amino acids, amides and chirality

Question 1

what are the 2 functional groups of amino acids

Answer 1

NH2 (amine)
COOH (carboxylic acid)

Question 2

what are alpha amino acids

Answer 2

• when both NH2 and COOH are attached to the same carbon

Question 3

what is the general formula for alpha amino acids

Answer 3

RCH(NH2)COOH

Question 4

are alpha amino acids chiral? why

Answer 4

• yes because 1 carbon has 4 different substituents
• except glycine where R = H

Question 5

define a zwitterion

Answer 5

ions which have both a permanent positive and negative charge but are overall neutral

Question 6

how do zwitterions occur in amino acids?

Answer 6

COOH is depronotated -> COO-
NH2 is protonated -> NH3+

Question 7

what happens to amino acids in acidic conditions?

Answer 7

gains a proton on the NH2 group

Question 8

what happens to amino acids in alkaline conditions?

Answer 8

loses a proton from COOH group

Question 9

what is a peptide linkage

Answer 9

-CONH-

Question 10

what are the structures of primary and secondary amides

Answer 10

primary - 1 carbon
secondary - 2 carbons

Question 11

what is the functional group of an amide

Answer 11

-CONH2

Question 12

what is the difference between an amide and an amine

Answer 12

an amide has a C=O (carbonyl group) unlike amine

Question 13

what property must a carbon atom have for the molecule to display optical isomerism about that carbon atom?

Answer 13

• 4 different substituents attached to 1 carbon atom

Question 14

describe the properties of amino acids

Answer 14

1. they are amphoteric (acidic and basic properties)
2. they are chiral molecules
3. rotate plane polarised light

Question 15

what are the similarities and differences between 2 optical isomers

Answer 15

• 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

Question 16

what word is used to describe optically active molecules

Answer 16

chiral

Question 17

give 2 examples of chiral molecules

Answer 17

1. alpha amino acids except glycine
2. lactic acid

Question 18

what are enantiomers

Answer 18

• they are mirror images that are non-superimposable (will not overlap)
• they arrange the 4 different groups in 2 ways around the chiral carbon

Question 19

describe all the different reactions of amino acids

Answer 19

1. react with alkali’s to form a conjugate base which combines with a positive ion to produce a salt
2. react with acids to form a conjugate acid which then combines with a negative ion to form a salt
3. react with alcohols to form esters, requires conc H2SO4