C3 Ionisable functional groups Flashcards
state some examples of ionisable drugs
- all oral drugs for migraines (all contain either carboxylic acid, amine or phenol)
why is a phenol ionisable?
it is a weak acid
what is the formula for pH?
-log[H+]
what kind of scale is pH?
logarithmic
eg. a solution with pH 2 is 10 times more acidic than/ has 10 times more proton concentration than a solution with pH 3
describe strong acids giving an example and equation for dissociation
- fully dissociate
- eg. HCl
HCl –> H+ + Cl-
HCl –> H+ + Cl-
in this dissociation equation for hydrochloric acid, what is Cl- known as?
conjugate base (can act as a base by accepting a proton)
describe weak acids giving an example and equation for dissociation
- partially dissociate (form equilibrium)
- eg. ethanoic acid (CH3COOH)
CH3COOH ⇌ H+ + CH3COO-
(equilibrium arrow required)
CH3COOH ⇌ H+ + CH3COO-
in this dissociation equation for hydrochloric acid, what is CH3COO- known as?
conjugate base (it is able to act as a base by accepting a proton)
what is Ka? what do its different values indicate?
- acid dissociation constant
- high = greater dissociation / stronger acid
- low = less dissociation / weaker acid
what is the formula for Ka?
definition and example of acids
- acids are capable of donating a proton (H+)
- eg. carboxylic acid, phenol (weaker but still an acid)
definition and example of bases
- bases are capable of accepting a proton
- eg. amine, aniline (weaker but still a base)
structure of aniline
what are the general equilibrium equations for forming conjugate acids and bases from standard acids and bases?
what do you get if a base accepts a proton?
its conjugate acid
what do you get if an acid loses a proton?
its conjugate base
what is a limitation of logP that means we need logD instead?
- logP can only be applied to the uncharged form of molecules
- ionisation makes a big difference to lipophilicity
- partition coefficient (D) is needed
in a carboxylic acid, logP and logD have different values, logD is lower. why is this and what do these values indicate?
- logP is of the carboxylic acid
- logD is of the carboxylate
- logD being lower means the carboxylate is less lipophilic than the carboxylic acid and more polar
what are the 2 variations of the formula for pKa?
what does a low pKa indicate?
greater dissociation
stronger acid
what does a high pKa indicate?
less dissociation
weaker acid
what is pKa?
the pH at which the group is 50% ionised and 50% unionised
what is the case if the pH is below the pKa of the ionisable group? does this mean the molecule will be charged?
- the group will be protonated
- if it is a protonated acid (HA) then neutral
- if it is a protonated base (HA+) then it is charged
for an ACID, what is the case for the acid group if the pH is below the pKa?
more than 50% protonated
