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951.
Elmar Kaufmann Bruce Tidor Paul Von Ragu Schleyer 《Journal of computational chemistry》1986,7(3):334-344
Solvation energies of lithium first-row compounds LiX (X ? H, Li, BeH, BH2, CH3, NH2, OH, F) and of the lithium cation with the model solvents, water and ammonia, have been calculated ab inito (MP2/6-31 + G*//6-31G* with zero-point vibrational energy corrections at 3-21G//3-21G). The solvation energies are found to be remarkably constant: ?18.0 ± 1.2 and ?21.5 ± 1.3 kcal/mol for the hydrates and ammonia solvates, respectively. This independence on the nature of X is due largely to the ionic character of the LiX compounds (dipole moments 4.7–6.6 debye). The unexpectedly high solvation energies of the lithium molecule (?14.3 and ?17.8 kcal/mol, respectively) are due to the polarizability of Li2. At the same level, the lithium cation has interaction energies with H2O and NH3 of ?34.1 and ?39.7 kcal/mol, respectively. For the hydrates of LiOH and LiF cyclic structures with hydrogen bonds and somewhat increased solvation energies also are described. 相似文献
952.
G. Von Poelhsitz B. L. Rodrigues A. A. Batista 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(9):m424-m427
The crystal structures of [1,3‐bis(diphenylphosphino)ethane‐κ2P,P′](pyridine‐2‐sulfinato‐κ2N,S)(pyridine‐2‐thiolato‐κ2N,S)ruthenium(II), [Ru(C5H4NO2S)0.33(C5H4NS)1.67(C26H24P2)] or [Ru(pySO2)1−x(pyS)1+x(dppe)] (x = 0.67), (I), and [1,3‐bis(diphenylphosphino)propane‐κ2P,P′](pyridine‐2‐sulfinato‐κ2N,S)(pyridine‐2‐thiolato‐κ2N,S)ruthenium(II), [Ru(C5H4NO2S)0.355(C5H4NS)1.645(C27H26P2)] or [Ru(pySO2)1−x(pyS)1+x(dppp)] (x = 0.645), (II), are composed of neutral distorted octahedral RuII complexes with chelating pyridine‐2‐thiolate, pyridine‐2‐sulfinate and biphosphine ligands. The S atoms are trans to each other, while pairs of P and N atoms are in cis positions. Partial double‐bond character is observed for C—S. The crystal packing consists of monolayers stabilized by C—H⋯O and C—H⋯S interactions, and is affected by the alkyl‐chain lengths. 相似文献
953.
Donald R. Schreiber De Von Andres James Huebner Seyed Rahmani 《Journal of solution chemistry》1993,22(5):457-467
The heat of dilution of aqueous solutions of ZnCl2 and the heats of mixing H
m
of aqueous solutions of CdCl2, NiCl2, and ZnCl2 with NaCl solutions were measured at 25°C. The heats of mixing were made at constant ionic strengths of 0.5, 1.0, and 3.0 molal. The excess enthalpy equations of Pitzer were then fitted to the resulting heats of dilution and heats of mixing data. The resulting parameters are the temperature derivatives of the activity coefficient mixing parameters in the Pitzer system. 相似文献
954.
955.
Werner Stdeli Wolfgang Von Philipsborn Alexander Wick Ivan Kompi 《Helvetica chimica acta》1980,63(2):504-522
15N-NMR. spectra of mono- and diaminopyridines, and mono-, di- and triaminopyrimidines including trimethoprim and other dihydrofolate reductase inhibitors have been studied in neutral and acidic media. Complete chemical shift assignments are given. Ring-nitrogen shifts are discussed in terms of β-, χ- and δ-substituent effects of amino and alkyl groups. Protonation states in TFA- and FSO3H-solution and protonation increments for the 15N-shifts of ring and amino N-atoms are determined. A linear correlation is observed between amino substituent effects (Δδ(15N)) on the ring N-atom in aminopyridines and corresponding Δδ (13C) values in aminobenzenes and, similarly, between Δδ(15N) values in aminopyrimidines and Δδ(13C) values in aminopyridines. Assignment of the 15N-NMR. spectra of pyrimidine N-oxides, pyrazine N-oxides and pyridazine N-oxides is achieved by comparison with 14N-NMR. data and with the aid of Yb(fod)3-induced shifts. One-bond 15N, 1H-coupling constants are reported for aminopyridines and aminopyrimidines and discussed in terms of conjugative interaction between NH2-group and ring system. 相似文献
956.
Threshold energies (6.1 <Et ? 8.6 eV) are determined for photoelectron emission by 16 inorganic cations in aqueous solution Et values are correlated with gas-phase ionization potentials, solvation and reorganization free energies, standard reduction potentials and ligand field stabilization energies (five transition metals). Dielectric saturation is shown to drastically lower threshold energies. 相似文献
957.
