PYRAMIDAL MEHTYL

Walsh Diagram: Pyramidal Methyl

• Can predict how geometric distortions will
affect the MO’s of a fragment (planar CH3).
• Make the orbitals of the pyramidal methyl
group by distorting the planar methyl system
and following Rule 4.
• Rule 4: Start constructing MO’s for structures with
high symmetry, then produce MO’s for related but less
symmetric structures through systematic distortions of
orbitals for higher symmetry.
• Diagram that follows orbital energies as a
function of angular distortions is called a
Walsh diagram. (example to the left)
• Noted changes:
• Energy of A does not change much

• Energy of B and C is raised more than A is
lowered due to their directionality.
• Distortion results in favorable overlap
between H’s and C 2pz lowering energy of D,
resulting in it becoming significantly bonding.
• Rule 7... is then applied: (If the two highest energy MO’s of a given symmetry derive primarily from different
kinds of atomic orbitals, then mix the two MO’s to form hybrid orbitals).
• MO’s D and E have similar symmetry but are based on 28 C 2p and C 2s respectively.
• Group orbitals for methyl: σ(CH3) w/ σ symmetry,
• π(CH3) (a degenerate pair of orbitals) w/ π symmetry.

• σ(out) w/ σ symmetry, pointed away from the hydrogens