Acidity & Electrophiles Flashcards
(14 cards)
What is an acid?
Proton donor
What is a conjugate base?
Proton acceptor
Equation for pKa
PKa = -log10Ka
Equation for Ka
Ka = [H+] [A-]
—————
[HA]
Ions and their pH
Ammonium ion (positively charged) = pH 1
Zwitter ion (exists with both charges) = pH 7.4
Carboxylate ion (negatively charged) = pH 13
What is the isoelectric point pl ?
The pH when there is no net charge
This is always 6.02
What affects stability in acidity?
Molecules containing more electronegative ions are more stable
E.g. a molecule containing oxygen is more stable than one containing Nitrogen or carbon
Factors to consider in acidity
- Bond strength (how readily it dissociates)
- Solvation (in water = pKa)
- Charge of stabilisation (of the anion or cation)
What affects reactivity in acidity?
Molecules with more electronegative ions are less reactive
Compare the pKa in Serine and Aspartic acid
Serine has pKa of ~16/17
Aspartic acid has pKa of ~5 as its side chain is more acidic = more resonance possible as ions can be delocalised
What are electrophiles?
Atoms that are electron deficient and have a positive/partial positive charge
Types of these include
- Cations
- Protons
- Metal cations
- Molecules with electronegative atoms = partial positive/negative charges
Stability of carbocations
Stability increases from primary to tertiary
How can electrophiles be stabilised through resonance?
With a neighbouring phenyl ring
Biologically relevant electrophiles
Alkylating reagents
- sulfur mustard
- amine mustards
- used as chemical weapons and chemotherapeutics
- carbon near Cl is highly electrophilic
Phosphorylated adducts
- Ribose-5-diphosphate
- a key DNA building block
- phosphate group is a good leaving group
Covalent drug inhibitors
- Nirmatrelvir
- a COVID 19 anti-viral
- nitrile ‘warhead’ (one with a triple bond) reacts with RSH residues
