electrophilic addition selectivity

Question 1

what is the orbital structure of an sp2 centre eg on ethene

Answer 1

Trigonal planar - 3 sp2 hybrids and one unused p orbital which is orthogonal to hybrids
orthogonal P orbitals on separate C overlap forming pi bond. sp2 orbitals on C overlap with 1s on H atoms and with each other forming sigma frame.

Question 2

compare sp3 and sp2 bonds

Answer 2

sp2 bonds have more S character so have shorter and stronger bonds

Question 3

compare electrophilic addition and elimination

Answer 3

electrophilic addition to alkene is reversible as the backward reaction is E1

Question 4

how does dilute H2SO4 react in electrophilic addition

Answer 4

Double bond attacks proton on H3O+, LP on H2O bonds to carbocation, another H2O attacks H on H2O bonded to alkane leaving alcohol and H3O+ is regenerated

Question 5

why does bisulphate react in with dilute H2SO4

Answer 5

Bisulphate is in equilibrium with water where water is a stronger base than HSO4- , H2O better nucleophile and so more likely to attack on carbocation.
When conc only 2-4% water eq position means most water is H3O+ so no water available to attack ,

Question 6

use Markovnikov’s rule to predict major product when HX reacts with double bond

Answer 6

H atom will bond to C atom with the most hydrogens

Question 7

define regioselective

define regiospecific

Answer 7

one possible product is formed in larger amounts than the other one(s)

the mechanism can only form one product

Question 8

how does sigms conjugation stabilise the sp2 centres

Answer 8

with correct orientation and phase for overlap C-H sigma bond feeds extra electron density into empty p orbital.
when carbocation involved the most highly substituted is favoured

Question 9

describe the sigma conjugation in cations, radicals, conformations, anions

Answer 9

cations: Sigma bond and empty p orbital
radical: SOMO and sigma bond

Conformations: Sigma and sigma* orbitals of anti-periplanar C-H bonds

Anions: no stabilisation