Chemistry » Organic Chemistry » Amines and Amides

Amines and Amides

Amines and Amides

Amines are molecules that contain carbon-nitrogen bonds. The nitrogen atom in an amine has a lone pair of electrons and three bonds to other atoms, either carbon or hydrogen. Various nomenclatures are used to derive names for amines, but all involve the class-identifying suffix –ine as illustrated here for a few simple examples:

Three structures are shown, each with a red, central N atom which has a pair of electron dots indicated in red above the N atoms. The first structure is labeled methyl amine. To the left of the N, a C H subscript 3 group is bonded. H atoms are bonded to the right and bottom of the central N atom. The second structure is labeled dimethyl amine. This structure has C H subscript 3 groups bonded to the left and right of the N atom and a single H atom is bonded below. The third structure is labeled trimethyl amine, which has C H subscript 3 groups bonded to the left, right, and below the central N atom.

In some amines, the nitrogen atom replaces a carbon atom in an aromatic hydrocarbon. Pyridine (see the figure below) is one such heterocyclic amine. A heterocyclic compound contains atoms of two or more different elements in its ring structure.

A molecular structure is shown. A ring of five C atoms and one N atom is shown with alternating double bonds. Single H atoms are bonded, appearing at the outside of the ring on each C atom. The N atom has an unshared electron pair shown on the N atom on the outer side of the ring. The N atom, electron dot pair, and bonds connected to it in the ring are shown in red.

The illustration shows one of the resonance structures of pyridine.

Like ammonia, amines are weak bases due to the lone pair of electrons on their nitrogen atoms:

Two reactions are shown. In the first, ammonia reacts with H superscript plus. An unshared pair of electron dots sits above the N atom. To the left, right, and bottom, H atoms are bonded. This is followed by a plus symbol and an H atom with a superscript plus symbol. To the right of the reaction arrow, ammonium ion is shown in brackets with a superscript plus symbol outside. Inside the brackets, the N atom is shown with H atoms bonded on all four sides. In a very similar second reaction, methyl amine reacts with H superscript plus to yield methyl ammonium ion. The methyl amine structure is like ammonia except a C H subscript 3 group is attached in place of the left most H atom in the structure. Similarly, the resulting methyl ammonium ion is represented in brackets with a superscript plus symbol appearing outside. Inside, the structure is similar to that of methyl amine except that an H atom appears at the top of the N atom where the unshared electron pair was previously shown.

The basicity of an amine’s nitrogen atom plays an important role in much of the compound’s chemistry. Amine functional groups are found in a wide variety of compounds, including natural and synthetic dyes, polymers, vitamins, and medications such as penicillin and codeine. They are also found in many molecules essential to life, such as amino acids, hormones, neurotransmitters, and DNA.

Amides are molecules that contain nitrogen atoms connected to the carbon atom of a carbonyl group. Like amines, various nomenclature rules may be used to name amides, but all include use of the class-specific suffix -amide:

This figure shows three structures. Two examples are provided. The basic structure has an H atom or R group bonded to a C atom which is double bonded to an O atom. The O atom as two sets of electron dots. The C atom is bonded to an N atom which in turn is bonded to two R groups or two H atoms. The N atom as one set of electron dots. The next structure includes acetamide, which has C H subscript 3 bonded to a C atom with a doubly bonded O atom. The second C atom is also bonded to N H subscript 2. Hexanamide has a hydrocarbon chain of length 6 involving all single bonds. The condensed structure is shown here. To the sixth C atom at the right end of the chain, an O atom is double bonded and an N H subscript 2 group is single bonded.

Amides can be produced when carboxylic acids react with amines or ammonia in a process called amidation. A water molecule is eliminated from the reaction, and the amide is formed from the remaining pieces of the carboxylic acid and the amine (note the similarity to formation of an ester from a carboxylic acid and an alcohol discussed in the previous section):

A chemical reaction is shown between a carboxylic acid and amine to form an amide and water. Structures are shown. The carboxylic acid is shown as a C H subscript 3 group bonded to a C H subscript 2 group bonded to a C atom with a double bonded O atom above and an O H group bonded to the right. There is a plus sign. The amine is shown as an N atom with two H atoms bonded to the bottom and left sides. A C H subscript 3 group is bonded to the right side of the N atom. To the right of an arrow, an amide is shown as a C H subscript 3 group bonded to a C H subscript 2 group bonded to a C atom which is double bonded to an O atom above and an N with an H atom bonded below. The N atom is bonded to a C H subscript 3 group. The final product indicated after a plus sign is water, H subscript 2 O.

