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The reliability of the continuous transformations of origin of the current density method, which makes the transverse paramagnetic current vanish (CTOCD-PZ), for the prediction of nearly gauge-origin independent molecular magnetic susceptibility and gauge-origin independent nuclear magnetic shielding, is proved on the basis of a fairly large number of calculations. It is shown that, within the computational scheme provided by the coupled Hartree–Fock perturbation theory (CHF), convergence towards the presumed Hartree–Fock limit, for magnetic susceptibility and proton magnetic shielding, is systematically reached using basis sets which are smaller than those required by conventional common origin and CTOCD-DZ techniques. For second-row nuclear magnetic shieldings a variant of the CTOCD-PZ method, which shifts the origin of the current towards the nearest nucleus for points close to nuclei, as suggested originally by Keith and Bader with the CSDGT method [T. A. Keith and R. F. W. Bader, Chem. Phys. Lett. 210, 223 (1993)], gives likewise good results with affordable basis sets.

Articles you may be interested inNon-perturbative calculation of molecular magnetic properties within current-density functional theory Gauge invariant calculations of nuclear magnetic shielding constants using the continuous transformation of the origin of the current density approach. II. Density functional and coupled cluster theory J. Chem. Phys. 126, 154111 (2007); 10.1063/1.2721536Correlated and gauge invariant calculations of nuclear magnetic shielding constants using the continuous transformation of the origin of the current density approach Calculation of third-rank molecular hypermagnetizabilities by continuous transformation of the origin of the current density Coupled Hartree-Fock calculations of molecular magnetic properties annihilating the transverse paramagnetic current density A new method for the calculation of molecular magnetic susceptibility and nuclear magnetic shielding is presented. It is based on continuous transformations of origin of the current density which make the transverse part of the paramagnetic current vanish. For any molecule all the components of the nuclear magnetic shielding tensor provided by the new method are independent on the origin of the gauge, whereas the components of the magnetizability tensor are translationally invariant only for center-symmetric molecules ͑they, in general, show a linear dependence on the shift of origin͒. This method, termed CTOCD-PZ, has been implemented for the theoretical determination of molecular magnetic properties via numerical integration techniques and, from preliminar results obtained for methane and carbon dioxide molecules, reveals reliable.

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In this paper, both Hartree-Fock (HF) and density functional theory (DFT) methods have been used to make ab initio calculations of the optical rotatory power of selected molecules at several wavelengths; that is, part of the optical rotatory dispersion (ORD) curve has been predicted. This approach constitutes a new, simple, and reliable method to assign the molecular absolute configuration, at least for rigid molecules such as those studied in the present work. In fact, in this way, it is possible to overcome the difficulties connected to some relevant cases, in particular that of (-)-beta-pinene, for which even a very high-level (DFT/B3LYP/6-311++G(2d,2p)) calculation affords the wrong sign of the optical rotation at 633 nm. On the contrary, the predicted ORD curve, even using small basis sets, reproduces (below 400 nm) the experimental trend well, allowing for the correct configurational assignment. This result clearly shows that to have a reliable configurational assignment the comparison between experimental and predicted rotation values must be carried out at different wavelengths and not at a single frequency. The reason for this is that working at wavelengths approaching the absorption maximum the [alpha](lambda) values become larger and their prediction becomes more reliable. Coupling the use of an inexpensive instrument (a polarimeter working at a few wavelengths) with the use of a DFT-calculation package can also allow the experimental organic chemist to arrive, quickly and reliably, at the assignment of the molecular absolute configuration.

By partitioning the bond current strength (current susceptibility) into plane symmetric and plane antisymmetric contributions, it is shown that 91% of the diatropic ring current of benzene is transported by the π electrons and the remaining non-negligible 9% is sustained by the σ electrons. In planar cyclooctatetraene 94% (6%) of the paratropic ring current is transported by the π (σ) electrons. In cyclopropane 95% (5%) of the diatropic ring current is transported by the σ (π-like) electrons. The 85% fraction of the diatropic ring current of Al4(2-) is transported by the σ valence electrons and 15% by the π valence electrons. In the nonaromatic borazine system the nitrogen-centered π electron circulations are surrounded by a weak diatropic "ring current" 6.5 times smaller than that of benzene.

In this study, the systemic assessments of the stereoisomers of triazole fungicide difenoconazole are reported for the first time, including absolute stereochemistry, stereoselective bioactivity toward pathogens (Alternaria sonali, Fulvia fulva, Botrytis cinerea, and Rhizoctonia solani), and toxicity toward aquatic organisms (Scenedesmus obliquus, Daphnia magna, and Danio rerio). Moreover, the stereoselective degradation of difenoconazole in vegetables (cucumber, Cucumis sativus and tomato, Lycopersicon esculentum) under field conditions and in soil under laboratory-controlled conditions (aerobic and anaerobic) was investigated. There were 1.33-24.2-fold and 1.04-6.78-fold differences in bioactivity and toxicity, respectively. Investigations on the stereoselective degradation of difenoconazole in vegetables showed that the highest-toxic and lowest-bioactive (2S,4S)-stereoisomer displays a different enrichment behavior in different plant species. Under aerobic or anaerobic conditions, (2R,4R)- and (2R,4S)-difenoconazole were preferentially degraded in the soil. Moreover, difenoconazole was configurationally stable in the test soil matrices. On the basis of biological activity, ecotoxicity, and environmental behavior, it is likely that the use of pure (2R,4S)-difenoconazole instead of the commercial stereoisomer mix may help to increase the bioactivity and reduce environmental pollution.

Both the ab initio expression of the current density within the ipsocentric approach and conjugated circuit models indicate that placing an unsaturated hydrocarbon inside a [4n]annulene, in such a way that outgoing C-H bonds are substituted by C-C bonds to alternating carbon atoms of the annulene, leads to an homologue altan-molecule whose perimeter is expected to preserve the paratropic circulation of the parent annulene. Computations of current on the novel altan-corannulene and altan-coronene revealed unprecedented patterns of three contra-rotating paratropic/diatropic/paratropic circulations. Graph-theoretical methods have been used to highlight the peculiar topology of these altan-molecules.