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Amine: Definition, Structure, Reactions & Formula

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  • 0:00 Definition
  • 0:30 Chemical Structure
  • 1:55 Properties and Reactions
  • 2:40 Example
  • 3:30 Amines in Biology
  • 4:20 Lesson Summary
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Lesson Transcript
Instructor
Nicola McDougal

Nicky has taught a variety of chemistry courses at college level. Nicky has a PhD in Physical Chemistry.

Expert Contributor
Ronald Okoth

Ronald received his PhD. from Brown University in Providence RI. Ronald has taught college level chemistry.

What does the fried fish you eat and dog poop have in common? The answer is amines. In this lesson, we will learn about the chemical structure of amines and how they react.

Definition

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.

Chemical Structure

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You can see in the diagrams that the hydrogen atoms have been replaced by an R. This R represents any hydrocarbon side chain and is the generic term that organic chemists use.

Primary amine with one hydrogen atom replaced with an R group
Diagram of a Primary Amine

Secondary amine with two hydrogen atoms replaced with an R group
Diagram of a Secondary Amine

Tertiary amine with all three hydrogen atoms replaced with an R group
Diagram of a Tertiary Amine

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.

Example

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.

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Additional Activities

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.

For example;

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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