Search results for "Benzene"
showing 10 items of 1701 documents
Low-temperature methyl group dynamics of hexamethylbenzene in crystalline and glassy matrices as studied by 2H NMR
1991
Abstract 2 H NMR spectra of hexamethylbenzene (HMB) in protonated crystalline and amorphous matrices at low temperatures are presented. All spectra reveal lineshape changes which can be attributed to methyl group tunnelling. Compared to neat HMB, a drastic increase of the tunnelling frequency is found for all systems. This indicates that the hindering potential originates predominantly from intermolecular forces. We studied the temperature dependence of these spectra and the spin-lattice relaxation in order to exclude a distribution of motional correlation times describing a thermally activated process. In addition, we find a distortion of the methyl tetrahedron.
Relations between compression and thermal contraction in 1,2,4-trichlorobenzene and melting of trichlorobenzene isomers
2015
The compression and thermal expansion of crystalline 1,2,4-trichlorobenzene, C6H3Cl3, 124TCB, investigated under isobaric and isothermal conditions, are in reverse relation, as for most of crystals, however, the isochoric strain along direction c is clearly different from those along a and b. Single crystals of 124TCB have been in situ grown under isochoric and isobaric conditions, at 270 K/0.1 MPa and 295 K/0.16 GPa, and also at 100 K/0.1 MPa and 295 K/0.64 GPa, when the unit-cell volume is similar. All crystallizations yielded the same phase, of monoclinic space group P21/n, with two symmetry-independent molecules (Z′ = 2). The structure is governed by Cl⋯Cl and Cl⋯H interactions and the …
{[Hg(SCN)3]2(n-L)}2-: An Efficient Secondary Building Unit for the Synthesis of 2D Iron(II) Spin-Crossover Coordination Polymers
2018
[EN] We report an unprecedented series of two-dimensional (2D) spin-crossover (SCO) heterobimetallic coordination polymers generically formulated as {Fe-II[(He(SCN)(3))(2)](L)(x))}center dot Solv, where x = 2 for L = tvp (trans-(4,4'-vinylenedipyridine)) (1tvp), bpmh ((1E,2E)-1,2-bis(pyridin-4-ylmethylene)hydrazine) (1bpmh center dot nCH(3)OH; n = 0, 1), by eh ( (1E,2E)-1,2-bis (1-(pyridin-4-yl) ethyliden e) hydrazine) (Ibpeh center dot nH(2)O; n = 0, 1) and x = 2.33 for L = 0 0 bpbz (1,4-bis(pyridin-4-yl)benzene) (1bpbz center dot nH(2)O; n = 0, 2/ 3). The results confirm that self-assembly of Fell, [Hg-II(SCN)(4)](2-), and ditopic rodlike bridging ligands L containing 4-pyridyl moieties f…
Sodium-mediated manganation: direct mono- and dimanganation of benzene and synthesis of a transition-metal inverse-crown complex.
2007
Inside out approach: Twofold deprotonation of benzene by a sodium monoalkyl bisamido manganate(II) reagent derived from BuNa, 2,2,6,6-tetramethylpiperidine, and Mn(CH2SiMe3)2 has produced the first inverse-crown complex in which the transition-metal atoms are incorporated in the host (see X-ray structure, blue N, green Na, purple Mn). Variable-temperature magnetization measurements show that the complex is antiferromagnetic.
Conductance in isodielectric mixtures. I.n-butyronitrile with dioxane, benzene, and carbon tetrachloride
1974
The conductance of tetrabutylammonium tetraphenylboride, picrate, nitrate, and bromide has been measured at 25°C inn-butyronitrile and in mixtures of this solvent with dioxane, benzene, and carbon tetrachloride covering the range of dielectric constants from 10–24.26. For the picrate, nitrate, and bromide, the association constants at a given dielectric constant are independent of the chemical composition of the solvent. The changes of Walden products with solvent composition, however, are different, depending on which other solvent is mixed with the butyronitrile.
