Amines, Amides and Amino Acids Flashcards
Basicity of aliphatic amines
They are weak amines
Lone pair of electrons on Nitrogen can form a dative covalent bond with a H+ (proton)
They are slightly stronger bases than ammonia due to electron donating alkyl groups
Longer chain length = more basic as increasing positive inductive effect, increasing electron density of lone pair of e- on Nitrogen
Basicity of aromatic amines
They are weak amines, weaker than aliphatic
Lone pair of e- on nitrogen feed into ring of delocalised electrons in benzene ring, reducing its e- density
slightly soluble in water due to non-polar benzene ring
Types of bonding present and its effects
London forces
Permanent dipoles
Hydrogen bonding BETWEEN other amine molecules
δ- nitrogen can form hydrogen bonds with the δ+ hydrogens
Higher boiling point that parent alkane
Water soluble
Reaction of amines with water
Form alkaline solutions due to OH- forming
CH3CH2NH2 + H2O –> +NH3CH2CH3 + OH-
Reactivity of aliphatic amines vs aromatic amines
Aliphatic > Amines
Lone pair of electrons on nitrogen feed into benzene ring, which reduces its electron density
Reducing its ability to attract
Reactions of amines with acid and its reverse
CH3CH2NH2 + HCl –> +NH3CH2CH3 + Cl-
Reversible by adding NaOH (strong base)
+NH3CH2CH3 + NaOH –> H2O + Na+ + CH3CH2NH2
Reaction of amines with halogenoalkanes
Nucleophilic substitution (same as halogenoalkanes with ammonia)
CH3CH2NH2 + CH3Cl –> CH3CH2NHCH3 + HCl`
Reaction with acyl chlorides
Nucleophilic Addition-Elimination
Acyl Chlorine + amine –> 2° Amine + HCl
Reaction with Copper(II) sulphate solution
Ligand Exchange
Preparation of Aliphatic Amines (2 ways)
- Nucleophilic Substitution
Halogenoalkane + NH3(aq) –> CH3CH2NH3+ Br-
CH3CH2NH3+Br- + NH3 ⇌ CH3Ch2NH2 + NH4+Br-
- Reduction of Nitriles
Using LiAlH4 in dry ether
CH3C≡N + 4[H] –> CH3CH2NH2
With hydrogen gas in presence of Pt, Pd or Ni catalyst
CH3C≡N + 2H2 –> CH3CH2NH2
Preparation of Aromatic Amines
Create nitrobenzene from Benzene
Electrophilic addition of NO2+
Heat nitrobenzene with conc HCl and Tin, then add NaOH to change NO2 –> NH2
Preparation of Amides from Acyl Chlorides
Acyl Chloride + Amine –> Amide + HCl
or
Acyl Chloride + Excess ammonia –> Amide + HCl
HCl reacts with excess ammonia to form Ammonium chloride
Chemical Properties of Amino acids
- Amphoteric (can act as acid and base) due to Carboxyl group and Amine group
- Amino acids are normally zwitterions (amphoteric)
Condensation reactions of amino acids
Form a peptide bond O=C-NH
COOH group on one amino acid react with NH2 group on other amino acid
Small molecule produced for every peptide bond
Dipeptides = 2 amino acid group make one peptide bond
Tripeptides = 3 amino acid groups make two peptide bonds
Polypeptides (proteins) are formed from condensation polymerisation
How to locate proteins
Using Ninhydrin
React with COLOURLESS amino acids and turns purple then brown
Can locate and identify amino acids
Melting points of amino Acids
High melting points for their size
Ionic attractions between different/other zwitterions that need lots of energy to overcome
Solubility of Amino Acids
Very soluble in water
Zwitterions are attracted to the polar molecules of water
Creates electrostatic solvent-solute interactions
Effect on plane polarised light on Amino Acids
Except glycine
All amino acids have a chiral centre –> optically active
Rotate a plane of plane polarised light and have 2 enantiomers
Hydrolysis of Peptides
Break down peptides into amino acids (reverse of condensation)
Reaction WITH water to reform carboxylic acids and amine groups
Natural hydrolysis in body: broken down by enzymes called proteases
Acid Hydrolysis: Strong acid (HCl) + Heat + Time
Produce the cation of amino acid (NH3+) in acidic conditions from excess HCl
Basic Hydrolysis: Strong Base (NaOH) + Heat + Time
Produce the anion of amino acid (O-) in basic conditions due to excess NaOH
Can form cation salt from Na+ and O-
Analysis of Proteins
1st stage: Hydrolysis of proteins
2nd stage: TLC
Mixture of amino acids is spotted on silica gel
Gel is run in a suitable solvent
Plate is removed and sprayed with ninhydrin
Can either compare the distance travelled with known amino acids or measuring Rf value and comparing with data booklet
Formation of Polyamides
Monomer: Diamine and Carboxylic Aid or amino acid
Examples: Nylon and kevlar
