Indirect 1H NMR characterization of H2@C60 nitroxide derivatives and their nuclear spin relaxation

(1)H NMR of two H(2)@C(60) nitroxide derivatives has been characterized indirectly by reducing to their corresponding hydroxylamines. Nuclear spin relaxation of the endohedral H(2) and external protons of the H(2)@C(60) nitroxide and its corresponding hydroxylamine were measured and analyzed. The observed spectra are consistent with negligible scalar coupling between the unpaired electron and the endo-H(2). An unexpectedly large bimolecular relaxivity induced in the hydroxylamine by the corresponding nitroxide can be explained by rapid hydrogen atom transfer between the two species.     

Synthesis and structural characterization of endohedral pyrrolidinodimetallofullerene: La2@C80(CH2)2NTrt

The endohedral pyrrolidinodimetallofullerene, La2@C80(CH2)2NTrt (Trt = triphenylmethyl), was successfully synthesized and characterized. X-ray crystallographic and NMR spectroscopic analyses reveal that two La atoms in the 6,6-adduct are localized at the stable site on the mirror plane. Theoretical calculation also suggests the localization of two La atoms in the 6,6-adduct.     

Structural elucidation of a new delta2-pyrazoline derivatives using 1H and 13C NMR spectroscopy

This paper describes the unequivocal structural elucidation of a new kind of Delta2-pyrazoline derivatives carried out by means of monodimensional 1H and 13C NMR spectroscopies, bidimensional ones such as HMBC and HMQC experiments, and NOEDIFF effects. Conformational analysis of this molecule agrees very well with the experimentally NOEDIFF effects found.     

Synthesis, NMR characterization and reactivity of 1-silacyclohex-2-ene derivatives

The chloro functionality of allyldichlorosilane (HSiCl₂(C₃H₅)) and allyldichloromethylsilane (MeSiCl₂(C₃H₅)) were replaced by alkynyl groups and new compounds, allyldialkynylsilane 1 and allyldialkynylmethylsilane 2, were obtained. These silanes, which served as starting materials for the onward reactions, were purified by fractional distillation. They were further subjected to hydroboration with 9-BBN (9-borabicyclo[3.3.1]nonane) and were converted into 1-silacyclohex-2-ene derivatives 5 and 6. The competition between C≡C and C=C in the reaction was studied. The hydroborating reagent 9-BBN was expected to prefer terminal C=C bonds and to leave C≡C bond untouched. This hypothesis of preferable hydroboration was experimentally proved, and hence, 1-silacyclohex-2-ene derivatives were obtained in reasonably pure form. The reaction of allyldialkynylsilane 2 with one equivalent of 9-BBN affords 1-silacyclohex-2-ene bearing Si-C≡C-function, ready to be hydroborated further with one equivalent of 9-BBN. The obtained compound bears two C-B bonds, which are attractive synthones for further transformations. This study aims to highlight the chemistry of C-B and Si-H functional groups. All new compounds obtained were colorless air and moisture sensitive oils, and they were studied by multinuclear magnetic resonance spectroscopy (¹H, ¹³C, ¹¹B, ²⁹Si NMR) in solution.      

Synthesis and characterization of tetrakis-silylated C60 isomers

A photochemical reaction of C(60) with disilane in a 2:3 ratio affords the isomer mixture of the tetrakis-adduct of C(60)((t)BuPh(2)Si)(4) as the major product. The use of a three-stage HPLC separation system isolated three of their isomers. Their structural assignments were based on FAB mass, UV-vis, NMR, and cyclic voltammetry (CV) measurements. The CV analysis showed that the terakis-adduct has lower oxidation and higher reduction potentials than the bis-adduct C(60)((t)BuPh(2)Si)(2) and the parent C(60).     

Nuclear relaxation of H2 and H2@C60 in organic solvents

The 1H nuclear spin-lattice relaxation time (T1) of H2 and H2@C60 in organic solvents varies with solvent, and it varies proportionally for H2 and for H2@C60. Since intermolecular magnetic interactions are ruled out, the solvent must influence the modulating processes of the relaxation mechanisms of H2 both in the solvent cage and inside C60. The temperature dependence of T1 also is very similar for H2 and H2@C60, T1 going through a maximum by varying the temperature in solvents which allow a wide range of temperatures to be explored. This behavior is attributed to the presence of dipolar and spin-rotation mechanisms which have an opposite dependence on temperature.     

Infrared spectroscopy of endohedral HD and D2 in C60

We report on the dynamics of two hydrogen isotopomers, D(2) and HD, trapped in the molecular cages of a fullerene C(60) molecule. We measured the infrared spectra and analyzed them using a spherical potential for a vibrating rotor. The potential, vibration-rotation Hamiltonian, and dipole moment parameters are compared with previously studied H(2)@C(60) parameters [M. Ge, U. Nagel, D. Hüvonen, T. R??m, S. Mamone, M. H. Levitt, M. Carravetta, Y. Murata, K. Komatsu, J. Y.-C. Chen, and N. J. Turro, J. Chem. Phys. 134, 054507 (2011)]. The isotropic part of the potential is similar for all three isotopomers. In HD@C(60), we observe mixing of the rotational states and an interference effect of the dipole moment terms due to the displacement of the HD rotation center from the fullerene cage center.     

