Acids, Esters and Amides

Question 1

carboxylic acids, esters and amides are similar in structure

Answer 1

higher boiling point than alkanes

Question 2

carboxylic acids - odour and physical and chemical characteristics

Answer 2

colourless liquids with odours
5-10 carbons have a goaty odour
10 carbons are wav like solids
odour decreases with size (decrease in volatility)
1-4 carbons are miscible with water due to H bonding with carbonyl group - two H bond acceptors (O)
as length increases, dipole forces decrease and dispersion forces increase
typically weak acids - partially dissociate to H+ and RCOO- (carboxylate anions). resonance is possible and thus they are more acidic than alcohols

Question 3

Esters - odour and physical and chemical characteristics

Answer 3

colourless, volatile liquids with pleasant odours
derived from carboxylic acids (OH to OR - loss of H, cannot hydrogen bond in ester and therefore lower BP than carboxylic acids)
can form H bonds with water (fairly soluble when small)

Question 4

naming carboxylic acids

Answer 4

propanoic acid

Question 5

naming esters

Answer 5

ethyl acetate

alkyl group first and parent acid second

Question 6

ester synthesis

Answer 6

carboxylic acids becomes an ester using acid catalyst and alcohol
Fischer esterification

Question 7

amide synthesis

Answer 7

carboxylic acid + amine = amide
this is usually an activated acid (eg. acid chloride)
must heat more than 160 degrees c for reaction otherwise the amine deprotenates the acid
protected amine is a poor nucleophile
carboxylate is a poor electrophile
H bond donors (most primary amides, least secondary amides - trend in BP)
resonance means that N-C is a partial doublish bond and this blocks some rotation

Question 8

hydrolysis of esters and amides

Answer 8

hydrolysed to produce carboxylic acid and alcohol or amine
add excess water to push equilibrium back
acid or base catalysed
amides are more stable than esters
amides need to be catalysed (esters don’t) - NH2 does not break off as easily as NH3+ which OH replaces
reactivity of carboxylic acids depends on strength of the acetyl bound substituent
NH2 (most basic) than OR or OH

Question 9

nucleophilic substitution at the carbonyl group

Answer 9

electrons move from the oxygens to the positive end of the carbonyl, breaking the double bond. electrons move from the (once) carbonyl bond to a bond, establishing a different carbonyl group

this substitution can form amides

Question 10

what is a leaving group?

Answer 10

it can stabilise negative charge and is called “good”
Cl- in HCL
low pKa = happy, stable therefore Cl- is good
this X group affects rate