A comment on the mechanism of enantiotopomerization of tetrahedral boron chelates; model MNDO calculations

1982 ◽  
Vol 0 (10) ◽  
pp. 542-543 ◽  
Author(s):  
Paul von Ragué Schleyer ◽  
Ernst-Ulrich Würthwein
Keyword(s):  
Boron Chelates ◽  
Mndo Calculations ◽  
Tetrahedral Boron

Energy barriers for the enantiotopomerization of tetrahedral boron chelates

1982 ◽  
pp. 169 ◽  
Author(s):  
Michail S. Korobov ◽  
Leonid E. Nivorozhkin ◽  
Leonid E. Konstantinovsky ◽  
Vladimir I. Minkin
Keyword(s):  
Energy Barriers ◽  
Boron Chelates ◽  
Tetrahedral Boron

Tautomerism of pyrazoline-5-thione and triazoline-5-thione studied by variable temperature photoelectron spectroscopy

1983 ◽  
Vol 61 (6) ◽  
pp. 1197-1203 ◽  
Author(s):  
Claude Guimon ◽  
Geneviève Pfister-Guillouzo ◽  
Mlkael Begtrup
Keyword(s):  
Gaseous Phase ◽  
Photoelectron Spectroscopy ◽  
Variable Temperature ◽  
Thermal Isomerization ◽  
Photoelectron Spectra ◽  
Planar Form ◽  
Mndo Calculations

Photoelectron spectra at variable temperatures demonstrate that the rate of thermal isomerization of pyrazoline-5-thione (1a) into methylthiopyrazole(s) in the gaseous phase is metal catalysed. Similar isomerizations of triazolethione (2a and 3a) are at best only slightly so.Furthermore, photoelectron spectra and MNDO calculations show that gaseous methylthiopyrazoles (1b and 1c) and methylthiotriazoles (2b and 2c) exist predominantly in planar form for the b isomer and in nonplanar form for the c isomer. The ΔH0 for the rotameric equilibria is 2.7–4.2 kJ•mol−1.

Structures of boron chelates of mono- and diacylketene aminals

1996 ◽  
Vol 45 (10) ◽  
pp. 2411-2416
Author(s):  
V. A. Dorokhov ◽  
L. G. Vorontsova ◽  
M. G. Kurella
Keyword(s):  
Boron Chelates

Chemistry of Fenchonesulfonic Acid Derivatives

1995 ◽  
Vol 50 (2) ◽  
pp. 283-288 ◽  
Author(s):  
Gabriele Wagner ◽  
Uwe Verfürth ◽  
Rudolf Herrmann
Keyword(s):  
Acetic Anhydride ◽  
Thionyl Chloride ◽  
Sulfonic Acid ◽  
Reaction Rate ◽  
Enantiomeric Excess ◽  
Methyl Group ◽  
Close Analogy ◽  
Chiral Sulfoxides ◽  
Mndo Calculations ◽  
Nmr Techniques

(1 S) - (+)-Fenchone is sulfonated by SO3 or H2SO4/acetic anhydride in the bridgehead methyl group. This could be confirmed by NMR techniques (INADEQUATE). The fenchonesulfonic acid obtained is converted (SOCl2/NH3) to the cyclic fenchonesulfonimide, which can be oxidized to the corresponding oxaziridine, in close analogy to 10-camphorsulfonimide. Improved procedures for this reaction sequences are given. During the treatment of the sulfonic acid with thionyl chloride, a byproduct with a rearranged bicyclic skeleton is observed whose structure has been determined by ozonolytic degradation and NMR techniques. A possible mechanism for this rearrangement is suggested, based on MNDO calculations of the intermediate carbocations. The fenchonesulfonyloxaziridine oxidizes sulfides to chiral sulfoxides with appreciable enantiomeric excess, but very low reaction rate. A comparison with camphor-derived oxaziridines having similar steric requirements is made.

Boron Chelates and Boron-Metal Chelates, X [1]. 3-(2-Hydroxyphenyl)-2,2-diphenyl-1-oxa-3-azonia-2-borata-naphthalene-methanol (1/1): Synthesis, Spectroscopic Investigations and Crystal Structure

1982 ◽  
Vol 37 (11) ◽  
pp. 1450-1455 ◽  
Author(s):  
Rudolf Allmann ◽  
Eberhard Hohaus ◽  
Stanislaw Olejnik
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonds ◽  
Structure Analysis ◽  
Title Compound ◽  
Chelate Ring ◽  
Boron Chelates ◽  
X Ray ◽  
Membered Chelate Ring ◽  
Compound C ◽  
Overall Ratio

The title compound, C25H20BNO2 · CH3OH, was examined by UV, IR, 1H, and 13C NMK spectroscopy as well as by thermogravimetry and X-ray structure analysis (Pbnb, a = 8.815, b = 17.309, c=28.992 Å, R= 5.5%). These investigations show the six-membered chelate ring (chelate A) to exist as formulated in [2] and not as a five-membered chelate ring B. One methanol molecule connects two chelate molecules by hydrogen bonds, resulting in an overall ratio of chelate to methanol of 1 : 1.

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