module 6 (chapter 27) - amino acids, amides and chirality

Question 1

amino acid functional groups

Answer 1

-contains COOH and NH2 group

Question 2

amino acids in the body

Answer 2

• they are also secondary amino acids with the general formula RCH(NH2)COOH
• they react similarly to carboxylic acids and amines

Question 3

amine groups reactions in amino acids

Answer 3

• basic and reacts with acids to make salts

- e.g. alanine reacts with HCl to form an ammonium salt and Cl-

Question 4

carboxylic acid grow reactions in amino acids.

Answer 4

• react with alkalis to form salts and alcohols to form esters
• all amino acids react with aqueous potassium or sodium hydroxide to form a sodium/potassium salt and water
• heat with an alcohol in the presence of concentrated sulphuric acid to form an ester and water
• the acidic conditions also proposes the amine group

Question 5

amides

Answer 5

• produced by the reaction of acyl chlorides with amines or ammonia
• amide groups are formed when the carboxylic acid group is bonded to the amine group
• there can be primary (propanamide), secondary (N-methylethanamide) and tertiary (N,N-dimethylmethanamide)

Question 6

chiral compounds

Answer 6

have four different groups attached to a to a central atom

• this forms optical isomerism (enantiomers)
• sugar and proteins are chiral
• most amino acids are
• optical isomers interact differently with our receptors and so have different tastes and smells

Question 7

what do optical isomers do?

Answer 7

• rotate plane polarised light differently, one clockwise, one anti-clockwise
• a mixture containing 50% of each isomer is racemic and has no effect on plane polarised light as they cancel each other
• therefore, it is pure if it rotates one way or another

Question 8

amines

Answer 8

• they are bases (proton accepter). when an amine accepts a proton, a dative covalent bond is formed between the lone pair on the N and the proton
• as they have a lone pair on the nitrogen atom
• to name primary amines identify the number of carbons in the alkyl chain and add the suffix amine
• to name secondary amines, identify the number of carbons in the longest chain and add the suffix amine. the shorter chain has N added and becomes a prefix

Question 9

amines forming salt

Answer 9

react with acids to form salts

-methylamine by HCl –> methyl ammonium chloride

Question 10

how do we make amines?

Answer 10

• heat a haloalkane with an excess of ethanolic ammonia (not reflux as gas would escape)
• ethanolic acid is ammonia dissolved in ethanol
  1. a bromine addition reaction takes place to form a haloalkane (e.g. bromoethane + ammonia –> ethylammoniumbromide)
  2. react with ammonia to form an amine and NH4+Br-

Question 11

when making amines what happens if the resents are in excess?

Answer 11

• if the haloalkane is in excess the reaction doesn’t stop with the production of a primary amine, the ethylamine will react with the haloalkane making a quaternary amine
• if ammonia is in excess, it makes a primary amine

Question 12

what products do we get when making amines?

Answer 12

• we get a mixture of products as we can’t control what reacts. separate using fractional distillation
• as the amine position number increases boiling point decreases as there are fewer points contact. Eventually you also cannot form hydrogen bonds.

Question 13

nitriles

Answer 13

• C triple bond N
• primary amines can be made by reducing a nitrile
• can either use anhydrous LiAlH4, Na(alcohol) or a nickel catalyst

Question 14

how do you make an aromatic amine?

Answer 14

• convert nitrobenzene
• heat a mixture of the nitro compound with tin and concentration HCl under reflux
• This produces C6H5NH3+
• Then, add sodium hydroxide to remove H+ from the phenyl ammonium ion
• This produces C6H5NH2

Question 15

zwitterion

Answer 15

• a dipolar ion containing both a positive and a negative charge
• a H+ ion is donated form the carboxyl group to the amino group
• there is no overall change
• amino acids only exist as zwitterions at a certain PH (the isostatic point) and is usually around PH6 (this can very depending on the compound)
• they can act as acids and bases
• forms a positive ion in an acidic solution as the carboxyl ion accepts a proton
• forms a negative ion in an alkaline solution as the amine group donates a proton to the OH- ion

Question 16

amines

Answer 16

• organic compound derived from ammonia in which one of more of the hodges atoms have been replaced by a carbon chain or ring
• there are aliphatic where the nitrogen is attached to a straight or branched carbon chain
• there are aromatic when the nitrogen is attached to an aromatic ring

Question 17

what conditions are needed to make amines

Answer 17

• ethanol is used a as a solvent as this prevents any substitution of the haloalkane by Waterloo produce alcohols
• Excess ammonia is used. this reduces further substitution of the amine group to form secondary and tertiary amines

Question 18

how do you make a secondary and tertiary amine?

Answer 18

• the salt formed by reaction of a primary amine and haloalkane must react with sodium hydroxide
• this forms a secondary amine, NaCl and H2O
• tertiary alcohols can be formed by further substitution