Functional groups with acidic behaviour Flashcards
1
Q
What are ionic bonds?
A
occurs due to the electrostatic interaction between two charged species (cation and anion)
2
Q
What are acidic functional groups and their properties (5)
A
- species (groups) that can donate protons
- Strong acids have an equilibrium that lies to the right (products) and has large Ka and small pKa.
- Weak acids have an equilibrium that lies to the left (reactants) and have small Ka and large pKa.
- Ka = [A-][H+]/[HA]
- pKa = -logKa
3
Q
What are carboxylic acids and their properties (7)
A
- consists of a carbonyl group and a hydroxyl group (COOH), as a consequence, it promotes strong intermolecular interactions
- R can be aromatic or aliphatic.
- =O and O act as H bond acceptors
- H acts as an H bond donor.
- The group is planar, containing sigma and pi bonds and sp2 hybridisation.
- The anion carboxylate is stabilised by resonance.
- aliphatic carboxylic acids have pKa values of 4-5
4
Q
What is the nature of ‘’R’’ and acidity (3)
A
- the value of pKa varies considerably as a function of the nature of R
- EWG stabilise the negative charge, therefore stabilising the carboxylate, increasing the acidity (lower pKa)
- EDG do not stabilise the negative charge, therefore, destabilises the carboxylate, decreasing the acidity (higher pKa)
5
Q
What are phenols and their properties (6)
A
- Phenols consist of a benzene ring bonded to an OH group.
- O acts as an H bond acceptor and H as an H bond donor.
- Phenols are more acidic than alcohols because the negative is stabilised by resonance (delocalised on the aromatic ring)
- EWG increase the acidity of the phenol because it favours the delocalisation of the charge on the ring
- EDG decrease the acidity of the phenol because it disfavours the delocalisation of the charge on the ring
- CYP450-mediated oxidation of phenol leads to the formation of 1,2 and 1,4-dihydroxybenzene, which are easily oxidised to ortho-quinone and para-quinone (redox toxicity). The hydroxylation of the ring occurs via an epoxide intermediate (toxic electrophile)
6
Q
What are the properties of sulfonamides (2)
A
- R can be aliphatic or aromatic.
- The proton on the sulphonamide group is acidic because of the EWG effect of the sulphonic group and because the anion resulting from the deprotonation is stabilised by resonance.
7
Q
What are the properties of sulfonylureas (2)
A
- R and R1 can be aliphatic or aromatic
- have a similar stabilisation as the one for sulfonamides (acidic because of the EWG effect of the sulfonic group and because the anion resulting from the deprotonation is stabilised by resonance)
8
Q
What are the properties of sulfates and phosphates (4)
A
- Sulfonic acids are very strong acids, which deprotonate in aqueous environment
- pKa = 0-2
- The anion is stabilised by resonance: the charge is delocalised on the sulfonic group
- similarly, phosphonic acids are very strong acids (pKa1 = 1.5, pKa2 = 6.5)