Organic Chem
ChemActivity 10: Exercises 1. Draw a complete mechanism including the intermediate and most likely product for the reaction of each alkene below with H-X.
H
+
H
Cl
+ Cl
Cl
+
+ Br
H Br H I Br
+
H
I H
+ I
H
2. Draw a complete mechanism of each pair of reactant including any favorable rearrangements and all important resonance structures of all intermediates.
Reactant Pair 1
Cl
H
Br
1 + Cl No shift stable benzylic carbocation
H: shift
H H Br
2 3
Cl
+ Cl
a. Which reaction has a lower PE carbocation intermediate? Reaction pair 1 is more stable (stabilized by resonance) 2o benzylic is more stable than 3o. b. Draw an energy diagram showing the reaction profiles of both reactions in the previous question. Use a dotted line for the first pair of reactants and a solid line for the second pair of reactants. (Assume the energy of the starting materials and products are the same for both pairs and the reactions are neither uphill nor downhill on net.)
2 1
3
c. Mark points on the energy diagram corresponding to each carbocation in your mechanisms. See the blue # above.
Reactants Products
1
3. Use a curved bouncing arrow to depict the hydride shift that will likely occur for each carbocation below, and explain why the new carbocation is lower in potential energy than the original. (Draw any important resonance structures of each!)
H H3C C H3C H H H C C H H3C H3C C H H H H C C H
2o
H H C H H C C H H H C C H H
3o carbocation - more stable
H C C H o H H C C H H C H H H C H
H C C
H H C C H H o H
2o
H
H
2 allylic carbocation more stable, the
1 allylic is delocalized over two carbons
4. Use a curved bouncing arrow to depict the alkyl shift that will likely occur for each carbocation below, and explain why the new carbocation is lower in potential energy than the original.
H H3C C H3C CH3 H H C C H H3C C CH3 H3C H C CH3
2o
H H C H H3C C C CH3 H H C C H H H
H
+
H
Cl
+ Cl
Cl
+
+ Br
H Br H I Br
+
H
I H
+ I
H
2. Draw a complete mechanism of each pair of reactant including any favorable rearrangements and all important resonance structures of all intermediates.
Reactant Pair 1
Cl
H
Br
1 + Cl No shift stable benzylic carbocation
H: shift
H H Br
2 3
Cl
+ Cl
a. Which reaction has a lower PE carbocation intermediate? Reaction pair 1 is more stable (stabilized by resonance) 2o benzylic is more stable than 3o. b. Draw an energy diagram showing the reaction profiles of both reactions in the previous question. Use a dotted line for the first pair of reactants and a solid line for the second pair of reactants. (Assume the energy of the starting materials and products are the same for both pairs and the reactions are neither uphill nor downhill on net.)
2 1
3
c. Mark points on the energy diagram corresponding to each carbocation in your mechanisms. See the blue # above.
Reactants Products
1
3. Use a curved bouncing arrow to depict the hydride shift that will likely occur for each carbocation below, and explain why the new carbocation is lower in potential energy than the original. (Draw any important resonance structures of each!)
H H3C C H3C H H H C C H H3C H3C C H H H H C C H
2o
H H C H H C C H H H C C H H
3o carbocation - more stable
H C C H o H H C C H H C H H H C H
H C C
H H C C H H o H
2o
H
H
2 allylic carbocation more stable, the
1 allylic is delocalized over two carbons
4. Use a curved bouncing arrow to depict the alkyl shift that will likely occur for each carbocation below, and explain why the new carbocation is lower in potential energy than the original.
H H3C C H3C CH3 H H C C H H3C C CH3 H3C H C CH3
2o
H H C H H3C C C CH3 H H C C H H H