Search results for "force"
showing 10 items of 3423 documents
4-Bromophenyl 2,4-dibromophenyl ether
2002
The title compound, C12H7Br3O, belongs to a group of flame retardants known as polybrominated diphenyl ethers (PBDE). Salient features of the packing of the title compound are infinite intermolecular Br⋯Br contact chains along the b direction.
A new type of pi-electron donors with one dithiole unit: Substituted 7-(1,3-dithiol-2-ylidene)-7-hydrobenz[d,e]anthracenes
1999
New electron donors 11a–c bearing only one 1,3-dithiole ring conjugated with an acene backbone have been synthesized by Wittig–Horner reactions from 7H-benz[d,e]anthracen-7-one (10) and differently substituted phosphonate esters 9a–c. The donor properties of 11 have been characterized by means of both experimental techniques and quantum chemical calculations. Cyclic voltammetry measurements on the novel compounds predict donor abilities comparable to those of TTF and BEDT-TTF. The voltammograms show a multi-stage redox behaviour with oxidation up to the trication, where the first two oxidation processes take place at very close potentials. These processes have been assigned to a simultaneou…
Red- and Blue-Shifts in Oligo(1,4-phenyleneethynylene)s Having Terminal Donor−Acceptor Substitutions
2004
Four series of oligo(1,4-phenyleneethynylene)s (OPEs), 1−4 (a−d), each having a terminal dialkylamino group as their electron donor, were prepared by applying Sonogashira−Hagihara reactions and a protecting group strategy. To study the influence that the push−pull effect has on the long-wavelength absorption, three of the four series of OPEs contain terminal acceptor groups (CN, CHO, NO2). Extending the conjugation (increasing the number of repeat units, n) lowers the energy E(n) of the electron transition in the purely donor-substituted series 1a−4a (bathochromic shift). This effect is superimposed in the push−pull series 1−4 (b−d) by the effect of the intramolecular charge transfer (ICT),…
A DFT study for the formation of imidazo[1,2-c]pyrimidines through an intramolecular Michael addition
2006
The formation of imidazo[1,2-c]pyrimidines through a ring closure of 2-(2-sulfonylimino-1,2-dihydro-1-pyrimidinyl) acetamides has been studied using DFT methods. Analysis of the energy results for the cyclization step shows the demand of almost an acid catalyst, which increases the electrophilicity of the dihydropyrimidine moiety, in order to make feasible the intramolecular Michael addition. The substitution on both dihydropyrimidine and amide moieties has also an influence on the cyclization step.
Enantioselective organocatalytic intramolecular aza-Michael reaction: a concise synthesis of (+)-sedamine., (+)-allosedamine, and (+)-coniine
2007
The intramolecular aza-Michael reaction of carbamates bearing remote alpha,beta-unsaturated aldehydes under organocatalytic conditions took place with good yields and excellent ee's when Jorgensen catalyst IV was used in the process, giving rise to the enantioselective formation of several five- and six-membered heterocycles. The developed methodology was applied to the synthesis of three piperidine alkaloids.
Self-assembly through non-coordinating intermolecular forces, part 2 [1]. Synthesis, crystal structure and packing of [Cu2(μ-phthalazine) 3(phthalazi…
2008
Abstract Treatment of the copper(I) trifluoromethanesulphonate toluene complex {[Cu(CF3SO3)]2 · C6H5Me} (1) with phthalazine (phtz, C8H6N2) in dichloromethane-acetonitrile solution yielded, via the bis(acetonitrile)tris(μ-phthalazine)dicopper(I) trifluoromethanesulphonate intermediate (2), the novel bis(phthalazine)tris(μ-phthalazine)dicopper(I) trifluoromethanesulphonate salt (3). Compound 3 was completely characterised and the molecular structure determined by single-crystal X-ray diffraction. Complex 3 crystallises in the monoclinic system, space group C2/c, with a = 26.9527(10), b = 10.9558(7), c = 19.2104(10) Å , β = 127.268(2)◦, V = 4514.3(4) Å3 and Z = 4. The copper(I) coordination g…
(1Z,3Z)-1,4-Di(pyridin-2-yl)buta-1,3-diene-2,3-diol: The Planar Highly Conjugated Symmetrical Enediol with Multiple Intramolecular Hydrogen Bonds
2002
1H, (13)C, and (15)N NMR spectral data show that in chloroform solution (1Z,3Z)-1,4-di(pyridin-2-yl)buta-1,3-diene-2,3-diol, OO, is in ca. 9:1 equilibrium with (3Z)-3-hydroxy-1,4-di(pyridin-2-yl)but-3-en-2-one, OK, while no 1,4-di(pyridin-2-yl)-2,3-butanedione, KK, was detected. The species present in the tautomeric mixture were identified by comparing their experimental chemical shifts with those known for similar compounds as well as with the theoretically calculated (GIAO-HF/DFT) values. Ab initio calculations show that OK and especially the highly conjugated OO forms are preferred in the tautomeric mixtures both in vacuo and in chloroform solution. Comparison of experimental (Arrhenius)…
Syntheses, crystal structures and magnetic properties of polynuclear 1,4,5,8,9,12-hexaazatriphenylene (hat)-bridged copper(II) complexes
2001
Three polynuclear compounds containing copper(II) and 1,4,5,8,9,12-hexaazatriphenylene (hat) as the basic building blocks have been prepared, [Cu4(hat)2Cl8]n·6nH2O 1, [Cu(hat)(H2O)2]n[NO3]2n2, and [Cu2(hat)(H2O)6]n[SO4]2n·2nH2O 3, their crystal structures determined and variable-temperature magnetic susceptibility data measured. The basic building block in 1 is the dinuclear [Cu2(hat)Cl4] entity, two such units being connected to tetranuclear units through relatively strong axial Cu–Cl bonds (out-of-plane di-μ-chloro bridges). Weaker axial Cu⋯Cl interactions link the units into a sheet structure. In 2 and 3 hat-bridged copper(II) chains extending along glide planes are present. hat serves a…
1-Chloro-1,1-difluoro-N-(4-methoxyphenyl)-3-(pyrrolidin-2-ylidene)propan-2-imine
2000
In the title compound, C(14)H(15)ClF(2)N(2)O, the Z configuration has been confirmed. The molecular structure shows an intramolecular N-H.N hydrogen bond [H.N 2.04 (6), N.N 2.709 (6) A and N-H.N 124 (5) degrees ]. This interaction could be responsible for the Z configuration.
Substituent and temperature controlled tautomerism of 2-phenacylpyridine: the hydrogen bond as a configurational lock of (Z )-2-(2-hydroxy-2-phenylvi…
2000
2-Phenacylpyridines substituted in the benzene ring are in equilibrium with (Z)-2-(2-hydroxy-2-phenylvinyl)pyridines when dissolved in chloroform. The substituent affects significantly the tautomeric equilibrium [the amount of the enolimine form stabilized by the intramolecular hydrogen bond is 1 and 92% for R = p-N(CH2)4 and p-NO2, respectively]. The negative logarithm of the tautomeric equilibrium constant, KT, is linearly dependent on the Hammett σ substituent constants. The dependence of KTvs. temperature is exponential in character: the more electron-withdrawing is the substituent, the more distinct is the influence of temperature. Unexpectedly, the tautomer present in the crystalline …