Lech Kozerski Krystyna Kamienska-Trela Lidia Kania Wolfgang Von Philipsborn 《Helvetica chimica acta》1983,66(7):2113-2128
The pulse sequence INEPT was used to obtain proton-coupled 15N-NMR spectra in natural isotope abundance for enamines substituted in 2-position with electron-with-drawing groups. The chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as multiple N-alkyl substitution, double-bond configuration, H-bonding, N-lone-pair delocalization within the conjugated system, and steric effects. It is concluded that 15N chemical shifts are a sensitive probe for local structural modifications at the N-atom and conformational changes in a remote part of a conjugated molecule, while one-bond N,H-coupling essentially reflects N-hybridization and subtle local geometric distortions. Stereospecific three-bond N,H spin coupling to olefinic protons (4.0 ± 0.2 Hz) has been found a characteristic feature of (Z)-isomers in all investigated compounds, whereas two-bond coupling to olefinic protons (2J(N,H) = 0.5 to 5 Hz) is observed in (E)-isomers. The sensitivity to solvents and steric properties of remote substituents renders geminal coupling a useful probe for studying electronic effects in the C? N bond. 相似文献
958.
Jürgen Nuss Raúl Hector Cardoso Gil Wolfgang Hnle Karl Peters Hans Von Georg Schnering 《无机化学与普通化学杂志》1996,622(11):1854-1864
Synthesis, Structure, and Properties of the Tetraarsenidometallates(V) M7[TAs4] (M = K, Rb; T = Nb, Ta) The tetraarsenidometallates(V) M7[TAs4] (M = K, Rb; T = Nb, Ta) have been prepared from RbAs, KAs, Rb3As, K3As, and Nb or Ta in sealed Nb(Ta) ampoules at T = 1100 K. They crystallize in a new structure type oP24 (Pmn21, no. 31); K7[NbAs4]: a = 1019.2(2) pm, b = 916.2(2) pm, c = 830.6(1) pm; K7[TaAs4]: a = 1017.3(2) pm, b = 915.5(2) pm, c = 830.5(2) pm; Rb7[NbAs4]: a = 1059.2(4) pm, b = 952.8(4) pm, c = 860.4(4) pm; Z = 2 formula units per unit cell). The compounds form dark red crystals and they are sensitive against air and moisture. They are semiconductors with Eg = 1.80 eV. The thermal decomposition in dynamical vacuum gives evidence for the existance of K4TAs3 and K2TAs2 (T = Nb, Ta). Main structural units are polar oriented tetrahedra [TAs4] with d (T – As) = 252.2(1) pm; 251.3(1) pm; 253.0(4) pm, respectively. The As atoms are trigonal prismatically coordinated by M and T atoms. These trigonal prisms form anionic and cationic layers [M4As2]2? and ∞2[M3TAs2]2+ alternating along the b axis. The structure is comparable with that of Co2P and can be described as a stuffed shear variant of the Na6□ZnO4 type of structure. 相似文献
959.
Von Sonntag J Knolle W Naumov S Mehnert R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(18):4199-4209
The photochemistry of maleimide in aqueous solution is governed by the coexistence of up to three different triplet states, the keto triplet (lambda(max)=250, 330 nm, lambda(min)=290 nm, pK(a)=4.4+/-0.1, tau=5 micros), the deprotonated or enolate triplet (lambda(max)=360, 260 nm, lambda(min)=320 nm, shoulder at 370-380 nm) and a dimer triplet. This biradical is formed by the addition of the keto triplet to the double bond of a ground state maleimide in competition with electron transfer, (k( (3)MI+MI)=2.6 x 10(9) dm(3) mol(-1) s(-1)). Its spectrum is identical to that of the maleimide H-adduct radical (lambda(max)=370-380 (broad), 255 nm (narrow), lambda(min)=290 nm) and its lifetime is 110 ns. While protolysis is confined to maleimide and aqueous solutions, the dimer triplet is also found in acetonitrile. Dimer triplet formation is also observed with N-ethylmaleimide. Time-resolved conductometry and buffer experiments were used to characterise excited state protolysis. Multi-wavelength "global analysis" of the time profiles allowed the separation of the transient spectra and study of the kinetics of the monomer and dimer triplets. The cyclobutane dimer yield (determined by GC) is independent of maleimide concentration. This indicates that the dimer triplet does not contribute significantly to the initiation of free-radical polymerisation. Time-dependent Hartree-Fock calculations agree with the experimental data and further confirm the proposed mechanisms. 相似文献
960.
C. Von Sonntag 《Tetrahedron》1969,25(24):5853-5861
The UV photolysis (λ = 185 nm) of liquid methanol yields hydrogen, glycol, formaldehyde, methane and traces of ethane in quantum yields of 0·83, 0·78, 0·058, 0·05 and 0·002 resp. (related to φ(H2) = 0·4 of the ethanol-actinometer (5 mole/1 in water)). The isotopic distribution of the hydrogen (85% HD) formed in the photolysis of CH3OD shows, that as in the gasphase2 the scission of the O---H-bond (1) is the major process. CH3OH + hv (λ = 185 nm) → CH3O• + H• (1)
In methanoi-water mixtures (nearly all the light of the wavelength λ = 185 nm is absorbed by methanol) the quantum yields of hydrogen, glycol, methane and ethane are greatly reduced, while the formaldehyde yield remains unaffected. In 1 molar solution φ(H2) = 0·42, φ(glycol) = 0·32 and φ(CH4) = 6 x 10−4 is obtained. Ethane cannot be detected. 相似文献