Carboxylic Acids and Derivatives Flashcards
Describe the structire of the carbon atom in a COOH group.
The C is sp2 hybridised and molecular geometry is trigonal planar with respect to carboxyl C.
Why does carboxylic acids have higher boiling points than their corresponding alkanes and alcohols of the similar Mr?
Carboxylic acids can form hydrogen bonds with each other. Carboxylic acids form stronger hydrogen bonds than alcohols because the -OH group is more polarised due to the presence of electron withdrawing carbonyl group. Carboxylic acid molecules dimerise in the vapour state and in non-polar solvents, forming two hydrogen bonds between each pair of molecules
The H aom is more electron decficient and has a greater +dipole in acid.
They exist as monomers or dissociate to some extent into H+ and RCO2- in polar solvents.
Why does the boiling points of carboxylic acids increase wiht inceasing relative molecular mass?
Boiling points increase iwth increasing relative molecular mass because this leads to an increase in the number of electrons the molecules have and thus lead to stronger id-id interactions between the molecules.
Why lower aliphatic acids completely miscible with water?
This is because the -COOH group is able to form hydrogen bonds with water molecules.
Why are higher aliphatic acids not miscible with water?
As the hydrocarbon chain lengthens, the pd-pd interactions between the larger non-polar alkyl group and water molecules do not release sufficient energy to overcome the strong hydrogen bonds between the water molecules. In addition, the larger alkyl group also hinders the formation of hydrogen bonds between the carboxylic acid functional group and water molecules.
How do you prepare carboxylic acids from alcohols and aldehydes?
Carboxylic acids an be prepared by oxidation of primary alcohols and aldehydes.
Reagents and conditions:
KMnO4(aq), H2SO4(aq), heat OR K2Cr2O7(aq), H2SO4(aq), heat
Observation:
puple KMnO4 turns colourless OR orange K2r2O7 turns green
How do you prepare carboxylic acids from alkenes?
Carboxylic acids an be prepared by oxidative cleavage of alkenes
Reagents and conditions:
KMnO4(aq), H2SO4(aq), heat
Observation:
puple KMnO4 decolourises
K2Cr2O7 cannot be used as it is a weaker oxidising agent
How do you prepare carboxylic acids from alkylbenzene?
Carboxylic acids an be prepared by side-chain oxidation of an alkylbenzene to form bezoic acid.
Reagents and conditions:
KMnO4(aq), H2SO4(aq), heat
Observation:
puple KMnO4 decolourises.
K2Cr2O7 CANNOT be used
