amino acids, amides and chirality Flashcards
what are the 2 functional groups of amino acids
NH2 (amine)
COOH (carboxylic acid)
what are alpha amino acids
- when both NH2 and COOH are attached to the same carbon
what is the general formula for alpha amino acids
RCH(NH2)COOH
are alpha amino acids chiral? why
- yes because 1 carbon has 4 different substituents
- except glycine where R = H
define a zwitterion
ions which have both a permanent positive and negative charge but are overall neutral
how do zwitterions occur in amino acids?
COOH is depronotated -> COO-
NH2 is protonated -> NH3+
what happens to amino acids in acidic conditions?
gains a proton on the NH2 group
what happens to amino acids in alkaline conditions?
loses a proton from COOH group
what is a peptide linkage
-CONH-
what are the structures of primary and secondary amides
primary - 1 carbon
secondary - 2 carbons
what is the functional group of an amide
-CONH2
what is the difference between an amide and an amine
an amide has a C=O (carbonyl group) unlike amine
what property must a carbon atom have for the molecule to display optical isomerism about that carbon atom?
- 4 different substituents attached to 1 carbon atom
describe the properties of amino acids
- they are amphoteric (acidic and basic properties)
- they are chiral molecules
- rotate plane polarised light
what are the similarities and differences between 2 optical isomers
- same atoms and bonds but they are non-superimposable mirror images of one another
- not identical in all chemical properties
- differ in the way they rotate plane polarised light, may have the same angle but in different directions
what word is used to describe optically active molecules
chiral
give 2 examples of chiral molecules
- alpha amino acids except glycine
- lactic acid
what are enantiomers
- they are mirror images that are non-superimposable (will not overlap)
- they arrange the 4 different groups in 2 ways around the chiral carbon
describe all the different reactions of amino acids
- react with alkali’s to form a conjugate base which combines with a positive ion to produce a salt
- react with acids to form a conjugate acid which then combines with a negative ion to form a salt
- react with alcohols to form esters, requires conc H2SO4
