Hydrogen-deuterium isotope effects for the base promoted E2 reaction of quaternary ammonium ions. The effect of base, solvent, and structure on the nature of the transition state.

✍ Scribed by P.J. Smith; S.K. Tsui

• Publisher: Elsevier Science
• Year: 1973
• Tongue: French
• Weight: 204 KB
• Volume: 14
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)95577-7

✦ Synopsis

In a recent publication2 the mechanism of the reaction of i-arylethyltrimethylammonium ions with ethoxide ion in ethanol at 70° was shown to be E2. The transition state for this process involved extensive proton transfer to base as exhibited by the observed trend in hydrogendeuterium isotope effects 394,s with variation in para-substituent as well as the observation of a positive Hamrnett e value of iC.95.

In order to gain an insight into the effect of base and solvent on the nature of the transition state for an E2 process, we have determined the hydrogen-deuterium isotope effects as well as the Hammett rho for reaction of the l-arylethyl salts with t-butoxide in t-butanol at 30" and ethoxide ion in EtOH-DMSO mixtures at 70°. These results are shown in the Table along with the results obtained previously2 for reaction with ethoxide ion. The effect of a structural change on the nature of the transition state was investigated by studying the reaction of 2_substituted 9-methylfluorene-9-trimethylammonium ions with ethoxide6 at &Co and the results are shown in the Table.

The effect of solvent in determining the nature of the transition state for the reaction of the charged substrate with ethoxide was determined by varying the solvent composition from 100