carboxylic acids and esters

carboxylic acids

have an OH group bonded to the carbonyl carbon atoms

weak acids

parent compounds of esters and amines

physical properties of carboxylic acids

higher boiling points than alcohols

form H bonding pairs

solubility in water depends on R

chemical properties of carboxylic acids

acidic due to stability of carboxylate anion

strongly resist oxidation

reduction of carboxylic acids

requires strong reducing agents - LiAlH4

attack at carboxylate anion is difficult

ester formation

carboxylic acids react with alcohols

way to remove water

Dean-Stark apparatus

esters

have an OR group bonded to carbonyl

physical properties of esters

can accept H bonds

low boiling points

low weight esters are water soluble

chemical reactions

readily reduced - give 2 alcohol products

H+ catalysed hydrolysis of esters

reverse ester formation - excess water pushed equilibrium to the right

base-mediated hydrolysis

ester hydrolysis in aqueous is irreversible - saponification

triacylglycerols

3 acyl units are contributed to by 2/3 different fatty acids

saturated fatty acids

pack efficiently into crystals and have high melting points

unsaturated fatty acids

double bonds are all cis which interferes with packing and lowers melting points

economic relevance

1. biodiesel

2. omega-3 fatty acids

monophosphate esters

alcohol + phosphoric acid

doubly ionised at biological pH

triphosphate ester (ATP)

formed from the reaction of an alcohol and triphosphoric acid

ATP and energy

triphosphates are amongst the most energy-rich substances

food and energy - stage 1

bulk food is digested in the mouth, stomach, and small intestine to yield small molecules

stage 2

sugars fatty acids and amino acid molecules are degraded in cytoplasm of cells to yield acetyl-SCoA

stage 3

acetyl-SCoA is oxidised inside mitochondria by citric acid cycle to yield CO2 and reduce coenzymes

stage 4

the energy transferred to the reduced coenzymes (NADH, FADH2) in stage 3 is used to make ATP by the coupled pathways of electron transport and oxidative phosphorylatium