Gary G. Christoph

The Cation H13O6+: A Short, Symmetric Hydrogen Bond

The H_(13)O_6+ ion has been found to exist as a discrete entity, forming when the cage compound [(C_9H_(18)_3(NH)_2Cl]+Cl is crystallized from hydrochloric acid solution. The aquo-cation H_(13)O_6 has crystallographic symmetry 2/m (C_(2h)). The central bond O••H••O is symmetric, with a length of 2.39 ± 0.02 angstroms; the four outer hydrogen bonds are asymmetric, with a length of 2.52 ± 0.01 angstroms. The cage compound consists of a chloride ion encapsulated within a triply bridged diammonium species, with hydrogen bond distances N(H)••Cl of 3.10 ± 0.01 angstroms.

Silver(I) ion catalyzed rearrangements of strained .sigma. bonds. 33. Benzoannulation as a probe of structural dimension and .pi.-electron distribution in elassovalenes. A mathematical model for the assessment of homoaromaticity

6,7-Benzoelassovalene has been synthesized from benzocyclobutene and 1,4-cyclohexadiene-1,2-dicarboxylic anhydride. This crystalline white solid undergoes rapid decomposition when exposed to air, but can be handled under an argon atmosphere. An x-ray crystal structure analysis is reported and the magnitudes of the nonbonded distances separating C/sub 2/--C/sub 3/ and C/sub 4a/--C/sub 8a/ are revealed. These factors are considered in evaluating the possible neutral homoaromatic nature of the molecule. The preparation of 5,6-benzoelassovalene, which must maintain semibullvalene character to avoid disruption of benzenoid aromaticity, has also been completed. The lability of this compound of 6,7-benzoelassovalene by a significant margin, and it unfortunately proved possible to characterize this compound only by mass spectrometry. NMR spectral data for 6,7-benzoelassovalene are presented, correlated with earlier findings, and analyzed in terms of a possible diamagnetic ring current. Lastly, a mathematical model has been devised which enables the magnitude of bonding interaction between homoaromatic centers to be evaluated.

Phosphorus-31 NMR spectrum and molecular structure of a dirhodium complex that contains a rhodiumrhodium bond, bridging diphenylphosphido ligands, and a tetrahedral rhodium

Abstract The syntheses, 31 P{ 1 H} NMR spectra, and a structure of “mixed” 1,5-cyclo-octadienebis(tertiary phosphine)dirhodium complexes possess a rhodiumrhodium bond, briding diphenylphosphido and two different stereochemistries around the rhodium atoms. One rhodium is tetrahedral and surrounded by four phosphorus atoms and the other rhodium (bonded to COD) is nearly planar.

Synthesis and structure of [Rh4(CO)5(μ-PPh2)5]−, a completely phosphide bridged tetrarhodium cluster

Abstract The synthesis, pre31P {pre1H} NMR spectrum, and structure of the first completely phosphide bridged rhodium cluster is described. This novel complex has an arachno (or “butterfly”) structure, with a dihedral angle of 124°, and contains only PPh2− groups as bridging ligands.

X-Ray crystal and molecular structure of kodo-cytochalasin-1

Kodo-cytochalasin-1 and cytochalasin H have been shown to be identical in structure and stereochemistry by single-crystal X-ray diffraction analysis; an inadvertant error in the stereochemistry at C(18) reported previously for cytochalasin H is corrected.

X-Ray crystal structure of cytochalasin H, a potent new [11]cytochalasan toxin

A toxic fungal metabolite isolated from an unidentified species of Phomopsis has been unambiguously identified by X-ray crystallographic analysis as an [11]cytochalasan, which is very similar to cytochalasin D, differing from it only in the lack of the ketone group at C-17.

Crystal structure of the photoaddition product of iodoform and 3,4,5-trimethylphenol

A light yellow photoaddition compound is formed when dichloromethane solutions of iodoform and 3,4,5-trimethylphenol are irradiated with unfiltered light from a mercury vapour lamp. Three-dimensional X-ray diffraction analysis of crystals of this compound has shown them to be 4-di-iodomethyl-3,4,5-trimethylcyclohexa-2,5-dienone, indicating that the photoaddition has proceeded wholly by attack by photolytically generated ·CHl2 radicals.The structure was solved by direct methods and refined by full-matrix least-squares to R 0·047 for 1437 diffractometer measured intensities. Crystals are orthorhombic, space group Pbca, with Z= 8 in a cell of dimensions: a= 17·023 ± 0·009, b= 10·559 ± 0·004, and c= 12·889 ± 0·019 A. Bond distances and angles are all reasonable.