Acid & Base Behavior of Amines: Definition & Structure

Instructor: Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

This lesson will review the definitions for acids and bases and discuss the acid and base properties of amines. We'll explain how the structure of amines contributes to their function as a base in many solutions.

What Are Acids and Bases

Acids and bases can be scary substances, especially since a lot of the time, they're pretty corrosive and can cause damage to human tissue and structures alike. Despite the potential dangers, acids and bases are found in many different aspects of our lives, from our car batteries to the bleach with which we clean our kitchen counters and bathtubs. Even the inside of our stomach is equipped with a strong acid to break down our food. But, what are acids and bases in chemistry?

Chemists use three definitions of acids and bases:

  • The Arrhenius definition
  • The Bronsted-Lowry definition
  • The Lewis definition

The Arrhenius definition defines acids as molecules that can donate a hydrogen ion and bases as molecules that can donate a hydroxide ion. Secondly, according to the Bronsted-Lowry definition, acids can donate a hydrogen ion and bases accept a hydrogen ion. Lastly, in the Lewis definition, Lewis acids are electron pair acceptors whereas Lewis bases are electron pair donors. Let's now take a closer look at amines acting as bases.

Amines as Bases

Amines are functional groups that contain a nitrogen atom connected to other groups with a single bond. Primary amines are connected to one carbon and two hydrogen atoms, whereas secondary amines are connected to two carbons and one hydrogen and tertiary amines are connected to three carbon groups.

Amines can act as bases in either the Bronsted Lowry definition or the Lewis definition. But before we examine the basic properties of amines, you might be wondering the very fair question: why should you care about any of this?

Well, it turns out that amines are essential to keeping your body alive. Proteins make up the structure of all the cells in your body--particularly your muscles--and let you to carry out many different functions. Proteins are made of amino acids, which are molecules with the amine functional group. Amines also show up in our DNA, the genetic code of all of our traits.

Now, let's jump back to amines as bases. Amines have a nitrogen atom bound to some combination of carbon and hydrogen atoms and are able to make three bonds total. Amines react with acids to accept a hydrogen ion, making them an acid according to the Bronsted-Lowry definition. This gives the amine a positive charge.

Amines can accept a hydrogen atom to act as a Bronsted Lowry base
amines and acids

Amines are also a base in the Lewis definition. An amine group has a lone pair of electrons when it forms three bonds. It can donate these electrons to other molecules, making it a base in the Lewis definition too.

Amines are generally weak bases, but their intensity depends on the structures in which they are bound to. Amines that have double or triple bonds or are connected to a benzene ring with electron delocalization tend to be weaker bases. This is because the lone electron pair is stabilized through delocalization and less likely to be donated to form an additional bond. Now let's take a quick look at amines acting as acids.

Amines as Acids

Primary and secondary amines are also very weak acids according to the Bronsted-Lowry definition and the Lewis definition. Primary and secondary amines can donate a hydrogen atom in solution, making them acids according to the Bronsted-Lowry definition.

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