Search results for "Cyclohexane conformation"
showing 10 items of 52 documents
Über polygermane
1985
Abstract [(Cl 3 CCOO)Ph 2 Ge] 2 reacts with wet acetone to give Ph 8 Ge 4 O 2 , and with dry H 2 S to give Ph 8 Ge 4 S 2 . With Na 2 S or NaHSe, Ph 4 Ge 2 Cl 2 yields Ph 8 Ge 4 S 2 and Ph 8 Ge 4 Se 2 , respectively. Only Ph 6 Ge 3 S 2 or Ph 6 Ge 3 Se 2 , but no Ph 6 Ge 3 O 2 , can be obtained from a mixture of Ph 4 Ge 2 Cl 2 , Ph 2 GeCl 2 and Na 2 S or NaHSe. The mass spectra show a high stability of the cations Ph 6 Ge 3 S 2 + and Ph 6 Ge 3 Se 2 + . The 13 C NMR phenyl signals for C( ipso ) shift to high field in the series O, S, Se and 6-membered, 5-membered rings. The crystal structures of Ph 8 Ge 4 O 2 ( R = 0.031) and Ph 6 Ge 3 S 2 ( R = 0.036) have been determined. The 6-membered ring…
(E)-2-{[1-(3,11-Dimethyl-4-methylene-10-oxo-1-phenyl-4,5,10,11-tetrahydro-1H-benzo[b]pyrazolo[3,4-f][1,5]diazocin-5-yl)ethylidene]amino}-N-methyl-N-(…
2013
The central eight-membered ring of the title compound, C40H36N8O2, deviates from the ideal boat conformation because the bond between the exo-ethylene group and the adjacent N atom is twisted by 60.0 (4)° due to steric hindrance. Its adjacent benzene and pyrazole rings are oriented almost perpendicular to each other, making a dihedral angle of 85.8 (3)°. In the crystal, the molecules are linked by C(ar)—H...O hydrogen bonds, generating a three-dimensional network.
Modular P-Chirogenic Aminophosphane-Phosphinite Ligands for Rh-Catalyzed Asymmetric Hydrogenation: A New Model for Prediction of Enantioselectivity
2007
An original series of P-chirogenic aminophosphane-phosphinite (AMPP) ligands has been synthesized from (+)- or(–)-ephedrine in 23 to 61 % overall yields by a versatile three-step methodology. The AMPP ligands, bearing either one or two P-chirogenic centers, were used in the form of rhodium complexes for the catalyzed hydrogenation of α-acetamidocinnamate as a test reaction. Notably, even with AMPP ligands all derived from (+)-ephedrine, variation of the substituent on a P-center allowed the phenylalanine derivatives to be obtained in either (S) or (R) absolute configurations, with ee values ranging from 99 % (S) to 88 % (R). The asymmetric induction was analyzed with the aid of X-ray struct…
Benzoannulated quinone-type electron acceptors: evolution of the molecular and electronic structures upon reduction
1998
Abstract The molecular and electronic structures of DCNQI and its π-extended derivatives benzo-DCNQI and DCAQI have been investigated using ab initio 6-31G ∗ calculations. The steric hindrance introduced by lateral benzoannulation determines the loss of planarity of the DCNQI moiety for DCAQI. The most stable conformation of DCAQI corresponds to a butterfly-type structure, in which the DCNQI ring adopts a boat conformation and the lateral benzene rings remain planar. This structure lies 2.75 kcal mol −1 below the fully planar conformation. MP2/6-31G ∗ calculations including full geometry optimization confirm the greater stability of the butterfly structure. The geometries of the anions and …
Selective Derivatization of Resorcarenes. 3. C2-Symmetrical and Transcavity Bridged Bis-Benzoxazines Derived from C2v-Symmetrical Tetratosylates
1998
The regioselective condensation of resorcarene tetratosylates 3/4 with formaldehyde and various primary amines readily gives bis-benzoxazines 5/6 in 65−86% yield. The chiral, C2-symmetrical structure of these compounds has been proved by NMR-spectroscopy and single-crystal X-ray analysis. Bis-benzoxazines 5f and 5i assume in the crystalline state a boat conformation in which the two resorcinol rings bearing the oxazine fragments are nearly parallel. The tosylated resorcinol units are horizontally arranged in a propeller-like fashion, and two intramolecular hydrogen bonds are formed between the phenolic hydroxy groups and the oxygens of the neighboring sulfonyl fragments. Molecular mechanics…
Crystal structure and Hirshfeld surface analysis of 3-oxours-12-ene-27a,28-dioic acid (quafrinoic acid)
2017
The title compound, known as quafrinoic acid, is a pentacyclic triterpene isolated from Nauclea Pobeguinii. The compound is composed of five fused six-membered rings and the molecular conformation is stabilized by intramolecular C—H⋯O interaction, forming S6 and S8 rings.
ChemInform Abstract: Preparation and Structure of (EtO)2P(O)CH2Si(Me)2CH2SnMe2Cl. A Six- Membered Chelate Ring with Chair Conformation and a P=O××. t…
2010
A new series of π-extended tetrathiafulvalene derivatives incorporating fused furanodithiino and thienodithiino units: a joint experimental and theor…
2004
A new family of tetrathiafulvalenes has been prepared. The materials exhibit complex redox behaviour related to the electronic influence of the 1,4-dithiin moieties embedded within the framework of the molecules. The X-ray crystal structure of compound 4 reveals an unusual non-planar conformation of the heterocyclic compound, with the TTF fragment adopting a boat conformation. Theoretical calculations, performed at the DFT level (B3P86/6-31G*), confirm the boatlike structure (C2v symmetry) as the most stable conformation for this family of tetrathiafulvalenes. Upon oxidation, electrons are extracted from the whole molecule and the radical cations and dications remain highly distorted from p…
The Structural Diversity of Benzofuran Resorcinarene Leads to Enhanced Fluorescence
2014
An unexpected and previously unknown resorcinarene mono-crown with a fused benzofuran moiety in its macrocyclic core was obtained as a byproduct from a bridging reaction of tetramethoxy resorcinarene with tetraethylene glycol ditosylate. The formation of the fused benzofuran moiety in the resorcinarene macrocycle resulted in a unique rigid and puckered boat conformation, as shown by XRD studies in the solid state. Modification of the macrocycle was also observed to affect the photophysical properties in solution by enhancing the fluorescence brightness compared with a conventional resorcinarene macrocycle. The fluorescent properties enabled unique detection of structural features, that is, …
Twisting of the resorcinarene core due to solvent effects upon crystallization
2009
The effect of the crystallization conditions on the conformation of the tetramethoxy resorcinarene skeleton was investigated in acetone solutions, to which was added a second component (less favorable solvent or salt) to promote crystallization. The resorcinarene core was found to adopt three different conformations: crown (I), a pinched crown (II) and a twisted pinched crown (III). In addition, the flexibility of the resorcinarene core was compared with a tetramethoxy resorcinarene derivative, resorcinarene bis-crown, which is in a fixed boat conformation.