FMO and WH rules

Question 1

Fundamentals of frontier orbital theory

Answer 1

Reaction occurs via the interaction of a HOMO and LUMO of the correct symmetry and energy

Question 2

Orbital rules

Answer 2

Same number of atomic and molecular orbitals, increasing number of nodes per MO from 0

Question 3

Suprafacial vs antarafacial reactions

Answer 3

Supra means both bonds form on the same side of the reactant, antara means they form on opposite sides

Question 4

What does a thermally allowed reaction mean in terms of the frontier orbitals

Answer 4

The ground state frontier orbitals are of the correct energy and phase to allow for reaction to occur

Question 5

What does photochemically allowed mean with reference to frontier orbitals

Answer 5

The promotion of a single electron to generate a ‘pseudo HOMO’ allows for in phase interactions between the HOMO and LUMO

Question 6

Effect of substituents on the energies of the HOMO and LUMO

Answer 6

alkyl and phenyl species narrow the gap between the bonding and anti-bonding orbitals. EWG lower the energy of the system, EDG increase the energy of the system

Question 7

What are the Woodward-Hoffmann rules

Answer 7

(4q+2)s + 4r(a) components must be
thermal = odd
photochemical = even
where r and q are integers

Question 8

What does a and s stand for the in WH rules?

Answer 8

antarafacial and suprafacial