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1.
McDowell SA Buckingham AD 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(7):1603-1609
The shift in the harmonic vibrational frequency of the ArH stretch of FArH on formation of the linear FArH...Rg complexes (Rg=He, Ne, Ar, Kr), and of the FH stretch on formation of the linear FH...Rg complexes, has been determined by ab initio computations. These shifts are in agreement with predictions from a model based on perturbation theory and involving the first and second derivatives of the interaction energy with respect to displacement of the ArH (FH) bond length from its equilibrium value in the monomer. In the FH...Rg dimers, small blue shifts were obtained for the He and Ne complexes and red shifts for those with Ar and Kr. In the FArH...Rg dimers, blue shifts were obtained for all four complexes. These vibrational characteristics are rationalized by considering the balance between the interaction energy derivatives obtained from the perturbative model. The bond length changes on complexation are also well predicted by the model. Our computations were restricted to the linear geometry since the objective was to investigate the validity of the perturbation model and to illuminate the causes of the red and blue shifts. 相似文献
2.
The change in the vibrational anharmonic constant for the linear hydrogen-bonded complexes FHRg, FArHRg, FArHN2, FArHP2 (Rg=Ne, Ar, Kr) was determined at the MP2/6-311++G(3df,3pd) level of theory. It was found that in the vibrationally red-shifted complexes, hydrogen bond formation increases the anharmonic constant while in the vibrationally blue-shifted species (except FArHNe) the anharmonic constant decreases on complexation. 相似文献
3.
Sean A. C. McDowell Ajit J. Thakkar 《International journal of quantum chemistry》2010,110(8):1506-1513
A simple model has been proposed to explain trends in the computed interaction energy, bond length changes, frequency shifts and infrared intensities for the chlorofluoromethanes CFnClmH, FH and FArH on complexation with the isoelectronic diatomics BF, CO, N2 and the rare gas atoms Kr, Ar, Ne to form a series of linear or nearly linear hydrogen‐bonded complexes. The dipole moment derivative of the proton donor (with respect to the stretching coordinate) and the chemical hardness of the hydrogen‐bonded atom of the proton acceptor are identified as two useful parameters for rationalizing the changes in some of the molecular properties of the proton donor when the hydrogen bond is formed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
4.
McDowell SA 《Journal of computational chemistry》2008,29(2):298-305
Bond length changes, harmonic vibrational frequency shifts, and changes in the proton magnetic shielding of HX and HKrX (X = F, Cl) on complexation with N2 to form the linear red-shifted N2 ... HX and linear blue-shifted N2 ... HKrX complexes were determined by ab initio computations, with and without counterpoise correction, at the SCF and MP2(full) levels of theory using a 6-311++G(2d,2p) basis set. The MP2 computations agree with predictions from a perturbation theory model involving the first and second derivatives of the interaction energy with respect to displacement of the H--X and H--Kr bond lengths from their equilibrium values in the isolated monomers. The theoretical results agree qualitatively with the experimentally observed frequency shifts, with near quantitative agreement for N2 ... HKrCl. The characteristic downfield shift of the isotropic proton magnetic resonance in the red-shifted complexes was obtained, but for the blue-shifted complexes, the proton NMR shifts to higher fields. 相似文献
5.
The nature of the intermolecular hydrogen bond for the furan-HCl and furan-CHCI3 complexes has been studied using ab initio calculations with MP2 level of theory. The new hydrogen bond type of C(CI)-H...O and π interactions are studied also. It
is shown that, for the optimized geometries of furan-CHCI3, C-H bond lengths contract and vibrational frequencies are blue-shifted, while for the furan-HCl complex, H-CI bond lengths
elongate and vibrational frequencies are red-shifted. In addition, the NBO analysis indicates that, for the furan-CHCI3 complex, the charge transfers from the lone pair of the proton acceptor to both σ *(CH) antibonding MO and lone pairs of
CI atom. 相似文献
6.
Proton magnetic resonance spectra of trans and cis-2,3-diphenylaziridine (1 and 2) and their N-ethyl derivatives 3 and 4 were measured in carbon tetrachloride, chloroform, and benzene-d6 at low temperatures (1 and 3) and in dry conditions (1 and 2). On the basis of these results it was concluded that an N-ethyl group exerts a shielding influence on a cis ring proton and a deshielding influence on a trans ring proton. From results obtained by measuring the 1H n.m.r. spectra of 1–4 in deuterochlorofom-trifluoroacetic acid it was derived that the lone pair of the aziridine nitrogen exerts a shielding influence on cis related ring hydrogens. In most N-alkylaziridines the effect of the N-alkyl group predominates. 相似文献
7.
