Michinori Ōki

Switching of two amine ligands via an SN2-type mechanism in a coordinated form of 2,6-bis(N,N-dimethylaminomethyl)phenylboronates

Facile exchange between the intramoleculariy coordinated and uncoordinated amine ligands in the title compounds is evidenced by NMR spectroscopy in solution, whereas the dynamic process is frozen in the solid phase as shown by X-ray crystallography.

Experimental and theoretical studies on the isomerization of allyl thiocyanate to allyl isothiocyanate

The mechanism of isomerization of allyl thiocyanate to allyl isothiocyanate has been investigated both experimentally and theoretically. The kinetic study indicates that the reaction is unimolecular and is not ionic. The entropy of activation suggests strongly that the mechanism involves a cyclic transition state. The rate of reaction was retarded to a small extent in polar solvents relative to that in nonpolar solvents. Ab initio MO calculations indicate, in agreement with the experimental results, that the reaction proceeds through a cyclic transition state, one in which the SCN moiety is almost linear. Thus, this is a [3,3] sigmatropic rearrangement. The charge separation in the transition state was substantial. The retardation of the reaction in polar solvents was attributed to the difference in solvation in the original state and in the transition state.

Preparation and separation of all possible rotamers of a stereochemical analog of meso-tartaric acid: optically inactive and optically active isomers of (R,S)-2,2′-bis(methoxycarbonyl)-6,6′-dimethyl-9,9′-bitriptycyl

All the three possible rotamers of the title compound were separated by chromatography, and unambiguously identified by NMR and X-ray analysis. One of the isomers was optically inactive C i conformation. The other optical active forms were resolved to give a pair of enantiomers, which were characterized by optical rotation and CD spectra. Thus the optical inactivity of a compound such as meso -tartaric acid that can take C i conformation in solution, is now ascribed to that the molecule has an optically inactive C i conformer and equal amounts of optically active conformers, that are enantiomers, in solution.

Syntheses of ap- and ±sc-2,2′,3,3′-tetramethoxy-9,9′-bitriptycyl rotamers and optical resolution of the ±sc-form☆

Abstract Rotational isomers of 2,2′,3,3′-tetramethoxy-9,9′-bitriptycyl, of which ap form is of C 2 h symmetry whereas the sc forms C 2 , have been isolated. The optically active forms exhibit the following specific rotations at Na D line for chloroform solutions (concentration ca. 1%) at 25 °C: Dextrorotatory form +7.8°, levorotatory form −7.6°.

Substantial differences in the product distributions between thermolyses and photolyses of 2-thiono-1-pyridyl 3-(1,4-dimethyl-9-triptycyl)-3-butanoate ester and the effects of rotational isomerism☆

Abstract The product distribution in the thermolysis of the title compound was found to be substantially different from that in the photolysis. The product distribution was also affected by the rotational isomerism of the compound.

2-Fluoro-4,4,5,5-tetramethyl-1,3-dioxolane: A compound carrying two independent probes for determining rates of formations of contact and solvent-separated ion pairs

Abstract 2-Fluoro-4,4,5,5-tetramethyl-1,3-dioxolane was shown to be a useful compound for independently determining the rate constants of contact ion pair and solvent-separated ion pair formations. The compound was used to determine rate constants for toluene-d 8 and chloroform-d solutions and they were found to be identical for each solution.

Barriers to Rotation

Barriers to rotation can in principle be determined by various methods. However, since we are interested in rather high barriers, the methods that can be used are limited. Those which are useful in this context are the dynamic NMR method and the classical method that uses the analysis of each rotational isomers by various methods. Since the classical method is considered to be measuring the reaction rates that are observed in the isomerization of rotational isomers, it is nothing but a kinetic measurement.

MANIFESTATION OF A (DISTORTED) TRIGONAL PYRAMIDAL STRUCTURE OF A QUADRIVALENT CARBON

Abstract Reactions of ap- and sp-rotamers of 1-(9-fluorenyl)-2-(1-methylethenyl)-naphthalene with m-chloroperoxybenzoic acid afforded the corresponding epoxides. Of these, the ap-epoxide was found to contain a carbon atom, the structure of which is a distorted trigonal pyramid, the carbon atom being located close to the center of the base triangle.

Synthesis and reactivity of 2-(ethylthio) phenylcopper: A stable organocopper compound carrying an intramolecular sulfane ligand

Abstract An unusually stable organocopper compound carrying an intramolecular sulfane ligand, 2-(ethylthio)phenylcopper, was synthesized via the reaction of the corresponding organolithium with a copper(I) halide (CuX). This compound was obtained in two forms: one is a salt-free compound which is insoluble in ordinary solvents, the other is a soluble complex of [2-(ethylthio)phenylcopper] 2 · CuX composition. These compounds were either hydrolyzed or underwent a coupling reaction to produce a biphenyl when heated. While these organocoppers are less reactive towards various electrophiles than other known arylcoppers, the soluble complex gives ketones with acyl halides in low yields. The properties as well as the reactivities of the stable organocopper compounds are reported.

Reactivity of Rotational Isomers

In this chapter, various findings on the reactivity of rotational isomers, including the rates of reactions, products, and reaction mechanisms, will be reviewed. The readers will find examples that convince them to think that the rotational isomers are really different compounds if they are diastereomers. The examples will further illustrate that a pair of rotational isomers are excellent for showing a detailed facet of reaction mechanisms and weak molecular interactions that affect the fate of unstable reaction intermediates.