The Competition between Elimination Pathways in the Reactions of a Wide Variety of Bases with 2-Fluoro- and 2-Chlorobutane in the Gas Phase.
Ab initio methods are used to examine the regio- and stereoselectivities of the elimination reactions of 2-fluorobutane and 2-chlorobutane with a series of nucleophiles (F(-), HO(-), CH3O(-), (CH3)3CO(-), NH2(-), CH3(-), H(-), Cl(-), HS(-), and PH2(-)). The data suggest that regiochemistry is most closely related to the nature of the transition state on the E2 spectrum with E1cb-like reactions favoring the least-substituted alkene product and E1-like reactions favoring the most-substituted alkene product. There appears to be no correlation between the extent of π-bond formation (as measured by the Cα-Cβ distance) and the preference for forming the more highly substituted alkene. The stereochemistry (E vs Z) is less sensitive to the nucleophile and is relatively constant with the exception of a few systems that appear to have long-range interactions that reduce the bias against the Z product. Comparisons with experimental results in solution show, with a few exceptions, similar reactivity trends in solution and the gas phase.
Department of Chemistry, University of Rochester , Rochester, New York 14627, United States.
William H
WH
Saunders
Department of Chemistry, Virginia Commonwealth University , Richmond, Virginia 23284, United States.
Scott
S
Gronert