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Chapter 4
Reactions of Alkenes

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04-00-01CO
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.
Keywords
bromonium, ion, potential, map, cis-2-butene, bridged
04-00-08UN
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.
Keywords
electrostatic, potential, cations, tert-butyl, isopropyl, ethyl, methyl
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.
Keywords
carbocation, stabilization, hyperconjugation, methyl, cation, figure, 4.1
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.
Keywords
MO, diagram, stabilization, hyperconjugation, figure, 4.2
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).
Keywords
transition, state, energies, Hammond, postulate, early, late, endergonic, exergonic, reaction coordinate
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).
Keywords
cations, isobutyl, tert-butyl, methylpropene, carbocations, reaction coordinate, figure, 4.4
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.
Keywords
reaction coordinate, structure, transition, state, problem, 3
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.
Keywords
hydrogenation, catalytic, adsorbed, metal, surface, figure, 4.6

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