Structure and Classification of Amines

• Amines are derivatives of ammonia, the same way that alcohols are derivatives of water

• Amines have a nitrogen, with hydrogens and/or alkyl groups attached

• The shape around the nitrogen is pyrimidal and there is a lone pair of electrons on the nitrogen

• Amines can be classified as 1º, 2º or 3º, just like carbons, based on how many alkyl groups are attached to the nitrogen

NH2

HN N

HN

H

H

Ammonia Primary Amine Secondary Amine Tertiary Amine

Naming Amines• Most simple amines are named by their common names

(which are accepted by IUPAC)• For common names, the alkyl groups attached to the N are

named alphabetically, and amine is added to the end• IUPAC rules are more often used for more complicated

amines- find the longest chain bonded to N, and replace -e in alkane name with amine- number at end nearest N and give number for position of N- the prefixes di, tri etc. are used for multiple amines- when amines are with other functional groups they are called amino groups

NHN

NH2

H

ONH2

H2NNH2

trimethylamine ethylmethylamine 2-butanamine 3-aminobutanal 1,2-ethanediamine

Naming Aromatic and Heterocyclic Amines• Aromatic amines are named as analines• When alkyl groups are attached to the aromatic N, they are

written as N-alkyl at the beginning of the name• As substituents on the ring they are named as amino groups• Heterocyclic amines have one or more nitrogens as part of

the ring and are usually named by their common names- know those that are boxed

NH2HN

NH2

OH

O

analine N-methylanaline ortho-aminobenzoic acid

NH

N

NH

NH

NH N

N

N

N

N NH

N

pyrrolidine pyrrole imidazole piperidine pyridine pyrimidine purine

Physical Properties of Amines

• Primary and secondary amines can H-bond with themselves, so have relatively high boiling points

• However, because the N-H bond is less polar than the O-H bond, amines have lower boiling points than alcohols

• Primary and secondary amines have boiling points similar to aldehydes and ketones

• Tertiary amines can’t H-bond with themselves, and so have boiling points near those of ethers and hydrocarbons

• Smaller amines (less than 5 carbons) are soluble in water

- primary and secondary amines are more soluble than tertiary because they have more H-bonding with water

Basicity of Amines and Amine Salts

• Amines are weak bases that partially ionize in water to form ammonium ions and hydroxide ions

• When treated with acids, amines form salts, without the formation of water

• Quaternary ammonium ions have 4 alkyl groups attached to the nitrogen, and have a permanent positive charge on the N (no H attached to N, so can’t react with bases)

• Amine salts are solids at room temperature and are soluble in water, making them much more useful as medicines

NH2+ H2O NH3

+ OH

N + HClN

H

Cl

Alkaloids• Alkaloids are naturally occurring compounds that contain

nitrogen and have basic properties• They have a wide variety of structures, including simple

amines, aromatic amines, and heterocyclic amines• Some examples of alkaloids are caffeine and the opiates

Structure and Naming of Amides

• Amides are considered derivatives of carboxylic acids• They have an amino group attached to the carbonyl• Most simple amides are known by their common names• For common names the -ic acid is changed to -amide• For IUPAC names the -oic acid is changed to -amide• Alkyl groups attached to the amide nitrogen are indicated

by writing N-alkyl or N,N-dialkyl before the amide name

H NH2

O

NH2

O

NH

O

OH

NH2

O

Br

methanamide(formamide)

ethanamide(acetamide) N-methyl-2-hydroxybutanamide para-bromobenzamide

Physical Properties and Stability of Amides• Primary and secondary amides can H-bond with themselves,

and so have high melting and boiling points• Tertiary amides can’t H-bond with themselves, so have lower

melting and boiling points than primary or secondary• Amides have higher melting and boiling points than carboxylic

acids because they are more flat (due to delocalization of electrons), so they stack better

• Amides (except formamide) are solids at room temperature• Smaller amides (5 carbons or less) are soluble in water• Unlike amines, amides are not basic• They are also very stable (unreactive) compared to esters• This is due to the delocalization of the nonbonded pair of

electrons (through resonance)

NH2

O

NH2

O

NH

O

Preparation of Amides from Carboxylic Acids

• Amines (except tertiary) can react with carboxylic acids to produce amides (amidation)

• The reaction is similar to esterification• Unfortunately, the reaction is of little synthetic use

- amines are bases and will remove a proton from a carboxylic acid, making the acid carbonyl unreactive- primary amides can be formed using ammonia this way, but yields are not great- amides are generally prepared by other methods

OH

O

+ NH3heat

NH2

O

+ H2O

Hydrolysis of Amides• Amides can be hydrolyzed to carboxylic acids using either

acid or base, similar to the hydrolysis of esters• However, amides are much more resistant to hydrolysis

than esters, which is what makes proteins so stable• In the stomach, hydrolysis of amide bonds in proteins is

facilitated by enzyme catalysts• Amide bonds are much more common in medicines than

esters due to this resistance to acid-catalyzed hydrolysis (the drugs are more likely to make it through the stomach)

NH2

O HCl

H2OOH

O

+ NH4 Cl

NH2

O

NaOH

O

O

Na

+ NH3