Which of the following is the most stable radical

1
Which of the following is the most stable
radical
2
Rank the following alkyl radicals in order of
increasing stability (least lt lt ltmost).
1lt3lt2lt4
3
What is the product of the following reaction
4
Predict the product of the following
reaction.1-methylcyclohexene HBr/H2O2
5
Identify the reagent(s) that will promote the
following transformation.

• HBr tetrahydrofuran
• HBr peroxides
• Br2 CCl4
• Br2 H2O

6

• Conjugation occurs whenever p orbitals can
  overlap on three or more adjacent atoms.

• The four p orbitals on adjacent atoms make a
  13-diene a conjugated system.

7

• Having three or more p orbitals on adjacent atoms
  allows p orbitals to overlap and electrons to
  delocalize.

• 14-Pentadiene is an isolated diene.
• The bonds in 14-pentadiene are too far apart
  to be conjugated.

8
Which of these compounds have delocalized
electron density


9

• The allyl carbocation is another example of a
  conjugated system.

• Conjugation stabilizes the allyl carbocation.

10

• Drawing resonance structures for the allyl
  carbocation is a way to see how to use Lewis
  structures to illustrate how conjugation
  delocalizes electrons.

• The true allyl cation is a hybrid of the two
  resonance forms.
• In the hybrid the positive charge is delocalized
  over the two terminal carbons.
• Delocalizing electron density lowers the energy
  of the hybrid thus stabilizing the allyl
  carbocation and making it more stable than a
  normal 1 carbocation.

11
What are the resonance structures of these
compounds
12

• Experimental data show that the stability of the
  allyl cation is comparable to a more highly
  substituted 2 carbocation.

13
Common Examples of Resonance 1. The Three Atom
Allyl System XY-Z
Examples are the allyl cation and the acetate
anion. The two resonance structures differ in the
location of the double bond and either the
charge the radical or the lone pair
generalized by .
14

• 2. Conjugated Double Bonds
• Cyclic completely conjugated rings like benzene
  have two resonance structures drawn by moving
  the electrons in a cyclic manner around the ring.
• Three resonance structures can be drawn for other
  conjugated dienes two of which involve
  separation of charge.

15
3. Cations Having a Positive Charge Adjacent to a
Lone Pair
The overall charge is the same in both resonance
structures. Based on formal charge a neutral X
in one structure must bear a () charge in the
other.
16
4. Double Bonds Having One Atom More
Electronegative Than the Other
17
Draw the resonance structures
18
The resonance hybrid more closely resembles the
major contributor
19
Draw the other resonance structure and predict
which is more stable.
20
Draw the three resonance structures of CH3CO2H
and rank their stability.
1
3
2
21
Electron Delocalization Hybridization and
Geometry Consider the two Lewis structures (A and
B) for the resonance stabilized anion
(CH3COCH2).

• Based on structure A the indicated carbon is sp3
  hybridized with the lone pair of electrons in an
  sp3 hybrid orbital.
• Based on structure B however it is sp2
  hybridized with the unhybridized p orbital
  forming the portion of the double bond.

22

• The electron pair on the carbon atom adjacent to
  the CO can only be delocalized if it has a p
  orbital that can overlap with two other p
  orbitals on two adjacent atoms. Thus the
  terminal carbon atom is sp2 hybridized with
  trigonal planar geometry.
• Three adjacent p orbitals make the anion
  conjugated.

23
Determien the hybridization of the indicated
atoms.



All three are sp2 hybridized.
24

• Conjugated Dienes
• Conjugated dienes are compounds having two double
  bonds joined by one bond.
• Conjugated dienes are also called 13-dienes.
• 13-Butadiene (CH2CH-CHCH2) is the simplest
  conjugated diene.
• Three stereoisomers are possible for 13-dienes
  with alkyl groups bonded to each end carbon of
  the diene.

25

• Two possible conformations result from rotation
  around the CC bond that joins the two double
  bonds.

• Note that stereoisomers are discrete molecules
  whereas conformations interconvert.

26
Draw the three possible stereoisomers of
24-octadiene. Pick which one is (2E4E)
24-octadiene.

27
Draw the s-cis and s-trans conformations of
(3Z5Z)-45-dimethyl -35-octadiene
s-trans
s-cis
28

• The CarbonCarbon Bond Length in 13-Butadiene
• Four features distinguish conjugated dienes from
  isolated dienes.
• The CC single bond joining the two double bonds
  is unusually short.
• Conjugated dienes are more stable than similar
  isolated dienes.
• Some reactions of conjugated dienes are different
  than reactions of isolated double bonds.
• Conjugated dienes absorb longer wavelengths of
  ultraviolet light.

29
The CarbonCarbon Bond Length in
13-Butadiene The observed bond distances can be
explained by looking at hybridization.
30

• A resonance argument can also be used to explain
  the shorter CC bond length in 13-butadiene.
• Based on resonance the central CC bond in
  13-butadiene is shorter because it has partial
  double bond character.

31

• Finally 13-butadiene is a conjugated molecule
  with four overlapping p orbitals on adjacent
  atoms.
• Consequently the electrons are not localized
  between the carbon atoms of the double bonds but
  rather delocalized over four atoms.
• This places more electron density between the
  central two carbon atoms of 13-butadiene than
  would normally be present.
• This shortens the bond.

32
Using hybridization compare the C-C bonds of the
following three compounds.
sp3 25 s character
sp2 33 s character
sp 50 s character
Using resonance why are the two CO bonds the
same length
The two resonance structures show how the
electron density is delocalized over 3 atoms.