Conducted tour

This mechanism is exactly analogous to the allylic rearrangement mechanism for nucleophilic substitution (p. 421). The UV spectra of allylbenzene and 1-propenylbenzene in solutions containing NH2 are identical, which shows that the same carbanion is present in both cases, as required by this mechanism. The acid BH protonates the position that will give the more stable product, though the ratio of the two possible products can vary with the identity of BH". It has been shown that base-catalyzed double-bond shifts are partially intramolecular, at least in some cases. The intramolecularity has been ascribed to a conducted tour mechanism (p. 766) in which the base leads the proton from one carbanionic site to the other ... 

Kende, A. S., Riecke, E. E. Allylidenecyclopropane-methylenecyclopentene energy surface. Evidence for a conducted tour mechanism. J. Am. Chem. Soc. 1972, 94, 1397-1399. 

The phrase conducted tour mechanism was coined by Cram to describe the removal of a proton by a base and its subsequent return to a different face of the same molecule from which it was removed [Ij. Originally, the conducted tour mechanism was postulated to explain the observation that rates of racemization of deuterated carbon acids were faster than hydrogen-deuterium exchange in solutions of potassium r rr-butoxide/rerf-butyl alcohol. Thus, the basic catalyst takes hydrogen or deuterium on a conducted tour of the substrate from one face of the molecule to the [other] (ref. [1], p. 101). This process was envisioned as a rotation of the carbanion within the solvent cage. We now recognize that the secondary amine forms a mixed aggregate with the enolate, such that the reprotonation (and perhaps conformational motion) is intrasupramolecular. ... 

Table 10 indicates that under suitable conditions the proton is transmitted from one site to the other as the conjugate acid of the base without significant exchange with the solvent. The ion pair (Eqn. 63) has a significant lifetime compared with diffusion of BH" " into the solvent. Both of these phenomena are termed isoracemisa-tions - the base catalyst takes hydrogen or deuterium on a conducted tour of the substrate from one site to another. 

Colonel Lourie, a former columnist for the Palestine Posty was now area public-relations officer for the Haganah, and was in charge of the conducted tour, under the supervision of one of the Palmach officers who was responsible for our personal safety. 

Do you have a designated individual thoroughly trained in the use of the fire system to conduct tours with the fire inspector, loss control personnel, etc. ... 

I have observed many individuals give presentations or conduct tours of their facilities to describe and showcase their lean efforts and I am always amazed at the level of passion they demonstrate. Lean thinkers are... 

Cowie, J.M.G. 1988. An ion conducted tour through some polymer electrolytes. Polym Int 47 20. 

It should be noted that isoinversion can also occur without a conducted tour mechanism. This has been observed again with 9-methylfluorene and t rt-butanol solvent, but with n-propylamine replaced by the base penta-methylguanidine. That an alternative mechanism is operative is indicated by the fact that a substituent such as dimethylamide no longer needs to be present. The base can provide a charge delocalization pathway for travel of the deuteron from one side of the planar ring system to the other without solvent exchange. The deuteron can thus add to either side of the plane, as is illustrated below ... 

Another ideal use of this new nriedium is to facilitate transfer of responsibility from one team leader to another. All of the experimental data can be made available in an organized format. Conducted tours involving audio and video clips can make the technology transfer efficient and effective. 

Sharing via conducted tours, white boards , and e-mail deprives us of the important visual cues of facial expre.s-sion, eye contact, voice intonation, and psychophysiologi-cal responses such as body movement, breathing, yawning, and eye movement. Learning how to substitute written cues for the visual ones is as difficult as learning how to speak effectively. 

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