Substituents In Equatorial Positions Research Articles

Crystal structure of (-)-4R,5R-(2R,3R-butylenedioxy)-3,7-dimethyltetrahydropurine- 2,6,8-trione, C11H16N4O5

Article Crystal structure of (-)-4R,5R-(2R,3R-butylenedioxy)-3,7-dimethyltetrahydropurine- 2,6,8-trione, C11H16N4O5 was published on December 1, 1999 in the journal Zeitschrift für Kristallographie - New Crystal Structures (volume 214, issue 4).

Molecular and crystal structures of stereoisomeric2R,3R,6S-2-(1′S-hydroxy-1′-biphenylyl)- and2R,3R,6S-2-(1′R-hydroxy-1′-biphenylyl)methyl-3-methyl-6-isopropylcyclohexanones

It was established by X-ray diffraction analysis that 2-(1′-hydroxy-1′-biphenylyl)methyl-3-methyl-6-isopropylcyclohexanone, one of the minor products of the directed aldol reaction of (−)-menthone bromomagnesium enolate with 4-phenylbenzaldehyde, has the2R,3R,6S, 1′R configuration. The characteristic features of the spatial structure of this β-hydroxyketone were compared with those of the major stereoisomeric product of the above-mentioned reaction. The latter has the2R,3R,6S,1′S configuration. In the crystals, both stereoisomers have the cyclohexanone ring in a chair-like conformation with the three substituents in equatorial positions and are characterized by the presence of the annelated (cis-fused) pseudoring with an −OH…O=C< intramolecular hydrogen bond. The structures of the stereoisomers differ in the orientation of the aryl group and the hydrogen atom at the C(1′) chiral center with respect to the cyclohexanone ring. The results of X-ray diffraction analysis were compared with the data of molecular mechanics calculation for the energetically most favorable conformations of the isolated molecules of β-hydroxyketones under study.

2-Methylthio-5-nitroso-6-N-(2,3,4-tri-O-acetyl-β-D-xylopyranosyl)amino-4(3H)-pyrimidinone

The title compound, C16H20N4O9S, has a strong intramolecular N—H⋯O hydrogen bond between the nitrosyl O atom and an adjacent N—H moiety [N⋯O 2.516 (8)Å]. The β-d-xylopyranosyl ring has a 4C1 conformation, with all non-H substituents in equatorial positions. Molecules are linked about 21 axes via intermolecular N—H⋯O hydrogen bonds [N⋯O 2.892 (8) Å].

P-Chlorophenyl 3,4,6-Tri-O-benzyl-2-deoxy-2-methylene-β-D-glucopyranoside

The title compound, C 34 H 33 ClO 5 , has a β configuration at the anomeric centre C1. The pyranose ring adopts a chair conformation with all the substituents in equatorial positions. The molecular packing is achieved through van der Waals interactions

Anti,anti-N-(2,6-Dimethyl-1,3,5-trithian-1-ylidene)-4-methylbenzenesulfonamide

The major product of the dimethylation of the tosylimide of 1,3,5-trithiane is shown to be the title compound, C 12 H 17 NO 2 S 4 , which has all the substituents in equatorial positions with respect to the 1,3,5-trithiane ring

Structure of 3-(3,5-dimethylpiperidino)-N-(p-chlorophenyl)succinimide

In the title molecule, 3-(3,5-dimethylpiperidino)-1-(4-chlorophenyl)-2,5-pyrrolidinedione (1), the N-(p-chlorophenyl) substituent is rotated by 68.8 o relative to the succinimide plane. The piperidinyl ring has a chair conformation with all substituents in equatorial positions; the conformation around the piperidino-succinimide C-N bond is staggered. Crystallization in P2 1 /c with a=8.804, b=6.472, c=29.075A, β=94.75°, Z=4, T=153K, R=0.052

Circular dichroism studies of optically active 1,3-dioxolan-4-ones in the vacuum ultraviolet region

The circular dichroism spectra of substituted 1,3-dioxolan-4-ones in the gas phase from 230–160 nm are reported. The Cotton effect sign in the n-π* region is dependent of the conformational equilibrium of the five-membered ring. Molecular mechanics (MM2) calculations show that the envelope conformer with bulky substituents in equatorial positions is the most preferred conformation. The circular dichroism corresponding to the Rydberg transitions is less conformationally dependent. Comparison of the dioxolanone (1) and the analogous dioxolane (6) spectra shows that the Rydberg transitions are mainly due to the promotion of electrons from the diether moiety.

