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Chapter 11
Elimination Reactions of Alkyl Halides

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11-00CO
Title
Elimination Reaction
Caption
Electrostatic potential maps and structures of reactants and products of the elimination reaction undergone by methoxide and 3-chloropentane.
Notes
Elimination reactions occur when nucleophiles act as bases rather than nucleophiles. The nucleophile removes a proton on the carbon adjacent to the carbon containing the leaving group. The sigma bond between this adjacent carbon and the hydrogen becomes a pi bond between the adjacent carbon and the carbon bearing the leaving group, and the leaving group leaves. These steps, done in different orders in different circumstances, yield alkene products.
Keywords
electrostatic, potential, maps, methoxide, chloropentane, elimination
11-00-04.1UN
Title
E2 Reactivities
Caption
Relative reactivities of alkyl halides in E2 reactions.
Notes
Alkyl halides with better leaving groups react faster by E2 than do alkyl halides with poor (unstable) leaving groups.
Keywords
E2, reactivities, alkyl, halide, leaving, groups
11-01
Title
Figure 11.1
Caption
Reaction coordinate diagram for the E2 reaction of 2-bromobutane and methoxide ion.
Notes
Since the transition state is somewhat product-like, formation of the more stable internal alkene product involves a more stable transition state, less activation energy, and a faster relative rate.
Keywords
figure, 11.1, reaction coordinate, diagram, E2, 2-bromobutane, methoxide
11-01-05.1UN
Title
Products of E2 Reactions
Caption
Products of the reactions of hydroxide ion with 4-chloro-5-methyl-1-hexene and 2-bromo-3-methyl-1-phenylbutane.
Notes
E2 reactions usually yield predominantly the most stable alkene products, which in this case is the conjugated alkene products.
Keywords
products, E2, conjugated, alkene
11-01-07T01
Title
Table 11.1 Effect of steric properties on distribution of products in an E2 reaction
Caption
Notes
Keywords
11-01-09T02
Title
Table 11.2 More substituted product/ Less substituted product
Caption
Products obtained from the E2 reaction of methoxide and 2-halohexanes.
Notes
The reaction with fluoride leaving group yields the less stable terminal alkene product predominantly. With fluoride as the leaving group, the transition state resembles the carbanion obtained by removing hydrogen from a carbon adjacent to the carbon bearing the leaving group more than it (the transition state) resembles the product alkene. Since a primary (terminal) carbanion is more stable than a secondary (internal) carbanion, this reaction yields mostly terminal olefin. The hydrogen is abstracted from the terminal carbon in preference to the internal carbon.
Keywords
table, 11.2, E2, methoxide, 2-halohexanes
11-01-25.1UN
Title
Hyperconjugation
Caption
Orbital picture of a carbocation stabilized by hyperconjugation.
Notes
Hyperconjugation makes a hydrogen attached to a carbon adjacent to a carbocation more acidic.
Keywords
hyperconjugation, orbital, carbocation, acidic, hydrogen
11-02
Title
Figure 11.2
Caption
Reaction coordinate diagram for the E1 reaction of 2-chloro-2-methylbutane with base.
Notes
The major product is the more stable alkene, because both products come from a common intermediate and the relative stabilities of the transition states leading to products from the common intermediate determine which product forms faster, even though these transition states occur after the rate-determining step. The second transition state in the reaction path has a small amount of product character, so the transition state leading to the more stable product is slightly more stable.
Keywords
figure, 11.2, reaction coordinate, diagram, E1, 2-chloro-2-methylbutane
11-02-01UN
Title
Alkyl Effect on E1 Reactivities
Caption
Relative reactivities of alkyl halides in an E1 reaction.
Notes
Relative reactivities of alkyl halides in E1 reactions parallels the stabilities of the corresponding alkyl cations.
Keywords
E1, reactivity, alkyl, halides, cations, stabilities
11-02-01.1UN
Title
Leaving Group Effect on E1 Reactivities
Caption
Relative reactivities of alkyl halides in an E1 reaction.
Notes
Relative reactivities parallel leaving-group (halide) stability.
Keywords
leaving, group, E1, reactivities, alkyl, halide
11-03
Title
Figure 11.3
Caption
Reaction coordinate diagram for the E2 reaction of 2-bromopentane with ethoxide ion.
Notes
The more stable E alkene has the more stable transition state, so it is formed more rapidly than the Z alkene.
Keywords
figure, 11.3, reaction coordinate, diagram, E2, 2-bromopentane
11-03-00UN
Title
(E)- and (Z)-2-pentene
Caption
Electrostatic potential maps and structures of (E)-2-pentene and (Z)-2-pentene.
Notes
(Z)-2-Pentene is less stable because of steric repulsions between hydrogens attached to the methyl and ethyl groups situated on the same side of the double bond, as can be seen from the potential maps.
Keywords
(E)-2-pentene, (Z)-2-pentene, electrostatic, potential, maps
11-03-30UN
Title
Deuterium Kinetic Isotope Effect
Caption
Definition of deuterium kinetic isotope effect.
Notes
Deuterium kinetic isotope effects greater than 1.0 indicate that the bond attaching H or D to the molecule under study is being broken in the rate-determining step.
Keywords
deuterium, kinetic, isotope, effect

Title
Table 11.3 Summary of the Reactivity of Alkyl Halides in Elimination Reactions
Caption
Notes
Keywords

Title
Table 11.4 Stereochemistry of Substitution and Elimination Reactions
Caption
Notes
Keywords

Title
Table 11.5 Relative Reactivities of Alkyl Halides
Caption
Notes
Keywords

Title
Table 11.6 Summary of the Products Expected in Substitution and Elimination Reactions
Caption
Notes
Keywords
11-01-07T01
Title
Table 11.1 Effect of steric properties on distribution of products in an E2 reaction
Caption
Notes
Keywords
11-01-09T02
Title
Table 11.2 More substituted product/ Less substituted product
Caption
Products obtained from the E2 reaction of methoxide and 2-halohexanes.
Notes
The reaction with fluoride leaving group yields the less stable terminal alkene product predominantly. With fluoride as the leaving group, the transition state resembles the carbanion obtained by removing hydrogen from a carbon adjacent to the carbon bearing the leaving group more than it (the transition state) resembles the product alkene. Since a primary (terminal) carbanion is more stable than a secondary (internal) carbanion, this reaction yields mostly terminal olefin. The hydrogen is abstracted from the terminal carbon in preference to the internal carbon.
Keywords
table, 11.2, E2, methoxide, 2-halohexanes

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