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9.2: Background

Difficulty Level: At Grade Created by: CK-12
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The structure of a primary amine.

Amines are organic compounds that contain the element nitrogen. Nitrogen has five electrons, so amines will have a lone electron pair attached to the nitrogen. This lone pair can attract H+ atoms, making amines basic.

The boiling point of amines is higher than that of alkanes because amines are capable of donating and accepting hydrogen bonds. The more electronegative nitrogen attracts electrons more strongly than the hydrogen does, leaving the hydrogens to be more positively charged. These hydrogens can then participate in hydrogen bonding and become attracted to other molecules. In addition, the lone pair on the nitrogen will be attracted to hydrogens on other molecules. Breaking these hydrogen bonds will require additional energy, thus increasing the boiling point of amines. However, the boiling points of amines are generally lower than that of alcohols.

This illustration shows hydrogen bonding in water.

Amines are also relatively soluble in water. Small amines are very soluble in water and are usually sold as solutions at room temperature. This is because all amines can form hydrogen bonds with water. However, when the amine chain is larger, around six carbons, it has to force its way between water molecules. This destroys the hydrogen bonds between the water molecules. The long carbon chain does not participate in hydrogen bonding, so the disrupted hydrogen bonds are not replaced. Now the system is at a higher energy state. In general, systems want to be at the lowest energy state possible to optimize stability. As a result, the system would rather have the larger amines clumped together and the water molecules clumped together in order to increase the number of favorable hydrogen bonds. This effect is greater for larger molecules and so large chains of amines are less soluble than smaller chains.

Amines are often associated with having bad smells, most commonly that of raw fish. The distinctive odor of raw fish is due to the amines that it contains. Another unpleasant smell, decaying flesh, is attributed to two amines, which are appropriately named cadaverine and putresine.

Despite their strong odors, amines are essential for daily life. They are present in amino acids, which create proteins. Many neurotransmitters, such as histamine, are also amines. In industry, amines are also present in dyes, medicines, vitamins, and many other synthesis reactions.

If you want to learn about the nomenclature of amines, visit this website:


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