carboxylic acids Flashcards
what is a carboxyl group?
carbonyl group + hydroxyl group
properties of carboxyl group
- carbon hybridised sp2
- methanoic acid: formic acid
- ehtanoic acid: acetic acid
- carboxyl group + phenyl group -> benzoic acid
- contain polar groups -> strongly polar
- act as both donor and acceptor for protons with other acid molecules (-COOH group)
- higher boiling points than corresponding alcohols
- can form dimers
- longer chain -> less soluble in water
how is a carboxyl group derived?
- derived from oxidation of aldehyde
- acetic acid -> ethanol oxidised first to acetaldehyde (ehtanal) then to ehtanoic acid
what is the properties of acidity of organic compounds?
- weak acids
- break down with water in respective ion and hydronium ion
- conjugated base is stabilised by resonance in 2 electronegative oxygens (negative charge on structure can shift between oxygen atoms)
- hydrocarbon chain has inductive effect -> the longer the chain the more electron donating the effect and less stabilised the conjugate base
- react with bases to form salts
describe anhydrides and their reactions
acid derivatives / can be symmetric or asymmetric
- 2 acid molecules undergo condensation and lose water molecule (dehydrating conditions)
- highly reactive with nucleophiles -> give 2 molecules of acid in highly exergonic reaction
- found in biological intermediates as they pack large amounts of energy
describe acyl-chlorides
R-CO group:
- replacement of OH in carboxyl group with chlorine yields acid chloride
- Cl electronegativity and leaving group properties make molecule more reactive in nucleophilic substitution
what are the main polyfunctional organic acids?
α-hydroxyacids
dicarboxylic acids
α-ketoacids
describe α-hydroxyacids and give examples
always have α-hydroxyl (-OH) and carboxylic acid groups -glycolic acid (sugar cane) -lactic acid -tartaric acid (grapes) magic acid (apples) -citric acids
describe dicarboxylic acids and give examples
contain 2 carboxyl groups
first pKa is lower than the second because 2nd ionisation introduces negative second charge on the molecule and charge repulsion
-Oxalic acid (2-COOH bonded together - ethanedioic acid)
-Malonic acid (one methylene bridge - propanedioic)
- Succinic acid (2 methylenes - butanedioic)
- Glutaric acid (3 - pentanedioic)
- Adipic acid (4 - hexanedioic)
- Pimelic acid (5 - heptanedioic)
*increase by 1 C between carboxylic groups
Oh My, Such Good Apple Pie!
describe α-ketoacids and give examples
carboxylic acids that have keto group directly attached to COOH:
- can undergo modification at keto group
- has ketone and acid properties
- can be reduced to hydroxyl and vice versa, n of bonds to H and O remains the same
- pyruvic acid
how are esters synthesised?
- condensation of acid and alcohol (acid can be organic or inorganic)
- equilibrium reaction (excess of alcohol is used to produce large amounts of ester)
- not favoured by aqueous environment -> release of water is energetically unfavourable
- reversible -> molecules can be formed and broken down - acyl chlorides are extremely reactive in water -> not good reactants in living cells
- anhydrides are preferred especially mixed with phosphoric acid
- acyl chlorides are extremely reactive in water -> not good reactants in living cells
- with inorganic acids: phosphate esters
- link nucleotides in nucleic acids
- modify proteins and signal variation in environment
- add negative charges to metabolites and trap them in cell
- alter the energetic status of metabolites and promote their degradation
nomenclature of esters
- indicate the alkyl group of alcohol
2. carboxylate name of acid
hydrolysis of esters
scission of bond via water-mediated nucleophilic attack
- catalysed by acid or bases
- requires a polarised scission bond
what are tryacylglycerides (triglycerides, TAGs)?
esters between a triol (glycerlo, 1,2,3 trihydroxypropane and three organic acids with lenghts between 4-24
what are phospholipids?
glycerol, esterified at two positions with organic acids and at the third phosphoric acid
