Electrophilic addition selectivity, bromination, epoxidation, dihydroxylation and sp centres Flashcards
what is the difference between transition states and intermediate
TS: local maximum/ saddle point
Intermediate: local minimum - can be isolated
Explain the difference between c-c and c=c
c=c shorter and stronger as sp2 has more s character compared to sp3
What conditions to react water with an alkene, what product formed?
H2SO4 present, forms alcohol.
When under dilute conditions why does bisulphate anion not react?
H2SO4 in equilibrium with water, water stronger base than HSO4-, hence better nucleophile. When conc eq causes H3O+ to be present,
How do reduce alkyl hydrogen sulphate to alcohol
add water at room temp creating alcohol
Define regioselective and regiospecific
Regioselective: One possible product formed in larger amounts than other products
regiospecific: Mechanism can only form one product
what is sigma conjugation in cations
Neighbouring C-H sigma bongs overlap with empty p orbital resulting in overall stabilisation.
sigma orbital feeds extra electron density into empty p orbital. the more sigma bonds the more stable.
Order stabilities of carbocations
T > S > P
How do sigma conjugations occur in Radicals, conformations and anions
Radicals: sigma bond and SOMO
Conformations: Sigma bond and Sigma* orbital of antiperiplanar C-H bonds
Anions: no stabilisations possible
How many transitions states and intermediates during electrophilic addition
Two TS
One intermediate
Energy diagram has two saddle points with one minimum between
Which orientation can sp2 centre be attacked
sp2 is planar, attacked from top or bottom, no energetic preference for top or bottom.
How does bromine test for alkene
Red Br goes colourless in presence of alkene.
Why does only trans product form on Br2 reacting with planar C centre?
Bromonium ion forms during mechanism, lone pair on Br attacks back onto alkene.
Describe Bromination of alkene in terms of orbitals
Alkene pi orbital attacks sigma* on Br2 , Br-Br bond broken, bromonium ion formed. Bromide ion n orbital attacks C-Br Sigma* opening C-Br bond, dibromide product formed. backside attacks
How does nucleophilic attack occur on unsymmetrical alkenes?
Nucleophile attacks most substituted end of bromonium ion, more carbocation character.
