1. Figure Number: CO
Title: Bromonium Ion
Caption: Potential map of the intermediate generated in the reaction of cis-2-butene with elemental bromine.
Notes: The bromonium ion is a bridged structure in which a bromine atom is simultaneously bonded to two carbon atoms with half of a bond formed with each. Each carbon bears half of a positive charge.

2. Figure Number: UN
Title: Electrostatic Potential Maps
Caption: Electrostatic potential maps for the tert-butyl, isopropyl, ethyl, and methyl cations.
Notes: The color blue indicates the areas with the most positive electrostatic potential. The green color indicates areas with less positive electrostatic potential. The more green present, the more stable the compound.

3. Figure Number: 04-01
Title: Figure 4.1
Caption: Stabilization of a carbocation by hyperconjugation: the s electrons in the adjacent bond spread into the empty p orbital. Hyperconjugation cannot occur in a methyl cation.
Notes: The positive charge on a carbon signifies an empty p orbital. The sigma orbital of an adjacent bond can overlap with the empty p orbital. This allows the positive charge to be spread out over the molecule and not localized on one atom.

4. Figure Number: 04-02
Title: Figure 4.2
Caption: MO diagram showing stabilization by hyperconjugation.
Notes: The combination of an empty p orbital with a sigma bond yields a bonding orbital which has some of the character of the original sigma bond and some of the character of a pi bond between adjacent carbons. The electrons in this bonding orbital are spread out, as is the positive charge of the carbocation, as shown in Fig. 4.1.

5. Figure Number: 04-03
Title: Hammond Postulate Reaction Coordinate Diagrams
Caption: Curve (I) indicates an early transition state, (II) indicates a midway transition state, and (III) a late transition state.
Notes: In an exergonic reaction (I), the transition state is energetically closer to the reactant (early). In an endergonic reaction (III), the transition state is energetically closer to the product (late).

6. Figure Number: 04-04
Title: Figure 4.4
Caption: Reaction coordinate diagram for the addition of H+ to 2-methylpropene to form the primary isobutyl cation and the tertiary tert-butyl cation.
Notes: Methylpropene reacts with H+, which can result in two carbocations, the primary isobutyl cation and the tertiary tert-butyl cation. The tertiary cation is more stable (has lower free energy).

7. Figure Number: 04-04-02UNa-d
Title: Problem 3
Caption: Four reaction coordinate diagrams.
Notes: For each of the reaction coordinate diagrams, determine whether the structure of the transition state will more closely resemble the structure of the reactants or the structure of the products.

8. Figure Number: 04-06
Title: Figure 4.6
Caption: Hydrogen is adsorbed on the surface of the metal, and the alkene complexes with the metal by overlapping orbitals.
Notes: Breaking the pi bond of the alkene and the sigma bond of the H2 and forming the C-H sigma bonds all occur on the surface of the metal. The alkane product diffuses away from the metal surface as it is formed.