6.2.2 Amino Acids, Amides and Chirality
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what is an amino acid
an organic compound containing both an amine, NH2, and a carboxylic, COOH, group
what amino acids are in the body
• 20 amino acids, ALL ALPHA α • as the amine group is attached to the α carbon • the second one away from the COOH
what do all amino acids differ by
• all differ by the side chain R
what is the general formula of amino acids
RCH(NH2)COOH
what does an amino acid look like
H2N-CHR-COOH
what properties do amino acids have
• contain NH2: so BASIC • contain COOH: so ACIDIC
how do amino acids react due to the amine group
• react with acids • to form salts
how does an amino NH2-CHR-COOH react with HCl
NH2-CHR-COOH + HCl → Cl- NH3+-CHR-COOH • forms the salt, as NH2 gains a proton, becomes NH3+, and the Cl- is just floating nearby
how do amino acids react due to the COOH group
• react with alkalis to form a salt • react with alcohols, in the presence of H2SO4 to form esters
how does NH2-CHR-COOH react with NaOH
NH2-CHR-COOH + NaOH → NH2-CHR-COO-Na+ + H2O • forms the salt, as COOH loses its H, and forms COO- ion, and is replaced with Na+
how does NH2-CHR-COOH react with ethanol
NH2-CHR-COOH + C2H5OH + H+ → NH3+-CHR-COOC2H5 + H2O • the alcohol and the carboxylic acid combine to form an ester • the presence of H2SO4 protonates the amine group to NH3+
how are amides formed
the product of a reaction between acyl chlorides and ammonia/amines
what is the amide functional group
O=C-N
what are examples of amide bonds in nature
peptide bonds in proteins
how can amides be classified
dependent on the amount of carbons attached to the N - e.g. 1°/2°
what is a primary amide, and how is it names
• only has 1 carbon bonded to the N, other 2 bonds are Hs • the amount of carbons + amide • e.g. CH3CH2C(=O)NH2 would be propanamide
what is a secondary amide, and how is it named
• has 2 carbons bonded to the N, the other bond is a H • whichever alkyl group is attached, is referred to as N-linked • e.g. CH3-C(=O)NHCH3 would be N-methyl ethanamide
what is a tertiary amide, and how is it named
• has 3 carbons bonded to the nitrogen • same naming as before, but refer to each N link separately, IN ALPHABETICAL ORDER • e.g. H-C(=O)CH3(CH3) would be N,N-dimethyl methanamide
what is a stereoisomer
compounds with the same structural formula but a different arrangement of atoms
what is a type of stereoisomer found in amino acids
optical isomers
what molecules are optical isomers found in
found in molecules containing chiral centres - labelled with asterisk *
what is a chiral centre
a carbon atom that is attached to 4 different atoms/groups of atoms • for each chiral centre, one pair of optical isomers exist
what is an optical isomer
2 non-superimposable mirror image structures - also known as enantiomers
what are examples of optical isomers
• exist widely in naturally occurring organic molecules • e.g. sugars, proteins, nucleic acids • EXCEPT GLYCINE: has 2 Hs as groups, but all other amino acids contain them • also not reserved to carbon atoms, but any centre that has attachments that can be arranged as 2-nonsuperiposable mirror image forms