Pharmacology Flashcards
Define Co-ordinate bonding
a form of covalent bonding where one atom supplies both shared electrons to the bond.
e.g. Ocygen in H2O and Nitrogen in NH3
What structural cause results in desflurane being more slowly metabolised than isoflurane?
Desfluranes Fluourine is more electronegative than chlorine in isoflurane.
This makes the C-F bone more polarised than the C-Cl bond making it more ionic in character and stronger than the C-Cl bond.
When does polarization occur ?
When the cation (+ve) distorts the electron cloud of an anion (-ve). causes more electron charge between the two nuclei, thus producing a degree of covalent bonding.
Name the 3 types of intermolecular attraction
- Van Der waals forces: Weakest force. electrons in the outer shell may form an instantaneous dipole inducing an instantaneous dipole in a neighbouring atom.
- Dipole-Dipole attraction: Attraction between polar molecules.
- Hydrogen bonding
Type of dipole-dipole. Strongest. Occurs when hydrogen is bound to a very electrongative atom e.g. oxygen or fluorine. Creates a strongly electronegative atom that then forms dipole-dipole attractions.
How can covalent bonds be broken ?
- Homolytic fission -> each element takes an electron to form a free radical.
- Heterolytic fission- One element takes all the electrons and two oppositely charge ions are formed.
Define a strong electrolyte
dissociate completely in an aqueous solution to form separate ions e.g. NaCl -> Na+ and Cl-. Very water soluble but poorly lipid soluble.
Define a weak electrolyte
Only some molecules dissociate completely in aqeous solution.
Ionisaztion may be pH dependant.
Which two functional groups are most important in allowing small organic molecules to act as weak electrolytes?
Carboxyl COOH and Amine NH2 groups
What is pKa
pKa is the pH at which the concentration of the proton donor form is equal to that of the proton acceptor form.
How do you derive pKa?
R-COOH ⇔ R-COO- + H+
as an example.
Proton donor (k1) ⇔ Proton acceptor (k2) + H+
At equilibrium K1 = K2
Rearrange
H+ = K1/K2
K1/K2 is the dissociation constant
Negative logarithim of K1/k2 = pKa
i.e. the pH at which the proton acceptor concentration is equal to the proton donator form.
K1/K2 = 1 at equilibrium
What is pH
The pH is equal to −log10 c, where c is the hydrogen ion concentration in moles per litre.
When are weak acids and bases ionised?
Weak acids are ionised above their pKa
Weak bases are ionised below their pKa
What is the pKa of thiopentol ?
Is it a weak acid or base?
pKa 7.6
Weak Acid
What is the pKa of propofol and is it acid or base?
pKa 11.0
Weak acid
What is the pKa of etomidate and is it acid or base?
pKa 4.2
Weak Base
