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Rotational Isomers (rotational + isomer)
Selected AbstractsBis(trifluoromethyl)phosphinous Acid (CF3)2P-O-H: An Example of a Thermally Stable Phosphinous Acid,Synthesis, Gas-Phase Structure, and Rotational IsomersCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2006Berthold Hoge Priv.-Doz. Abstract The bis(trifluoromethyl)phosphinous acid, (CF3)2POH, is the only known example of a thermally stable phosphinous acid. Although this compound has been known since 1960, little is known about the chemistry of this extraordinary compound; this might be due to the tedious, and in some part risky, synthesis that was originally published. An improved, simple, and safe synthesis that is based on the treatment of the easily accessible (CF3)2PNEt2, with at least three equivalents of p -toluene sulfonic acid, is presented. The reaction results in a complete conversion to the phosphinous acid, which is isolated in almost 90,% yield. The compound exists in an equilibrium of two POH rotational isomers, a fact which is supported by quantum chemical calculations. The relative enthalpy difference of 6.4 kJ,mol,1, calculated at the B3PW91/6-311G(3d,p) level, is in excellent agreement with the experimental value of 5.9 kJ,mol,1, which was determined from the temperature dependence of the (OH) bands of the two rotational isomers. The complete experimental vibrational spectra of both rotamers, their predicted vibrational spectra obtained by using quantum chemical calculations, and an attempt at photoinduced isomerization of matrix-isolated (CF3)2POH is presented. The experimental structure, obtained from an electron-diffraction study in the gas phase, is reproduced very well by ab initio and density functional theory (DFT) methods. [source] Structural and Electrochemical Studies of Dimerization and Rotational Isomerization in Multi-Iron SilicotungstatesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2005Travis M. Anderson Abstract A structural and electrochemical investigation of dimerization and Baker,Figgis (rotational) isomerization in the tri-ferric-substituted silicotungstates has been undertaken because these phenomena are important in a large number of polyoxometalates. A single-crystal X-ray diffraction analysis of K4Na7[(,-SiFe3W9(OH)3O34)2(OH)3] (,1) has been carried out [a = 12.9709(7) Å, b = 38.720(2) Å, c = 21.4221(12) Å, orthorhombic, Pbcm, R1 = 8.48,%, based on 13809 independent reflections]. The complex is isostructural with [(,-SiFe3W9(OH)3O34)2(OH)3]11, (,1) except that the edge-shared W3O13 caps in each [SiFe3W9(OH)3O34]4, unit are rotated by 60°. Electrochemical measurements, performed in a pH 5 acetate buffer, indicate a positive shift in the FeIII -based peak potential (and no change for the WVI -based potential) upon going from ,1 to its monomeric derivative [(,-Si(FeOH2)3W9(OH)3O34)]4, (,2) (,0.484,±,0.005 V and ,0.474,±,0.005 V, respectively). In contrast, the peak potentials of the FeIII - and WVI -based redox processes of ,1 are both found at more negative values than its rotational isomer ,1. The absolute values of the reduction peak potential differences are 0.022 V for FeIII and 0.162 V for WVI. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] 5-Chloro-3-methylthio-1,2,4-thiadiazol-2-ium chlorides as useful synthetic precursors to a variety of 6a,4 -thiapentalene systemsHETEROATOM CHEMISTRY, Issue 1 2003Georges Morel Title salts 3 were easily obtained by treatment of formimidoyl isothiocyanates 1 with a twofold excess of methanesulfenyl chloride. They showed interesting chemical behavior toward several nitrogen and carbon nucleophiles. Substitution reactions with isothioureas and acetamide in the presence of triethylamine gave the 1H, 6H -6a,4 -thia-1,3,4,6-tetraazapentalenes 7 and 6H -6a,4 -thia-1-oxa-3,4,6-triazapentalene 9, respectively. Addition of p -toluidine furnished the 5-imino-thiadiazole derivatives 10, which reacted further with diverse heterocumulenes to yield the corresponding thiatriaza- and tetraazapentalene species 11. The N,N,-bis(1,2,4-thiadiazol-5-ylidene)diaminobenzenes 13 were also prepared and reacted with phenyl isothiocyanate. Two stable rotational isomers were separated for the 1,2-phenylene product 14b. Other ,-hypervalent sulfur compounds 16 were synthesized under similar conditions from salts 3 and methyl cyanoacetate or dimethyl malonate. The structural assignments were discussed on the basis of IR and NMR spectroscopic data and received additional support from X-ray analysis of substrate 16a. