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
what are phosphorylated amino acids?
three amino acids have hydroxyl groups where esterification can take place (serine, theorinine, tyrosine)
