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The 13C NMR chemical shifts of fullerene C60 exo-derivatives were calculated using quantum chemical hybrid functionals combined with Pople, Dunning correlation-consistent, and def2-TZVP split valence basis sets taking into account the solvent effect (polarizable continuum model). A relationship between theoretical and experimental 13C NMR chemical shifts (CSs) is assessed quantitatively to select a functional/basis set combination. It is found that the CAM-B3LYP/6-31G and M06L/6-31G combinations have the best convergence with experimental data in modeling the 13С NMR CSs of sp3 fullerene carbon atoms in С60 derivatives, whereas X3LYP/6-31G and CAM-B3LYP/6-31G(d) in modeling the 13С NMR CSs of their sp2 fullerene carbon atoms. [ABSTRACT FROM AUTHOR]

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 Bader's 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. [ABSTRACT FROM AUTHOR]

The relationships between experimental and theoretical 13C NMR chemical shifts of a pristine fullerene C60, monoadducts from [2 + n] cycloaddition ( n = 1-3), and one [2 + 1] bis-adduct are systematically analyzed for the first time by using diverse quantum-chemical levels of theory. These levels involved B3LYP, B3PW91, B97-2, mPW1PW91, PBE1PBE, and X3LYP hybrid functionals combined with 3-21G, 6-31G, 6-31G(d), 6-31G(d,p), 6-31G(d,2p), LanL2DZ, and SDDAll basis sets. X3LYP/6-31G approach is determined to have the lowest deviations from the 13C NMR experimental data compared to the other methods for all the fullerene compounds (mean absolute error value is 0.856 ppm and root mean squared error value is 1.197 ppm). The highest deviations are characteristic for α (sp2 C2/C5/C8/C10) and β (sp2 C6/C7/C11/C12) carbon atoms relative to a functionalization site and for those (sp3 C1/C9) directly attached with a side fragment in the [2 + n] monoadducts ( n = 1-3). A probable reason of such deviation is that the approaches do not take into account a contribution of paramagnetic ring currents to 13C NMR chemical shifts. The results will be useful in design of novel fullerene derivatives and in performing unambiguous 13C NMR chemical shift assignments with modern quantum chemistry calculations. [ABSTRACT FROM AUTHOR]

Abstract: Carboalumination of 1-alkenes (1-hexene, 1-octene, 1-decene) with Et3Al in the presence of catalytic amounts of TaCl5 results in a mixture of 2-(R-substituted)- and 3-(R-substituted)-n-butylaluminums (1:1 ratio) in total yields of 75–85%. The TaCl5-catalyzed reaction of bicyclo[2.2.1]hept-2-ene, endo-tricyclo[5.2.1.02,6]deca-3,8-diene, and (exo/endo)-5-methylbicyclo[2.1.1]hept-2-ene with Et3Al leads to the formation of diethyl[2-exo-(2′-norbornylethyl)]aluminums in high yields. DFT calculations confirm the thermodynamic preference of the final exo product. The multistep reaction mechanisms for the formation of the resultant organoaluminums through tantalacyclopentanes as key intermediates are also discussed. [Copyright &y& Elsevier]

Abstract: The stereoselective carbomagnesiation reaction of bicyclo[2.2.1]hept-2-ene, endo-tricyclo[5.2.1.02,6]deca-3,8-diene, and exo–endo-5-methylbicyclo[2.1.1]hept-2-ene with EtMgX, where X = Cl or Et, occurs in the presence of catalytic amounts of TaCl5 to give chloro- and ethyl[2-exo-(2′-norbornylethyl)]magnesiums in high yields. The multistep reaction mechanism involving norbornene and ethylene through tantalacyclopentanes as key intermediates is also postulated. DFT calculations confirm the thermodynamic preference for the resulting exo product. [Copyright &y& Elsevier]