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:95,105, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10106 [source] Mixed Isobutylphobane/N-Heterocyclic Carbene Ruthenium- Indenylidene Complexes: Synthesis and Catalytic Evaluation in Olefin Metathesis ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Xavier Sauvage Abstract Two new second generation ruthenium(II) dichloride-indenylidene complexes [RuCl2(9-isobutylphosphabicyclo[3.3.1]nonane)(NHC)(3-phenyl-1-indenylidene)], where NHC=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) or its unsaturated imidazol-2-ylidene analogue (IMes), were isolated in high yields upon heating a tetrahydrofuran (THF) solution of the diphosphane complex [RuCl2(isobutylphobane)2(3-phenyl-1-indenylidene)] with a two-fold excess of the corresponding imidazol(in)ium-2-carboxylate zwitterions. Both products were characterized by 1H, 13C, and 31P,NMR spectroscopy, and the molecular structure of [RuCl2(isobutylphobane)(SIMes)(3-phenyl-1-indenylidene)] was determined by X-ray diffraction analysis. A close inspection of the packing structure revealed the presence of different types of intra- and intermolecular interactions that enhanced the global stability of the crystals, while low temperature NMR experiments showed the existence of two distinct rotational isomers due to the unsymmetrical nature of the phobane ligand. The catalytic activity of both compounds was assessed in olefin metathesis using benchmark ring-opening metathesis polymerization, ring-closing metathesis (RCM), and cross-metathesis reactions, and compared with those of related first and second generation ruthenium-benzylidene and indenylidene catalyst precursors. Kinetic studies confirmed the high thermal stability of the mixed isobutylphobane/N-heterocyclic carbene complexes, which suffered from a slow initiation efficiency compared to other catalytic systems based on the tricyclohexylphosphane ligand. However, the remarkable robustness of [RuCl2(isobutylphobane)(SIMes)(3-phenyl-1-indenylidene)] was beneficial for performing the RCM of diethyl 2,2-bis(2-methylallyl)malonate. Monitoring the formation of the ruthenium-methylidene active species [RuCl2(isobutylphobane)(SIMes)(CH2)] derived from this precursor further demonstrated its ability to sustain long reaction times and high temperatures required to carry out the RCM of tetrasubstituted olefins. [source] Ab initio study on N,N,,N, -triaminoguanidineJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2007Pansy Iqbal Abstract Electronic structure calculations and second-order delocalizations in N,N,,N,,-triaminoguanidine (TAG) have been studied by employing ab initio MO and density functional methods. There are total 10 rotational isomers on the potential energy (PE) surface of TAG. The effect of three amino groups substitution on guanidine (Gu) has been studied in terms of the primary and the secondary electron delocalizations in TAG by employing Natural Population Analysis (NPA). An increased electron delocalization is observed in protonated triaminoguanidine (TAGP) due to the three strong intramolecular hydrogen bonds and hence accounts for its extra stability. The increase in the electron delocalization upon protonation in TAG can be compared to that in guanidine. The absolute proton affinity (APA) of TAG is less than that of Gu. HOMA and NICS studies have been carried out to understand electron delocalization in TAGP. Copyright © 2007 John Wiley & Sons, Ltd. [source] Bis(trifluoromethyl)phosphinous Acid (CF3)2P-O-H: An Example of a Thermally Stable Phosphinous Acid,Synthesis, Gas-Phase Structure, and Rotational IsomersCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2006Berthold Hoge Priv.-Doz. Abstract The bis(trifluoromethyl)phosphinous acid, (CF3)2POH, is the only known example of a thermally stable phosphinous acid. Although this compound has been known since 1960, little is known about the chemistry of this extraordinary compound; this might be due to the tedious, and in some part risky, synthesis that was originally published. An improved, simple, and safe synthesis that is based on the treatment of the easily accessible (CF3)2PNEt2, with at least three equivalents of p -toluene sulfonic acid, is presented. The reaction results in a complete conversion to the phosphinous acid, which is isolated in almost 90,% yield. The compound exists in an equilibrium of two POH rotational isomers, a fact which is supported by quantum chemical calculations. The relative enthalpy difference of 6.4 kJ,mol,1, calculated at the B3PW91/6-311G(3d,p) level, is in excellent agreement with the experimental value of 5.9 kJ,mol,1, which was determined from the temperature dependence of the (OH) bands of the two rotational isomers. The complete experimental vibrational spectra of both rotamers, their predicted vibrational spectra obtained by using quantum chemical calculations, and an attempt at photoinduced isomerization of matrix-isolated (CF3)2POH is presented. The experimental structure, obtained from an electron-diffraction study in the gas phase, is reproduced very well by ab initio and density functional theory (DFT) methods. [source] | ||||||||||