The reaction between amines and carboxylic acids to form amides is biologically important. It is through this reaction that amino acids (molecules containing both amine and carboxylic acid substituents) link together in a polymer to form proteins.

The table here summarizes the structures discussed in this tutorial:

This table provides compound names, structures with functional groups in red, and examples that include formulas, structural formulas, ball-and-stick models, and names. Compound names include alkene, alkyne, alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, and amide. Alkenes have a double bond. A formula is C subscript 2 H subscript 4 which is named ethene. The ball-and-stick model shows two black balls forming a double bond and each is bonded to two white balls. Alkynes have a triple bond. A formula is C subscript 2 H subscript 2 which is named ethyne. The ball-and-stick model shows two black balls with a triple bond between them each bonded to one white ball. Alcohols have an O H group. The O has two pairs of electron dots. A formula is C H subscript 3 C H subscript 2 O H which is named ethanol. The ball-and-stick model shows two black balls and one red ball bonded to each other with a single bond. There are four white balls visible. Ethers have an O atom in the structure between two R groups. The O atom has two sets of electron dots. A formula is ( C subscript 2 H subscript 5 ) subscript 2 O which is named ethanal. The ball-and-stick model shows two black balls bonded to a red ball which is bonded to two more black balls. All bonds are single. There are five white balls visible. Aldehydes have a C atom to which a double bonded O and an H and an R are included in the structure. The O atom has two sets of electron dots. A formula is C H subscript 3 C H O which is named Ethanal. The ball-and-stick model shows two black bonds bonded to two red balls. The ball-and-stick model shows two black balls bonded with a single bond and the second black ball forms a double bond with a red ball. There are three white balls visible. Ketones show a C atom to which a double bonded O is attached. The left side of the C atom is bonded to R and the right side is bonded to R prime. The O atom as two sets of electron dots. The formula is C H subscript 3 C O C H subscript 2 C H subscript 3 and is named methyl ethyl ketone. The ball-and-stick models shows four black balls all forming single bonds with each other. The second black ball forms a double bond with a red ball. There are five white balls visible. Carboxylic acids have a C to which a double bonded O and an O H are included in the structure. Each O atom has two sets of electron dots. A formula is C H subscript 3 C O O H which is named ethanoic or acetic acid. The ball-and-stick model shows two black balls and one red ball forming single bonds with each other. The second black ball also forms a double bond with another red ball. Three white balls are visible. Esters have a C atom which forms a double bond with an O atom and single bond with another O atom which has an attached hydrocarbon group in the structure. Each O atom has two sets of electron dots. A formula is C H subscript 3 C O subscript 2 C H subscript 2 C H subscript 3 which is named ethyl acetate. The ball-and-stick model shows two black balls, a red ball, and two more black balls forming single bonds with each other. The second black ball forms a double bond with another red ball. There are five white balls visible. Amines have an N atom in the structure to which three hydrocarbon groups, two hydrocarbon groups and one H atom, or one hydrocarbon group and two H atoms may be bonded. Each n has a single set of electron dots. A formula is C subscript 2 H subscript 5 N H subscript 2 which is named ethylamine. The ball-and-stick model shows two black balls and one blue ball forming single bonds with each other. There are five white balls visible. Amides have a C to which a double bonded O and single N incorporated in a structure between two hydrocarbon groups. One hydrocarbon group is bonded to the C, the other to the N. Amides can also have a H atom bonded to the N. The O atom as two sets of electron dots, and the N atom has one set. A formula is C H subscript 3 C O N H subscript 2 which is named ethanamide or acetamide. The ball-and-stick model shows two black balls and one blue ball forming single bonds with each other. The second black ball forms a double bond with one red ball. There are four white balls visible.

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