Lecture 4 Flashcards
bond angles vary with?
size of substituent
what does a higher electronegativity on the oxygen atom mean?
the lone pair of electrons on the oxygen atom is less likely to be protonated than those on the nitrogen atom.
bonding molecular orbitals and antibonding molecular orbitals.
- bonding molecular orbitals = less energy than parent molecular orbitals
- antibonding molecular orbitals = more energy than parent molecular orbitals.
atomic orbitals combine most effectively to molecular orbitals if…
they have similar shape and energy
bond order equation
bond order = (electrons in bonding MO - electrons in antibonding MO)/2
molecular oxygen in increasing energy
ground state triplet, ground state singlet, excited state singlet
multiplicity of energy levels equation
M = 2S + 1
S = sum of spin values in highest occupied molecular orbital (HOMO)
what does the molecular orbital theory predict about oxygen?
molecular oxygen is a diradical
- a molecular species with 2 electrons occupying 2 degenerate molecular orbitals.
what does the loss of an alcohol function mean?
it does not negate biological activity
what does the loss of an amino group mean?
results in loss of biological activity
what are alcohols with 2 or 3 hydroxyl groups known as ?
diols (glycols) or triols
what are hydrocarbons with more than 3 hydroxyl groups knows as?
polyols (e.g carbohydrates)
why are phenols much stronger acids than alcohols?
due to delocalisation of the negative charge on the conjugate base (phenoxide ion)
what properties does a more acidic phenol have?
good antibacterial properties
(e.g. triclosan, which is added to toothpaste and household detergents due to its antibacterial action.)
phenols are…
special alcohols and antioxidants
homolytic and heterolytic
- homolytic = oxidation
- heterolytic = ionisation
what happens when the phenoxy radical preferentially tends to dimerse?
it terminates the radical chain reaction
ethers properties
- much less polar than parent alcohols
- formerly used in anaesthesia (diethyl ether) before non-flammable homologues were discovered to have similar biological activity (haloethane) by reacting with nerve cell membranes.
- ethers are liable to have potentially explosive epoxides in presence of molecular oxygen and UV light.
cyclic ethers are known as…
epoxides
why are 3 membered ring epoxides highly reactive?
because of torsional strain.
what are commonly found in the structure of drug molecules?
ketones
why are aldehydes less commonly found in the structure of drug molecules?
because of their higher reactivity towards nucleophiles
how are aldehydes found?
in the open chain form of reducing sugars
what does the high reactivity of aldehydes result in?
general cytotoxicity
what is the acidity of carboxylic acids due to?
the efficient resonance delocalisation - of the negative charge - of the carboxylate ions.
what affects the acidity of carboxylic acids?
electronic effects (inductive and resonance)
EWG AND EDG on acidity
- EWG increase acidity by charge delocalisation
- EDG decrease acidity by charge localisation
how does h-bonding affect acidity in salicylic acid?
intramolecular h-bonding contributes to the charge delocalisation of the conjugate base.
intramolecular h-bonding is not possible in aspirin
what increases the aqueous solubility of drugs with carboxylic funtions?
formation of salts with alkali
what is the aqueous solubility of drugs limited by?
size and lipophilicity of carboxylate ion.
sulfur compared to oxygen
- sulfur belongs to oxygen periodic group
- shares some properties of oxygen
- larger atomic radius
- lower electronegativity
- empty 3d orbitals avaliable for bonding.
a larger sulfur atom is what?
better at delocalising charge than oxygen.
hence thiols (S-H) are more acidic than alcohols
thiols on heavy metals
- large binding affinity for heavy metals
- therefore used to treat heavy metal poisoning by forming water soluble complexes which can be excreted
what are thiols responsible for
- forming -S-S - bridges by crystalline residues
- detoxifying properties of glutathione (GSH)