Conformation studies of isomeric 1-acyloxy-2-(4-methoxybenzyl)-cyclohexanes by 1H NMR spectroscopy

The conformation of the cyclohexane ring and the p-methoxybenzyl substituent in the series of isomeric 1-acyloxy-2-(4-methoxybenzyl)cyclohexanes was studied by means of 1H NMR spectroscopy. In all the substances investigated the cyclohexane ring assumes chair conformation. trans-Isomers have both substituents in equatorial positions, while in cis-isomers the p-methoxybenzyl group is always equatorial and the hydroxy or acetoxy group axial.

ChemInform Abstract: PIMARICIN. VIII. STRUCTURAL AND CONFIGURATIONAL STUDIES BY ELECTRON IMPACT AND FIELD DESORPTION MASS SPECTROMETRY, CARBON‐13 (25.2 MHZ) AND PROTON (270 MHZ)‐NMR SPECTROSCOPY

Attempts to obtain a molecular ion from the polyene macrolide antibiotic pimaricin by EI and FD mass spectrometry were unsuccessful The loss of carbon dioxide and a varying number of water molecules from the molecular ion made a molecular-weight determination impossible 13C NMR spectroscopy of N-acetylpimaricin, its dodecahydroderivative, and of HH-2, a hydrogenation-hydrogenolysis product of N-acetylpimaricin, confirmed that the antibiotic has structure 3 containing a hemi-ketalic ring and lacking an OH group at C-8. The value of the anomeric coupling constant, Jc-1-h-1, indicates that the mycosamine moiety is β-glycosidically bound to the aglycone. The structure and configuration of the antibiotic have been studied by analysis of the 270 MHz 1H-NMR spectra of N acetylpimaricin and HH-2. By comparison of the two spectra and by extensive decoupling experiments, all signals in the spectrum of N-acetylpimaricin have been assigned to the protons in structure 3. From chemical-shift, coupling constant, and integral values, it was deduced that the mycosamine ring is pyranoid with a chair conformation, the hemi-ketal is 6 membered and occupies a chair conformation with the substituents in equatorial positions, the epoxy protons as well as the olefinic protons are trans to each other, and the antibiotic is diastereomerically pure.

Studies on tellurium-carbon bonded compounds: V. The crystal structure of 1,3-dimethylacetylacetone tellurium(II)

The structure of the title compound has been determined by the heavy-atom method from 1349 reflections, measured with a diffractometer, and refined by full-matrix least-squares methods to R 0.044. Crystals are monoclinic, space group B 2 1/ c , a = 23.53(3), b = 4.85(1), c = 16.10(2) Å, β = 111.5(1)°, z = 8. In the molecules of the complex a tellurium(II) atom is bonded to one bivalent 1,3-dimethylacetylacetone ligand via the α-carbon atoms [Te-C 2.202(8), 2.157(8) Å; C-Te-C 88.4(3)°] forming a heterocyclic ring of chair conformation with both methyl substituents in equatorial positions. The molecules are arranged into one-dimensional zig-zag polymers, about the 2 1 axes at x = 1 4 or 3 4 and z = 0 or 1 2 , by associations between the tellurium atoms. These associations have been observed in other compounds studied in previous parts of this series and the implications of these associations with regard to the colour of this and related tellurium compounds are investigated in the light of current theories. All hydrogen atoms have been located.

Pimaricin—VIII : Structural and configurational studies by electron impact and field desorption mass spectrometry, 13C (25.2MHz) and 1H (270 MHz)-NMR spectroscopy

Attempts to obtain a molecular ion from the polyene macrolide antibiotic pimaricin by EI and FD mass spectrometry were unsuccessful The loss of carbon dioxide and a varying number of water molecules from the molecular ion made a molecular-weight determination impossible 13C NMR spectroscopy of N-acetylpimaricin, its dodecahydroderivative, and of HH-2, a hydrogenation-hydrogenolysis product of N-acetylpimaricin, confirmed that the antibiotic has structure 3 containing a hemi-ketalic ring and lacking an OH group at C-8. The value of the anomeric coupling constant, J c-1- h-1 , indicates that the mycosamine moiety is β-glycosidically bound to the aglycone. The structure and configuration of the antibiotic have been studied by analysis of the 270 MHz 1H-NMR spectra of N acetylpimaricin and HH-2. By comparison of the two spectra and by extensive decoupling experiments, all signals in the spectrum of N-acetylpimaricin have been assigned to the protons in structure 3. From chemical-shift, coupling constant, and integral values, it was deduced that the mycosamine ring is pyranoid with a chair conformation, the hemi-ketal is 6 membered and occupies a chair conformation with the substituents in equatorial positions, the epoxy protons as well as the olefinic protons are trans to each other, and the antibiotic is diastereomerically pure.