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1.
The hybridization in several cyclic polyacetylene compounds has been calculated by the maximum overlap method, assuming planar and non-planar geometries of the molecules. In the planar configuration the hybrids describing the molecular skeleton deviate from the corresponding bond directions. We have a few “bent” bonds, but in contrast to the situation in small rings, here the deviation angles are negative, i.e., the hybrids point toward the inside of the ring. Non-planar structures in which acetylene groups are kept in a plane and CCH2 or CH2 groups are displaced out of the plane show less deviation from the bond directions of bent bonds. Furthermore, the deviation angles decrease with an increase in the out-of-plane displacement of methylene groups. Finally, when the angle of bending of the molecules approaches 50°, the deviation vanishes, predicting a puckered conformation for the molecules. Correlation between CC stretching vibration frequencies and the corresponding CC bond overlap is discussed. 相似文献
2.
Denize C. Favaro Rubén H. Contreras Cláudio F. Tormena 《Magnetic resonance in chemistry : MRC》2013,51(6):334-338
SOPPA(CCSD) calculations show that the FC term is the most important contribution to the through‐space transmission of JFN coupling constants for the fluoroximes studied in this work. Because of the well‐known behavior of FC term, a new rationalization for the experimental TSJFN SSCC is presented. It is mainly based on the overlap matrix (Sij) between fluorine and nitrogen lone pairs obtained from NBO analyses. An expression is proposed to take into account the influence of the electronic density (Dij) between coupled nuclei as well as the s% character at the site of the coupling nuclei of bonds and non‐bonding electron pairs involved in Dij. In using this approach, a linear correlation between TSJFN versus Dij is obtained. The most important aspect of this rationalization is related to the facility for understanding the behavior of some unusual experimental coupling constants. It is shown that, at least in this case, the electronic origin of the so‐called through‐space coupling is transmitted through to the overlap of orbitals on the coupled atoms, suggesting that, at least for these compounds, instead of through‐space coupling, it should better be dubbed as ‘through overlapping orbital coupling’. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
3.
Rubén Marín-Barrios Francisco M. Guerra Ana Leticia García-Cabeza F. Javier Moreno-Dorado Guillermo M. Massanet 《Tetrahedron》2012,68(4):1105-1108
The multivariate optimization method known as simplex is applied to the Kharasch–Sosnovsky allylic oxidation of double bonds. By applying this method, the amounts of three variables (copper source, oxidant, and additive) are optimized at the same time. Under the conditions thus obtained the reaction takes place in a considerable shorter time, being the alkene the limiting reagent. These conditions are applied to some monoterpenes and sesquiterpenes leading regioselectively to the corresponding benzoate esters, opening a route to the employment of this reaction in the synthesis of more complex molecules. 相似文献
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5.
Naved Azum Malik Abdul Rub Abdullah M. Asiri Mohd. Akram 《Russian Journal of Physical Chemistry B, Focus on Physics》2015,9(6):940-945
Aggregation behavior of cationic gemini (hexanediyl-1,5-bis(dimethylcettylammonium bromide) (16-5-16)) surfactant with conventional single chain surfactants cetyltrimethylammonium bromide (CTAB) and tetradecyltrimethylammonium bromide (TTAB) were studied with the help of fluorescence measurements. Fluorescence probe is a proficient technique for examining the surfactant-surfactant interaction and aggregation. The micelle aggregation number (N agg) was measured using steady-state fluorescence quenching method. The micelle aggregation numbers of binary combinations fall between those of constituent surfactants. The micropolarity (I 1/I 3), binding constant (K sv) and dielectric constant (D exp) of mixed systems were determined from the ratio of peaks intensity in the pyrene fluorescence spectrum. The I 1/I 3 values were found to be more than >1, showing more polar environment around pyrene in the mixed micelle as compared to the pure micelles. 相似文献
6.
Mixtures of antidepressant amphiphilic drug imipramine hydrochloride and anionic surfactant: Micellar and thermodynamic investigation 下载免费PDF全文
Farah Khan Malik Abdul Rub Naved Azum Abdullah M. Asiri 《Journal of Physical Organic Chemistry》2018,31(6)
Aggregation as well as thermodynamic behavior of amphiphilic imipramine hydrochloride (IMH) drug (antidepressant) and anionic surfactant (sodium dodecyl sulfate [NaDS] as well as sodium dodecylbenzenesulfonate [NaDBS]) mixtures as a function of solution composition in aqueous solutions have been evaluated by conductometry method at different temperatures. Surfactant (NaDS and NaDBS) employed in the current study is anionic in nature. Various theoretical models such as Clint, Rubingh, Motomura, and Rodenas were employed to gain information regarding the type of interaction between the components in the solution mixtures. The value of micellar mole fraction evaluated by different utilized models is found to be more for IMH‐NaDBS mixtures in comparison with IMH‐NaDS mixtures, signifying that participation of NaDBS is more in mixed micelles as compared with NaDS. Owing to the different charge of employed drug and surfactant, which sources high synergistic results in the mixed system comparative to the possessions of their pure compounds, means here anionic surfactants were elected in favor of the quantitation of cationic drug. The value of interaction parameters (β) was also evaluated by employing the Rubingh's model. The values of Gibbs free energy (?G0m) for all systems attained to be negative in all studied systems showing that the systems are spontaneous in nature. 相似文献
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Nonlinear Dynamics - Delay-coordinate maps have been widely used recently to study nonlinear dynamical systems, where there is only access to the time series of one of their variables. Here, we... 相似文献
9.
Martínez-Martín D Jaafar M Pérez R Gómez-Herrero J Asenjo A 《Physical review letters》2010,105(25):257203
In this work we investigate possible ferromagnetic order on the graphite surface by using magnetic force microscopy (MFM). Our data show that the tip-sample interaction along the steps is independent of an external magnetic field. Moreover, by combining kelvin probe force microscopy and MFM, we are able to separate the electrostatic and magnetic interactions along the steps obtaining an upper bound for the magnetic force gradient of 16 μN/m. Our experiments suggest the absence of ferromagnetic signal in graphite at room temperature. 相似文献
10.
Highly Enantioselective Construction of Tricyclic Derivatives by the Desymmetrization of Cyclohexadienones 下载免费PDF全文
Sandra del Pozo Dr. Alejandro Parra Dr. Sergio Díaz‐Tendero Dr. Rubén Mas‐Ballesté Dr. Silvia Cabrera Dr. José Alemán 《Angewandte Chemie (International ed. in English)》2014,53(31):8184-8189
The asymmetric synthesis of tricyclic compounds by the desymmetrization of cyclohexadienones is presented. The reaction tolerated a large variety of substituents at different positions of the cyclohexadienone, and heterocyclic rings of different sizes were accessible. Density functional theory calculations showed that the reaction proceeds through an asynchronous [4+2] cycloaddition. 相似文献