Conductance in isodielectric mixtures. III.i-butyronitrile with chlorobenzene,o-dichlorobenzene,p-dichlorobenzene, 1,2-dichloroethane, andn-pentanol
1975
The conductance of tetrabutylammonium tetraphenylboride, picrate, perchlorate, and nitrate has been measured at 25°C in mixtures ofi-butyronitrile with chlorobenzene,o-dichlorobenzene,p-dicholorobenzene, 1,2-dichloroethane, andn-pentanol covering the range of dielectric constants 10≤D≤20. In these mixtures of polar solvents, both association constants and ionic mobilities depend on ion-solvent interaction energies and on free volume in a manner that is specific for each system. This failure of the primitive model (rigid charged spheres in a continuum) is shown to be the consequence of short-range spatial and energetic interactions between ions and adjacent solvent molecules.
Isolation of Free Phenylide-like Carbanions with N-Heterocyclic Carbene Frameworks
2009
A series of 1,3-bis(2,6-diisopropylphenyl)-5-methyl-1,3-diaza-4,6-diborabenzenes with methyl, phenyl, and dimethylamino substituents on the ring boron atoms were prepared using the cyclocondensation reaction between N,N'-bis(2,6-diisopropylphenyl)trimethylsilylformamidine and the appropriately substituted 1,1-bis(organochloroboryl)ethane, followed by deprotonation of the cationic ring intermediate. The planar, heterocyclic benzene analogues could be further deprotonated at the other ring carbon using an additional equivalent of potassium hexamethyldisilazide to yield organometallic derivatives akin to the potassium phenylide. The potassium cations could be efficiently sequestered in both so…
Organotin(IV) complexes ofN-[(2Z)-3-hydroxy-1-methyl-2-butenylidene]glycine
2003
Organotin(IV) derivatives of N-[(2Z)-3-hydroxy-1-methyl-2-butenylidene]glycine have been synthesized and characterized by 1H, 13C, 119Sn NMR, 119Sn Mossbauer, and IR spectroscopy along with elemental analyses. The di- and triorganotin(IV) complexes were readily obtained from the reactions of organotin halides and sodium/potassium N-[(2Z)-3-hydroxy-1-methyl-2-butenylidene]glycinate. The diorganotin compound reacted with Ph3SnCl in refluxing benzene to give the mixed organotin dinuclear complex of composition Ph2Sn(2-OC(CH3)-C(H)C(CH3)NCH2COO)·Ph3SnCl, which was characterized by single crystal X-ray structure determination. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:149–154, 2003; Publ…
A statistical study of the additivities of substituent effects in the13C NMR chemical shifts of hydroxy- and chloro-substituted benzenes
1980
The 13C NMR spectra of six hydroxybenzenes, all chlorobenzenes, all chlorophenols and eight chlorocatechols are measured and assigned. The additivity of the substituent effects and the usefulness of some corrective parameters are studied with regression analysis. The order of the chemical shifts is most efficiently predicted by the simplest substituent effect model, containing only the direct effects of the substituents, although the 95% confidence limits of the calculated shifts are as high as 5.6 ppm. If the chemical shifts need to be predicted within the measuring errors (approximately 0.05–0.10 ppm, in the present data), the number of necessary corrections is very impractical. The corre…
Reaction of complex ligands: Part 95. Chromium tricarbonyl complexes of polysubstituted naphthohydroquinones: regioselective synthesis via [3+2+1]-be…
2003
Abstract A series of polysubstituted naphthohydroquinoid tricarbonyl chromium complexes were prepared by chromium mediated [3+2+1]-benzannulation of Fischer-type carbene complexes with alkynes. The kinetics and the thermodynamic data of the η6-η6-haptotropic rearrangements were investigated by in-situ NMR spectroscopy. The free activation energies ΔG# range from 23 to 26 kcal mol−1 and only slightly depend on the bulk and the donor/acceptor properties of the substituents. Equilibrium of metal migration was observed for naphthohydroquinone complexes bearing methoxy substituents at the non-hyroquinoid ring (ring A). In complexes bearing methyl groups or only hydrogen substituents at ring A th…