CARBOXYLIC ACID Flashcards
Why cant RCOOH dimerise in H2O
RCOOH will form H-bonds with H2O molecules instead of itself
Why can RCOOH dimerise in CCl4(g)
RCOOH cannot form H-bonds with non polar or organic solvents, thus it is able to dimerise, the MR of RCOOH is twice its original Mr
List all synthesis of RCOOH
Oxidation
1) Vig [O] of alkene
2) Vig [O] of aldehyde/primary alc
Acidic Hydrolysis of:
Nitriles, Esters, Amides
Hydrolysis of Acyl Chloride(no need acidic medium)
List synthesis of Acyl Chloride
Nu Sub of RCOOH
Why do RCOOH have higher BP than ROH with similar Mr
Presence of e-withdrawing C=O group results in more polar O-H bond compared to O-H bond in ROH. More energy is required to overcome the stronger intermolecular H-bonds b/w RCOOH molecules
Why does solubility of RCOOH decrease as number of carbons increases
As the alkyl groups become larger, the idid interactions b/w alkyl grps become predominant and non-polar chains interfere with the H-bonding b/w the C=O and -OH groups with the water molecules
Explain the acidity of RCOOH compared to phenol and ROH
RCOOH most acidic as carboxylate anions(RCOO-) are stabilised by the delocalisation of negative charge over two highly electronegative oxygen atoms, decreasing the charge density on the O atom and stabilises the carboxylate anion.
More stable than phenoxide:
-ve charge is deloc and equally distributed over the C atom and 2 highly EN O atoms. In phenol, -ve charge density is only slightly decreased over the 6 C atoms that have lower EN than O atom, RCOO- anion is more stable than phenoxide ion, thus RCOOH more acidic than phenols
Identify the RA that can reduce RCOOH(LiAlH4, H2 w/ Ni Cat, NaBH4)
LiAlH4
Compare BP of RCOCl and RCOOH
RCOCl does not have -OH group, thus unable to form intermolecular H-bonds, hence less amt of energy is req to overcome the weak pdpd int b/w acyl chloride molecules
Compare ease of hydrolysis/reagants and conditions b/w C6H5Cl, RCl, RCOCl
C6H5Cl: NaOH, heat at high temp and pressure
->relatively stronger sp2 C-Cl bond due to overlapping of Cl p-orbital with pi e-cloud of BZ ring, C-Cl bond has partial double bond character
RCl: NaOH, HUR
->Relatively larger δ+ charge on e-def carbon as it is bonded to EN atom Cl, which attracts Nu strongly and facilitates the breaking of C-Cl bond for hydrolysis to happen
ROCl: H2O, rtp
-> largest δ+ charge as it is bonded to 2 EN atoms O and Cl , thus attracting Nu most strongly, and C-Cl bond breaks most readily, therefore no heating required
all RCOOH cannot be oxidised except
Methanoic acid, ethanedioc acid
why is RCOCl most reactive compared to RCOOH, RCOOR, RCONH2
RCOCl contains an e-withdrawing Cl group via inductive effect whereas the -OH, -OR, -NH2 substituents are e-donating via resonance effect. The C atom in RCOCl is the most e- deficient therefore it is the most susceptible to Nu sub hence it is the most reactive
When will dimerisation of RCOOH take place
In liquid state of organic solvents(eg benzene, CCL4, ) or vapour/gas state
Why is H2SO4 required in condensation reaction b/w RCOOH and ROH
H2SO4 acts as a dehydrating agent which increases the yield of ester as the POE shifts right. H2SO4 also acts as catalyst to speed up rxn
Why is condensation reaction between RCOOH and ROH reversible
RCOOH is an acid while ROH is a weak acid
Why RCOOH and RNH2 cannot undergo condensation
RCOOH is an acid while RNH2 is a base, therefore they will undergo acid base reaction instead of condensation