Magnetic shielding constants are calculated for the protons in XOH and XOH…OH2 (XH, CH3, NH2, OH and F) molecules using a slightly extended set of atomic functions modified by gauge factors. These results are used to determine theoretical values for the NMR hydrogen bond shifts in the XOH…OH2 systems. Such theoretical data are consistent with the few available experimental data. An analysis of the theoretical results reveals that there are three major types of shielding contribution to the NMR hydrogen bond shift; (a) a deshielding change due to the variation of the local currents on the hydrogen bonded proton; (b) a reduction in shielding from currents localized on the oxygen atom of the proton donor; (c) a deshielding contribution from currents induced on the oxygen atom of the proton acceptor. Except for the water dimer, contributions (a), (b) and (c) are of comparable importance for changes in isotropic shielding. For (H2O)2 contributions (a) and (c) are somewhat more important than contribution (b). Contribution (c) is almost totally responsible for the changes in the anistropies of the shielding tensors associated with the hydrogen bonded protons. The proton shielding anisotropy changes which occur on hydrogen bond formation are generally much larger than the corresponding variations in the isotropic values of the shielding tensors. This suggests that proton magnetic shielding anisotropies may be more sensitive measures of features of hydrogen bonding than are isotropic proton shielding constants. 相似文献
8.
The hydrogen-bonded structures of the CH3OH complexes with CF4, C2F2, OC, Ne, and He are designated as the starting points for geometry optimizations without and with counterpoise (CP) correction
at MP2 level of theory with the basis sets 6-31+G*, 6-31++G**, and 6-311++G**, respectively. Tight convergence criteria are
applied throughout all geometry optimizations in order to reduce the computational errors. According to the optimizations
without CP correction, a blue-shifted O–H···Y (where Y = F, O, Ne, or He) hydrogen bond exists in all these five complexes.
The magnitudes of blue shifts of ν(O–H) of the former four complexes with respect to that of CH3OH are reduced greatly when the polarization and diffuse functions of the hydrogen atoms are added (results from 6-31+G* versus
those from 6-31++G**). However, for the complexes CH3OH–CF4 and CH3OH–C2F2, our optimizations using the CP corrections did not find the hydrogen-bonded structure to be a stationary point. The energy
minimum of both the complexes corresponds to a non-hydrogen-bonded structure. 相似文献
9.
Ab initio calculations are applied to examine the influence of the intermolecular interactions on the shielding constant in gaseous nitrogen. An accurate literature potential energy surface and the nuclear magnetic resonance shielding surface of the N2–N2 complex calculated in this work provide results in satisfactory agreement with the available experimental estimates of the effect. 相似文献
10.
Tao Liu Bao-Hui Xia Xin Zhou Qing-Chuan Zheng Qing-Jiang Pan Hong-Xing Zhang 《Theoretical chemistry accounts》2008,121(3-4):155-164
Electronic structures, absorptions and emissions of a series of (ppy)2Ir(acac) derivatives (ppy = 2- phenylpyridine; acac = acetoylacetonate) with fluoro substituent on ppy ligands were investigated theoretically. The ground and excited states geometries were fully optimized at B3LYP/LANL2DZ and CIS/LANL2DZ level, respectively. The HOMO is composed of d(Ir) and π(C∧N), while the LUMO is localized on C∧N ligand. The absorptions and emissions in CH2Cl2 media were calculated under the TD–DFT level with PCM model. The lowest-lying absorption of these complexes is dominantly attributed to metal-to-ligand and intraligand charge transfer (MLCT/ILCT) transitions and the emission of them originates from 3MLCT/3ILCT excited states. The absorption and emission of these complexes are blue-shifted by increasing the number of fluoro on phenyl, but the spectra are red-shifted by adding fluoro on pyridyl. While a single fluoro of different substituted site on phenyl results in different extent blue-shift to the spectra. 相似文献
11.
