amino acids, amides and chirality

Question 1

what are amides

Answer 1

has the functional group -CONH2 (derived from carboxylic acid)
-primary amides=NH2 attached to CO secondary=NH attached to CO and other H replaced by an alkyl group

Question 2

what are amino acids?

Answer 2

• have amine group and carboxylic acid group
• they’re amphoteric (have acidic and base properties)
• have organic side chain referenced as R (glycine doesn’t as it just has another H)
• they’re chiral molecules (except glycine) and they rotate plan polarised light

Question 3

what are alpha-amino acids?

Answer 3

NH2/COOH attached to the same carbon

have general formula RCH(NH2)COOH

Question 4

how do amino acids react with acids?

Answer 4

acids react to an amino group to form conjugate acids

e.g. RCH(NH2)COOH + HCl –> RCH(N+H3Cl-)COOH

Question 5

how do amino acids react with alkalis?

Answer 5

alkalis react with the COOH group to form a conjugate base

e.g. RCH(NH2)COOH + NaOH —> RCH(NH2)COO-Na+ +H2O

Question 6

what happens if amino acids react with an alcohol?

Answer 6

-they form an ester and the OH reacts with the COOH whilst using a strong acid catalyst like H2SO4
-e.g. RCH(NH2)COOH+CH3OH—> RCH(NH2)COOCH3 + H2O
(COOH loses a H and combines with the OH in CH3OH to form H2O)

Question 7

define a chiral molecule

Answer 7

4 different groups attached to a C atom and can arrange groups in 2 different ways forming 2 different molecules.

Question 8

how can you create different stereoisomers?

Answer 8

• flip entire molecule over
• flip top two to opposite sides
• flip bottom two to opposite sides

Question 9

what is the link between zwitterions and pH

Answer 9

• if a zwitterion, N+H3 and COO-
• if acidic pH NH2 gains a H+ ion
• if alkaline pH COOH loses a H+ ion

Question 10

how does gas chromatography/mass spectrometry contribute to the analysis of compounds?

Answer 10

1. gas/liquid chromatographs separate the tripeptides
2. mass spectrometer produces a distinctive fragmentation pattern
3. identification using a computer/spectral database

Question 11

State the general formula of an α-amino acid and use it to describe how amino acids can be combined to give a variety of polypeptides and proteins.

Answer 11

idea of polymerisation shown by ‘end bonds’
loss of water
relate variety to different R groups / sequence of amino acids

Question 12

when does a compound NOT fit the general alpha-amino acid formula?

Answer 12

when NH2 and COOH aren’t bonded to the same carbon

Question 13

define a zwitterion

Answer 13

ions with a permanent +/- charge but are neutral overall

Question 14

state suitable reagents and conditions to break down a protein into amino acids

Answer 14

heat under reflux with the addition of a strong acid e.g. HCl as a hydrolysis reaction