What is a primary amine?
An amine in which the nitrogen atom is attached to one carbon chain.
How do we name primary amines?
- Identify name of carbon chain attached to amine group. Name is constructed in the form [Name of carbon chain]amine. E.g. CH3CH2NH2: Ethylamine.
- Ignore the amine group and pretend it is an H atom. Name the compound with omitted amine group. Identify the number of the carbon atom attached to amine group. Name is constructed in the form [Carbon number attached to amine group]-amino[Name of compound without amine group]. E.g. CH3CH(NH2)CH3: 2-aminopropane.
What is a secondary amine?
An amine in which the nitrogen atom is attached to two carbon chains.
How do we name secondary amines?
1. Identify the longest (alkyl) chain attached to the amine group.
2. Identify the shortest (alkyl) chain attached to the amine group. Add "N-" as a prefix the the name.
3. Construct the name in the form N-[Name of shortest carbon chain] [Name of longest carbon chain]amine. E.g. CH3CH2NHCH3: N-methyl ethylamine.
What is a tertiary amine?
An amine in which the nitrogen atom is attached to 3 carbon chains.
Why are amines basic?
- Amines are weak bases, just as ammonia.
- Amines have a lone pair of electrons on the N atom in amine group which are able to accept protons by forming dative covalent bonds with them, making them proton acceptors and thus bases.
What is the general fromula for the reaction of an amine with an acid?
Amine +Acid → Amine salt
How do we name amine salts?
1. Take the name of the amine with -amine suffix (e.g. ethylamine). Replace -amine suffix with -ammonium suffix to form name of cation.
2. Identify the name of the anion.
3. Construct the name in the form [Name of cation] [Name of anion].
What are aliphatic amines?
Amine in which the nitrogen atoms are attached to straight carbon chains only.
What are aromatic amines?
Amines in which the nitrogen atoms are attached directly to benzene rings.
How are primary aliphatic amines prepared?
Warming a halogenoalkane with the desired alkyl chain with an excess of ammonia in ethanol solvent.
What type of reaction occurs during preparation of aliphatic amines?
Why is an an excess of ammonia required for the reaction?
To ensure that there are enough ammonia molecules to react with all halogenoalkane molecules in nucleophilic substitution reaction, else the amine groups on the primary amines formed undergo further substitution reactions with to form secondary and eventually tertiary amines.
What is the general formula for the preparation of primary aliphatic amines?
Halogenoalkane + Ammonia → Amine + Hydrogen halide
E.g. Chloroethane + Ammonia → Ethyamine + Hydrogen chloride (CH3CH2Cl + NH3 → Ch3CH2NH2 + HCl)
How are aromatic amines prepared?
Nitrobenzene and other nitroarenes can be reduced to phenylamines. They are heated with a mixture of tin and concentrated HCl under reflux (both make up reducing agent). The excess HCl in the mixture is then neutralised.
What is the equation for the reduction of nitrobenzene?
Nitrobenzene + 6[H] → Phenylamine + 2H2O
(C6H5)NO2 + 6[H] → (C6H5)NH2 + 2H2O
What are amino acids?
Basic chemical building blocks to polypeptides and proteins, which make up a majority of chemicals found in the body and have many uses; including structural functions such as collagen, or physiological functions such as haemoglobin. There are 20 naturally occuring amino acids (α-amino acids) which are arranged in specific sequences to form polymers called polypeptides that form proteins, these sequences are determined by the DNA found in or body.
What is the structure of an α-amino acid?
A central carbon atom is attached to an amine (-NH2) group, a carboxyl (-COOH) group, a hydrogen atom and a residual (-R) group which can be a variety of structures (usually a carbon chain, except for glycine, which is simple an H).
The general formula for an α-amino acid is:
What is a zwitterion?
A dipolar ionic form of an amino acid that is formed by the donation of a hydrogen ion from the carboxyl group to the amino group. Because both charges are present, there is no overall charge.
How are zwitterion formed?
Effectively, because the amine group is basic (proton acceptor) and the carboxyl group is acidic (proton donor) on an amino acid, a proton is transferred from the carboxyl group of an amino acid onto its amine group (if allowed, i.e. in aqueous form). This results in a +ve charge being formed on the amine group and a -ve charge being formed on the carboxyl group that cancel out to give a neutral charge.
What is the isoelectric point?
The pH value at which the amino acid exists as a zwitterion.
What is the significance of the isoelectric point?
There is no net electrical charge at the isoelectric point, this means that zwitterions of an amino acid exist at this pH. Each amino acid has a different isoelectric point due to the influence of different -R groups.
Why are amino acids described as amphoteric?
They can take part in both acid and base reactions.
How can amino acids act as acids?
When put into an environment with pH greater than that of its isoelectric point, an amino acid acts as an acid. The +ve amine (-NH3+) group on the zwitterion donates protons to the base in solution and reacts to form a negatively charged ion.
E.g. RCH(NH3+)COO- + OH- → RCH(NH2)COO- + H2O
How can amino acids act as bases?
When put into an environment with pH lesser than that of its isoelectric point, an amino acid acts as a base. the -ve carboxyl (-COO-) group on the zwitterion accepts protons from the acid in solution and reacts to form a positively charged ion.
RCH(NH3+)COO- + H+ → RCh(NH3+)COOH
What is a condensation reaction?
A reaaction in which two small molecules react together to form a larger molecule with the elimination of a small molecule such as water.
How are polypeptides formed?
When the amine group on one amino acid reacts with the carboxyl group on another in a condensation reaction (omitting a molecule of water), a peptide (amide) bond is formed which joins together the two amino acids to form a dipeptide. This process may repeat as more amino acids are added onto the ends of the growing peptide by condensation reactions, omitting a water molecule per new amino acid joined. This growing chain of amino acids is called a polypeptide and will form the basis of proteins.
What is the formula for the formation of a peptide bond?
H2N-CH(R)-COOH + H2N-CH(R')-COOH →
H2N-CH(R)-CO-NH-CH(R')-COOH + H2O
Note how the -NH2 on R amino acid could react with -COOH on R' amino acid to produce a structural isomer.
What is hydrolysis?
The breaking of bond by reaction with water. Hydrolysis can be catalysed by acid or alkali.
What is the process of acid hydrolysis of a polypeptide?
Conditions: Heat under reflux in a solution of concentrated aqueous HCl.
Reactants: Polypeptide, H2O, H+
Products: The amine salt form of the amino acid.
Equation (Dipeptide equation shown, applies to polypeptides):
H2N-CH(R)-CO-NH-CH(R')-COOH + H2O + 2H+ →
H3N+-CH(R)-COOH + H3N+-CH(R')-COOH