S. Schohl M. W. Müller H. A. J. Meijer M-W Ruf H. Hotop H. Morgner 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,16(4):237-249
Using crossed beams of metastable rare gas atoms Rg*(ms3 P 2,3 P 0) (Rg=Ne, Ar, Kr, Xe) and ground state sodium atoms Na(3s 2 S 1/2), we have measured the energy spectra of electrons released in the respective Penning ionization processes at thermal collision energies. For Rg*(3 P 2)+Na(3s), the spectra are quite similar for the different rare gases, both in width and shape; they reflect attractive interactions in the entrance channel with well depthsD* e [meV] decreasing slowly from Rg=Ne to Xe as follows: 676(18); 602(23); 565(26); 555(30). For Rg*(3 P 0)+Na(3s), the spectra vary strongly with the rare gas, indicating a change in the character of the interaction from van der Waals type attraction (Ne) to chemical binding for Kr and Xe with well depthsD* e [meV] of: 51(19); 107(25); 432(30); 530(50). These findings are explained through model calculations of the respective potential curves, in which the exchange and the spin orbit interaction in the excited rare gas and the molecular interaction between the two valences-electrons in terms of suitably chosen singlet and triplet potentials are taken into account. These calculations also explain qualitatively the experimental finding that the ratiosq 2/q 0 of the ionization cross sections for Rg*(3 P 2)+Na and Rg*(3 P 0)+Na vary strongly with the rare gas from Ne to Xe as follows: 15.8(3.2); 2.6(4); 1.4(2); 1.6(4). 相似文献
12.
《Journal of Coordination Chemistry》2012,65(12):2160-2170
Two pentagonal bipyramidal complexes, ethanol-(S-ethyl-N1,N4-bis(3-methoxy-2-hydroxybenzaldehyde)-isothiosemicarbazide-N,N′,O,O′)-dioxidouranium(VI) (1) and ethanol-(S-ethyl-N1-(2-hydroxyacetophenone)-N4-(5-bromo-2-hydroxybenzaldehyde)-isothiosemicarbazide-N,N′,O,O′)-dioxidouranium(VI) (2), have been prepared and characterized. Their structures have been determined by X-ray crystallography, and the structural parameters are discussed with those observed in related complexes. Electronic absorption, proton magnetic resonance, and FT-IR spectra have been recorded and analyzed. In both complexes, the U(VI) centers are surrounded by N2O2 donor ligands, two oxido groups, and one ethanol in a distorted pentagonal bipyramid. The thermal stability of the new complexes has also been determined. 相似文献
13.
Theoretical study of the intermolecular hydrogen bond interaction for furan-HCl and furan-CHCl_3 complexes 总被引:2,自引:2,他引:0
The importance of intermolecular interactions in biology and material science has prompted chemists to explore the nature of the variety of such interactions. The strongest of these interac-tions are the hydrogen bonds, which play an important role in determining the molecular confor-mation, crystal packing, and the structure of biological systems such as nucleic acids. Extensive experimental and theoretical efforts[1—5] have been devoted to the studies of this type of interac-tions, such as … 相似文献
14.
Gas-phase 21Ne nuclear magnetic resonance spectra were measured at the natural abundance of 21Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B0 = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon. The resonance frequency was extrapolated to the zero-density point, and it permitted the determination of the 21Ne nuclear magnetic moment, μ(21Ne) = 0.6617774(10) μN. The present value of μ(21Ne) is not influenced by the bulk magnetic susceptibility of neon and interactions between neon atoms; therefore, it is more precise and reliable than the previous result obtained for μ(21Ne). 相似文献
15.
McDowell SA 《The Journal of chemical physics》2004,120(8):3630-3634
Stable linear weakly bound hydrogen-bonded complexes of HArF and HKrF with the CO molecule have been predicted by ab initio computations at the MP2/6- 311+ +G(2d,2p) level of theory. The complexes, having stabilities in the order, FArH...CO>FKrH...CO>FArH...OC>FKrH...OC are compared. They exhibit unusual blueshifts of the Ar-H (Kr-H) stretching frequency, as well as contraction of the Ar-H (Kr-H) bond, and these effects are rationalized mainly in terms of shifts in the electron density of HArF (HKrF) on complexation, caused mainly by a combination of the intermolecular electrostatic interaction, electron-electron (Pauli) and nuclear-nuclear repulsion and charge density transferred from the CO molecule to the rare-gas-containing molecule. 相似文献
16.
17.
