Advices For Studying Organic Chemistry

1) The p orbital of this new sp^2 -hybridized carbon atom overlaps with the p orbital

of the central carbon atom ⇒ in the allyl radical three p orbitals overlap to form

a set of π MOs that encompass all three carbon atoms.

2) The new p orbital of the allyl radical is conjugated with those of the double

bond ⇒ the allyl radical is a conjugated unsaturated system.

1 C C

H

H

H

HH

(^23)
sp^3 Hybridized
X
δ X
C
1 C C
H
H
H
H H
C (^231) C C
H
H
H
δ C 23 H
++ sp (^2) Hybridized
3) The unpaired electron of the allyl radical and the two electrons of the π bond are
delocalized over all three carbon atoms.
i) This delocalization of the unpaired electron accounts for the greater stability of
the allyl radical when compared to 1°, 2°, and 3° radicals.
ii) Although some delocalization occurs in 1°, 2°, and 3° radicals, delocalization is
not as effective because it occurs through σ bonds.
6-11- 02

2. Formation of three π MOs of the allyl radical:
   
   
   1. The bonding π MO is of lowest energy ⇒ it encompasses all three carbon atoms
      and is occupied by two spin-paired electrons.
      i) The bonding π orbital is the result of having p orbitals with lobes of the same
      sign overlap between adjacent carbon atoms ⇒ increases the π electron density
      in the regions between the atoms.
   
   
   2. The nonbonding π orbital is occupied by one unpaired electron, and it has a node
      at the central carbon atom ⇒ the unpaired electron is located in the vicinity of
      carbon 1 and 3 only.
   
   
   3. The antibonding π MO results when orbital lobes of opposite sign overlap
      between adjacent carbon atoms ⇒ there is a node between each pair of carbon
      atoms.