Ch. 2 - Molecular RepresentationsWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins
Johnny Betancourt

An amine is a derivative of ammonia (NH3). Where ammonia is composed of a nitrogen with three hydrogens attached, at least one hydrogen is replaced by a carbon chain. 

Structure of an amine: 

An amine functional group is a nitrogen attached to at least one hydrocarbon. Like alkyl halides and alcohols, amines get degrees—the only difference is that amines get their degrees based on how many carbons are directly attached to the nitrogen. Assuming “R” stands for a carbon, let’s see what those structures look like:

4 degrees of amine RNH2, R2NH, R3NH, R4N+4 degrees of amine RNH2, R2NH, R3NH, R4N+

From left to right: primary amine (1º), secondary amine (2º), tertiary amine 3º, quaternary amine (4º). Quaternary amines will always have a positive formal charge on the nitrogen. 

Hyrbidization and geometry: 

Are those structures drawn above the whole story? Nope! They don’t account for VSEPR! Recall that “Bond sites will repel each other as much as possible.” Let’s figure out the hybridization and geometry of the following amine:

Trimethylamine hybridization and geometry answerTrimethylamine hybridization and geometry answer

A non-quaternary amine has three R-groups or hydrogens and one lone pair. Since it’s got four groups, it’s sp3-hybridized. When an atom has three atoms attached and one lone pair, that atom’s geometry will be trigonal pyramidal. This is different from an atom that has four atoms attached and no lone pair; that atom would be tetrahedral.

Amine Chemistry:

Acid-Base reactions:

Do you expect amines to be acidic or basic? Let’s see what it looks like when ammonia reacts with hydrochloric acid:NH3 reacting with HX to form NH4-XNH3 reacting with HX to form NH4-X

Since reactions always move in the direction of the weaker acid, we can see that this reaction should proceed to the right. The basic nitrogen will remove the acidic hydrogen from the chlorine, and an ammonium salt (ammonium ion) will form. Remember that the direction of equilibrium will be from more acidic to less acidic. 

Substitution:

What does it look like when an amine acts as a nucleophile? An amine can perform an SN2 reaction when a molecule has a good-enough leaving group. Let’s look at ethylamine (a primary amine) reacting with chloromethane in an amine alkylation reaction: 

Ethylamine and chloromethane substitution reactionEthylamine and chloromethane substitution reaction

Types of amines:

Amines are extremely common in Organic Chemistry. Let’s look at two examples of types of amines:

Aniline and butylamineAniline and butylamine

The molecule on the left is called aniline, and it has an amino group on the aromatic molecule benzene ("amino" is the name that we give to an amine that is a substituent).  The reactivity and chemical properties of aromatic amines are a bit different from those of an aliphatic amine (aka alkyl amine) like the n-butylamine on the right. Amines can act as activating groups on benzene, but we’ll talk more about that in Orgo 2 in EAS

Where can amines be found in nature? You can find amines in amino acids, amine hormones, alkaloids produced by plants, and tons more places. Are you familiar with the smell of decaying fish? You can thank amines like trimethylamine for that one.

To learn about other nitrogen-containing organic compounds, like those with carbonyls, check out my videos on functional groups. Good luck studying! 



Johnny Betancourt

Johnny got his start tutoring Organic in 2006 when he was a Teaching Assistant. He graduated in Chemistry from FIU and finished up his UF Doctor of Pharmacy last year. He now enjoys helping thousands of students crush mechanisms, while moonlighting as a clinical pharmacist on weekends.