Amines, amides, amino acids, & proteins - Organic Chem III Flashcards
What are amines derivatives off?
Ammonia - NH3
What do aromatic amines look like?
The N atom directly attached to the benzene ring
Eg/ phenylamine
Why do primary and secondary amines have relatively high melting and boiling points?
A lot of energy is needed to overcome the hydrogen bonds, dipole-dipole forces and London forces between the molecules
N.B. tertiary amines cannot form hydrogen bonds as they don’t have a hydrogen directly attached to the nitrogen
Why are amines soluble in water?
All amines can hydrogen bond with H2O molecules, as the lone pairs of electron on the N atom can hydrogen bond with the positive dipole Hs of H2O
Why does solubility in water decrease as the size of the alkyl chain increase?
Alkyl groups are non-polar/hydrophobic
Solubility decreases as the proportion of the molecule that can form hydrogen bonds decreases
What smell do amines have?
Fishy smell
Vapours turn damp red litmus paper blue
What is the order of basicity?
Most basic: 3° > 2° > 1° > NH3 > aromatic least basic
Can this order of basicity be explained?
Alkyl groups are electron releasing. The greater the number of alkyl groups attached to the N atom, the greater the electron density on the N atom, so the lone pair can more readily accept a H+
The lone pair of electron on the N atom is at the correct orientation to overlap with the delocalised π system of the benzene ring. The lone pair of electrons is therefore not localised on the N atom, and is less able to accept a H+
Which is the stronger base, methylamine or diethylamine?
Diethylamine
- More alkyl groups attached to the N atom, the greater the electron density on the N atom, so the lone pair can more readily accept a H+
Which is the stronger base, ammonia or phenylmethylamine?
Phenylmethylamine
- Alkyl groups are electron releasing. The greater the number of alkyl groups attached to the N atom, the greater the electron density on the N atom, so the lone pair can more readily accept a H+
What is the reaction between ethylamine and hydrochloric acid
C2H5NH2 + HCl -> C2H5NH3Cl
How could you liberate the free amine from the salt?
Add NaOH
What is the test for NH4+?
NH4+ + OH- –> (warm) NH3 + H2O
- pungent smell, damp red litmus paper blue
What does the SN1 mechanism look like?
Favoured by tertiary halogenoalkanes
1. The first NH3 acts as a nucleophile
2. The second NH3 acts as a base (a proton acceptor)
What does the SN2 mechanism look like?
Favoured by primary halogenoalkanes
Why is there a problem with this reaction?
The amine produced can also act as a nucleophile
- You end up with a mixture of liquid products - so you’d separate them by fractional distillation
What is a more controlled method of preparation of a primary aliphatic amines to reduce a nitrile?
Eg/ CH3C≡N + 2H2 –> (Ni catalyst, 150) CH3CH2NH2
Eg/ CH3C≡N + 4[H] –> (LiAlH4 in dry ether, room temp.) CH3CH2NH2
Why can’t the above methods be used to prepare an aromatic amine?
The ammonia, with its lone pair of electron will be repelled by the electron rich benzene ring
How could you produce an aromatic amine?
To produce an aromatic amine - use tin in conc. HCl, heat under reflux
Nitrobenzene + 6[H] –> phenylamine + 2H2O
What is the reaction between ethanoyl chloride and butylamine:
Eg/ butylamine + CH3COCl –> N-butylethanamide + HCl
What is the reaction between phenylamine and ethanoyl chloride:
Eg/ phenylamine + CH3COCl –> N-phenylethanamide + HCl
What are polyamides formed by?
Results from the condensation of diacylchlorides (or dicarboxylic acids) and diamines to form the substituted amine group
What is a copolymer?
A copolymer results when a diacyl chloride reacts with a diamine to form repeating substituted amide groups. The monomers each have two functional groups (bifunctional)
What are amino acids?
Compounds that contain both a basic -NH2 group and an acidic -COOH group. Amino acids are the chief constituents of proteins.
NH2CH(R)COOH
Why are amino acids chiral?
Attached to 4 groups. With the exception of the simplest amino acid, glycine, all amino acids show optical activity. Therefore each amino acid can exist in two forms that are non-superimposable mirror images of each other.
What are the physical properties of amino acids?
- Solids with relatively high melting points
- Soluble in water but have low solubility in non-polar solvents
- Exists as zwitterions (internal salts): a lot of energy is needed to overcome the strong electrostatic forces of attraction between the oppositely charged ions in neighbouring zwitterions
What is the reaction of amino acid with acid (H+):
NH2CH2COOH + H+ –> NH3+CH2COOH
What is the reaction of amino acid with base (OH-):
NH2CH2COOH + OH- –> NH2CH2COO- + H2O
What is the reaction of amino acid undergoing esterification with ethanol (and conc. H2SO4)
NH2CH2COOH + CH3CH2OH ⇌ NH2CH2COOCH2CH3 + H2O
What is the reaction of amino acid undergoing acylation with ethanoyl chloride
NH2CH2COOH + CH3COCl –> CH3CONHCH2COOH + HCl
How can a dipeptide be formed?
A didpeptide is a dimer formed from two amino acids
CONH - peptide bond
How do you hydrolyse a peptide?
This is done by refluxing with hydrochloric acid to break down the peptide bonds
How can peptides and proteins be hydrolysed into their constituent amino acids?
By adding conc. HCl
Then individual amino acids can then be separated using either paper chromatography or TLC
What does the rate at which a compound moves up the TLC plate depend on?
Its solubility in the chosen solvent. Each compound within a mixture would have a different solubility so they separate as the solvent moves up the plate
