[en] Deuteroxide/hydroxide kinetic isotope effects for the compounds p-(CH₃)₃N⁺C₆H₄CH₂CH₂X with various leaving groups X, whose syntheses are described herein, were determined at 60⁰ as follows (X, k/sub DO^-/k/sub HO^-): N⁺(CH₃)₃, 1.62 +- 0.12/ N⁺(CH₃)₂C₆H₅, 1.68 +- 0.02/ S⁺(CH₃)₂, 1.54 +- 0.02/ F, 1.66 +- 0.03/ Cl 1.40 +- 0.03/ Br, 1.30 +- 0.02+ These isotope effects are best interpreted as measuring different extents of proton transfer from C/sub beta to the attacking lyoxide ion in the concerted E2 transition state, and thus provide a series ranging from more-than-half transfer (isotope effects greater than ca. 1.41, the square root of the maximal isotope effect, ca. 2.0, for complete transfer) to less-than-half transfer. It is also suggested that the data available for E2 reactions best fit transition states which are ElcB-like for poor leaving groups and nearly central for good leaving groups. Significant perpendicular as well as parallel effects in the transition state geometry changes associated with structural changes in reactants explain the data, including the shift to ElcB-like transition states with poor leaving groups, which is considered to be the origin of the Hofmann and Saytzev orientation rules. A ''force formulation'' of a previously proposed theory of structural effects upon transition-state geometries is also outlined, as a clarification and aid to application of the theory. (U.S.)