Arthur R. Tulyabaev

Homo‐ and methano[60]fullerenes with chiral attached moieties – 1H and 13C NMR chemical shift assignments and diastereotopicity effects

1H and 13C NMR chemical shift predictions of homo‐ and methano[60]fullerenes containing chiral centers in attached fragment were made using the two‐dimensional NMR technique (HH COSY, 1H–13C HSQC and HMBC) and the quantum chemistry GIAO calculation method in the PBE/3ζ approach. The influence of a chiral substituent on the 13C chemical shifts of diastereotopic fullerene carbons was estimated by comparing the calculated and experimental 13C NMR spectra. The resonances of the fullerene carbons in α‐, β‐ and δ‐positions relative to the position of the substituent exhibit the greatest diastereotopic splitting. Copyright

Diastereotopic splitting in the 13C NMR spectra of sulfur homofullerenes and methanofullerenes with chiral fragments.

Using gauge‐invariant atomic orbital PBE/3ζ quantum chemistry approach, 13C NMR chemical shifts and diastereotopic splittings of sp2 fullerenyl carbons of a number of sulfur homofullerenes and methanofullerenes have been predicted and discussed. An anisochrony of fullerene carbons is caused by a chiral center of attached moieties. Clearly distinguishable diastereotopic pairs (from 8 to 11) of fullerenyl carbons of homofullerenes were observed. Unambiguous assignments of 13C NMR chemical shifts were performed, and diastereotopic splittings of methanofullerenes were observed for α, β and γ to a functionalization site. Copyright

Intermolecular interactions and chiral crystallization effects in (1,5,3-dithiazepan-3-yl)-alkanoic acids

Crystals of (1,5,3-dithiazepan-3-yl)-alkanoic acids with achiral and chiral amino acid moieties have been obtained, and their structures were studied using a single crystal X-ray technique. Simple crystal systems, namely monoclinic, triclinic, and orthorhombic, were revealed in a series of the studied compounds. The reference 1,5,3-dithiazepan-3-ol forms head-to-head cyclic dimeric associates R22(6) via strong O–H⋯N intermolecular hydrogen bonds. The achiral 1,5,3-dithiazepanes form head-to-head cyclic dimers R22(8) between two carboxylic groups, whereas the co-crystals involve solvent molecules to constitute dimeric pairs R33(11) and R22(8) through O⋯H and N⋯H hydrogen bonds. These dimers further contribute to the aggregation of layers and stacks due to diverse H⋯H and S⋯H contacts. The chiral dithiazepanes form head-to-tail R12(6), R22(7), and R22(8) cyclic dimers between the carboxylic group of one molecule and the dithiazepane moiety of the other one through H⋯H, S⋯H, and O⋯H intermolecular contacts. Hirshfeld analysis has shown that S⋯H (9.2–19.8%) and O⋯H (5.4–18.2%) intermolecular hydrogen bonds as well as weak H⋯H contacts (40.2–64.0%) are predominant in all the compounds to form crystal packing.

Neural network for prediction of 13C NMR chemical shifts of fullerene C60 mono‐adducts

Real‐valued models based on deep artificial neural networks were proposed to predict 13C NMR chemical shifts of fullerene C60 core carbon atoms for computer‐aided structure elucidation of complex fullerene C60 mono‐adducts. We showed that parametric rectified linear units could be successfully used as activation functions in hidden layers of artificial neural networks for decision of complex physical‐chemical tasks. A total of 400 artificial neural networks were trained and tested in order to reveal the best‐fitted models. The best prediction accuracy of real‐valued models was achieved with MAEP = 1.83 ppm/RMSEP = 2.60 ppm using artificial neural network model which has 110 and 120 hidden units, respectively, with parametric rectified linear unit as activation function.

What is responsible for conformational diversity in single-crystal tetraoxazaspiroalkanes? X-Ray, DFT, and AIM approaches

The conformational mobility of large heteroatomic cycles (>6) in organic compounds studied in the liquid state is a major challenge. This is due to low energy barriers between the conformational isomers (1–2 kcal mol−1), which make it difficult to find the most important factors in their preference. Eleven single crystal tetraoxazaspirocycloalkanes are considered in this work with single-crystal X-ray diffraction, DFT, and AIM calculations. Natural bond orbital analysis at the B3LYP/6-31G(d,2p) level of theory and topological analysis of the electron density within Baders theory of “Atoms in Molecules” showed that the tetraoxazocane cycle in spiro-adamantanetetraoxazocanes and tetraoxazaspiroalkanes possesses a twist–boat–chair conformation due to the lower interaction energy of LP(O6) → σ*(C5–N4) and the large contribution of the π-component to the C3–O2 bond. The tetraoxazocane cycle in isopropyl-methyl-tetraoxaza-spiro-tridecanes adopts a chair–chair conformation due to the higher interaction energy of LP(O6) → σ*(C5–N4) and the smaller contribution of the π-component. A key factor, which determines the large O1–O2–O6–O7 pseudo-torsion angles (102–112°) in spiro-adamantanetetraoxazocanes and tetraoxaza-spiro-alkanes, is the absence of intramolecular C–H⋯O and C–H⋯π contacts and vice versa, which provide smaller O1–O2–O6–O7 pseudo-torsion angles (0.6–4°) in isopropyl-methyl-tetraoxaza-spiro-tridecanes. The molecules of spiro-adamantanetetraoxazocanes and tetraoxazaspiroalkanes in single crystals are stabilized via C–H⋯O and C–H⋯H–C weak intermolecular interactions. The molecules of isopropyl-methyl-tetraoxaza-spiro-tridecanes are packed in crystals with C–H⋯O unusual bifurcated one-component and multicomponent contacts.