the source of many of the 'rotting' odors associated with dead fish. Amines are basic, and mixing them with an acid results in the formation of an amine salt. And this is where the lemon juice comes in.
We are all familiar with the sour taste of a lemon; this taste comes from citric acid in the lemon juice. When we squeeze that lemon wedge onto our fish platters, we are setting up a chain reaction that neutralizes the fishy-smelling amines. Since smell and taste are closely linked, we are also greatly improving the taste of the fish.
Amines in Biology
Amines are found throughout biology. We've already mentioned amino acids, which are the building blocks of proteins. Many neurotransmitters are also amines, including dopamine, serotonin, and histamine. Many drugs are designed to mimic or to interfere with the action of natural amine neurotransmitters.
One drug, methamphetamine, made famous by the hit TV show Breaking Bad is a good example of how a drug interferes with the body's neurotransmitters.
Methamphetamine works by increasing the amount of dopamine, leading to high levels of the chemical in the brain. Dopamine is involved in reward, motivation, and the experience of pleasure and motor function. Methamphetamine's ability to release dopamine rapidly in reward regions of the brain produces the euphoric 'rush' that many users experience. Repeated methamphetamine use can easily lead to addiction and other unpleasant side effects.
Amines closely resemble the ammonia molecule, NH3. Amines can be primary, secondary or tertiary depending on how many hydrogen atoms are replaced by R groups. Amines are responsible for many pungent smells including rotting fish. Amines take part in many acid:base reactions and are very important in biology. Two important classes of amine containing biological molecules are amino acids and neurotransmitters.
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A. Structures and Reactions of Amines
Amines whose structures are derived from ammonia can be categorized as primary amines, secondary amines or primary amines. Since amines have a non-bonding pair of electrons on the nitrogen atom, they generally react as bases. Some biologically relevant amines include noradrenaline and adrenaline. Now that you're familiar with the reactions and structures of amines, see if you can identify them in the activity below.
1. Identify the amine from the compounds given below.
2. Categorize each of the following amines as either a primary amine, secondary amine or tertiary amine.
3. The reaction below is an example of an acid-base reaction. Identify the acid, the base, the conjugate acid and the conjugate base in the reaction.
4. Noradrenaline is a primary amine while adrenaline is a secondary amine. Identify noradrenaline and adrenaline from the structures given below.
B. Naming Primary Amines
Primary amines can be named by writing the name of the alkyl substituent followed by "amine" as the suffix.
CH3 CH2 CH2 NH2
is propylamine because the alkyl group has three carbon atoms.
Provide the names of each of the following primary amines:
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