Grabowski SJ 《The journal of physical chemistry. A》2011,115(45):12789-12799
MP2/6-311++G(3pd,3df) calculations were performed on complexes of acetylene and fluoroform acting as the proton donating systems and different Lewis bases being the proton acceptors since these complexes are linked through C-H···Y hydrogen bonds. Quantum Theory of Atoms in Molecules (QTAIM) is applied to explain the nature of these interactions. The characteristics of bond critical points are presented for these complexes. The inter-relations between energetic and geometrical parameters as well as the parameters derived from the Natural Bond Orbital (NBO) theory are analyzed here. Red- and blue-shifted hydrogen bonds are detected for the complexes investigated and the differences between those interactions are analyzed from the QTAIM perspective. It is shown that such differences are in agreement with the Bent rule. The position of the bond critical point of the proton donating bond is connected with the nature of hydrogen bonding, that is, if it is blue- or red-shifted. 相似文献
18.
Novel Dimethinemerocyanine Dyes with the (Sulfobutyl)benzothiazole Group as Donor Part of the Chromophor and their Aggregation Tendency in Aqueous Solution A series of novel dimethinemerocyanine dyes with the (sulfobutyl)benzothiazole group as the donor part of the chromophor is synthesized in good yield and their aggregation tendency in H2O without addition of salt investigated. The merocyanine dye 2b only gives J-aggregation in H2O. The dyes 1a–f and 2a exhibit an intense, red-shifted absorption band due to J-aggregation in H2O in the presence of Me4NCl. In contrast, the dyes 1g and 2c–f show a slightly red-shifted absorption band. The degree of aggregation in H2O is investigated by ultracentrifugation of the representative 2e . Indeed, the slightly red-shifted absorption band in H2O is due to aggregation of ‘oligomers’ of the dye. Contrary to the aggregation of ‘polymers’ of dyes (J-aggregation), we suggest the term ‘K’ band for the slightly red-shifted absorption band. The hemicyanine dye 5 gives the same absorption band in MeOH and in MeOH/H2O 1:3. The dye 11 shows an absorption band in H2O that is probably blue-shifted because of negative solvatochromism. The merocyanine dye 13 gives H-aggregation in H2O. 相似文献
19.
The stability and geometrical structure of the fluoronium ion is investigated using the onedeterminant SCF LCAO MO method. The equilibrium geometry is characterized by a bond length of d(FH)=0.95 Å and a bond angle of 114.75°. The proton binding energy is determined to be 120.1 kcal/mole. The molecules FH
3
2+
and FH3 are found to be unstable. A binding energy of 30.7 kcal/mole is obtained for the hydrogen bond formation between the systems FH
2
+
and FH. In the minimum energy structure the central proton is situated midway between the two F atoms in a symmetrical single minimum potential. The general behavior of the potential curves of the di-solvated proton involving NH3, OH2, and FH as solvent molecules is discussed. In all these cases double minimum potentials are found, if the equilibrium separation between the heavy atoms is larger than approximately 2.4 Å, and single minimum potential for separations smaller than this value. 相似文献
20.
Cher Ling Toh Jianwei Xu Xuehong Lu Chaobin He 《Journal of polymer science. Part A, Polymer chemistry》2005,43(20):4731-4743
Two series of difunctional proton acceptors, stilbazole derivatives 4a – c and 6a – c with different spacers, oligo(methylene) and oligo(ethylene glycol), respectively, were synthesized. Hydrogen‐bonded polymeric complexes 4 / 7 and 6 / 7 and trimeric complexes 4 / 82 and 6 / 82 ( 7 and 8 are aromatic dicarboxylic acids and monocarboxylic acids, respectively) were prepared, and their liquid crystallinity was examined. The effects of the spacer in 4 , 6 , and 7 and the terminal group in 8 on the thermal behaviors of hydrogen‐bonded complexes were investigated using differential scanning calorimetry and polarizing optical microscopy. X‐ray diffraction at elevated temperatures was used to verify liquid crystal phases. The study showed that the phase transition temperatures for isotropic to nematic (TI–Ns) of polymeric complexes 4 / 7 and 6 / 7 in general decreased with the increase in length of spacer in the corresponding proton donors 7 . The increase in length of the proton acceptors 6 led to a drop of TI–Ns of the corresponding complexes 6 / 7 ; however, the TI–Ns of complexes 4 / 7 did not show any correlation with the spacer length in 4 . In contrast, the increase in length of the terminal group in 8 resulted in a slight decrease in TI–Ns of trimeric complexes 4 / 82 , but had a negligible effect on the TI–Ns of 6 / 82 because of the presence of the more flexible spacer in the proton acceptors 6 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4731–4743, 2005 相似文献