Synthesis and NMR spectroscopic characterization of Si-substituted 1-silacyclobutene derivatives

Hydroboration of trialkyn-1-yl(organo)silanes with one equivalent and two equivalents of 9-borabicyclo[3.3.1]nonane, 9-BBN afford dialkyn-1-ylsilanes and alkyn-1-ylsilanes, respectively. The alkyn-1-ylsilane derivatives are stable at room temperature and can be store under dry argon for prolong period of time. These compounds are attractive materials for further rearrangements to afford novel 1-silacyclobutene derivatives bearing Si-alkenyl or Si-alkynyl functionalities. The hydroboration reaction is well controlled by the Si-R¹ function, i.e., the starting silanes with R¹ = Ph selectively afford hydroboration of one Si-C≡C bond with one equivalent of 9-BBN, leaving the other two functionalities untouched. Under mild reaction conditions (25°C), the starting silanes with R¹ = Me lead to mixture containing dialkyn-1-ylsilane, alkyn-1-ylsilane and their respective 1-silacyclobutene derivatives. All new compounds are sensitive towards air and moisture and were studied by multinuclear magnetic resonance spectroscopy (¹H, ¹³C, ¹¹B, ²⁹Si NMR) in solution.     

Synthesis and1H NMR and13C spectroscopy of L-arabinopyranosyl biosides

Conclusions The 3-0- and 4-0-trityl ethers of the acetates of methyl -L- arid methyl -L-arabinopyranosides were synthesized. The glycosylation of the ethers with the aid of 3,4-di-0-acetyl-1,2-0-(1-exo-cyano)ethylidene--L-arabinopyranose and the subsequent deacetylation of the synthesized products yielded the disaccharides: methyl 4-0-(-L-arabinopyranosyl)-,methyl 4-0-(-L-arabinopyranosyl)-, and methyl 3-0-(-L-arabinopyranosyl)--L-arabinopyranoside; and methyl 4-0-(-L-arabinopyranosyl)-, methyl 4-0-(-L-arabinopyranosyl)-, methyl 3-0-(-L-arabinopyranosyl)-, and methyl 3-0-(-L-arabinopyranosyl)--L-arabinopyranoside.The assignment of the signals in the PMR and¹³C NMR spectra of the synthesized arabinopyranosyl biosides was carried out, allowing the determination of the type and configuration of the glycosidic bond by means of which the arabinopyranose residues are linked in the oligo- and polysaccharide chains.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 200–209, January, 1986.     

Measurements of heavy-atom isotope effects using 1H NMR spectroscopy

A novel method for measuring heavy-atom KIEs for magnetically active isotopes using (1)H NMR is presented. It takes advantage of the resonance split of the protons coupled with the heavy atom in the (1)H spectrum. The method is validated by the example of the (13)C-KIE on the hydroamination of styrene with aniline, catalyzed by phosphine-ligated palladium triflates.     

Establishment of the configuration of derivatives of 2Z-butene-1,4-diol by1H NMR spectroscopy

¹H NMR spectroscopy and the PANIC program for obtaining calculated spectra were used to show that the Z-configuration of the C=C bond is retained in the conversions of 2Z-butene-1,4-diol to the corresponding monobromide and monochloride and in the reaction of this monobromide with amylmagnesium bromide in the presence of the Kochi reagent (Li₂CuCl₄) and with the tert-butylimine of acetaldehyde.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1180–1182, May, 1990.     

Synthesis and1H NMR study of some organotin derivatives of diethanolamines

A number of organotin derivatives of diethanolamines (stannocanes) R₂Sn(OCH₂CH₂)₂NR', O(SiMe₂CH₂)₂Sn(OCH₂CH₂)₂NR', and Sn[(OCH₂CH₂)₂NR']₂ (R = Ph,cyclo-Hex; R' = H, Me, Ph) were synthesized and studied by¹H NMR spectroscopy. The effect of steric factors on the ability of molecules of stannocanes to form associates in solutions is discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp.714–718, April, 1994.     

Synthesis and structure elucidation of five new conjugates of oleanolic acid derivatives and chalcones using 1D and 2D NMR spectroscopy

Five new conjugates of oleanolic acid derivatives and chalcones have been designed and synthesized. The structure elucidation of these conjugates was accomplished by using extensive 1D (¹H, ¹³C) and 2D NMR spectroscopic studies (COSY, HSQC and HMBC); and α‐glucosidase inhibitory activity is reported for these conjugates. Compound 2b (IC₅₀ = 47.5 µm ) displayed much stronger activity than oleanolic acid and acarbose. Copyright © 2012 John Wiley & Sons, Ltd.     

Interaction potential and infrared absorption of endohedral H2 in C60

We have measured the temperature dependence of the infrared spectra of a hydrogen molecule trapped inside a C(60) cage, H(2)@C(60), in the temperature range from 6 to 300 K and analyzed the excitation spectrum by using a five-dimensional model of a vibrating rotor in a spherical potential. The electric dipole moment is induced by the translational motion of endohedral H(2) and gives rise to an infrared absorption process where one translational quantum is created or annihilated, ΔN = ±1. Some fundamental transitions, ΔN = 0, are observed as well. The rotation of endohedral H(2) is unhindered but coupled to the translational motion. The isotropic and translation-rotation coupling part of the potential are anharmonic and different in the ground and excited vibrational states of H(2). The vibrational frequency and the rotational constant of endohedral H(2) are smaller than those of H(2) in the gas phase. The assignment of lines to ortho- and para-H(2) is confirmed by measuring spectra of a para enriched sample of H(2)@C(60) and is consistent with the earlier interpretation of the low temperature infrared spectra [Mamone et al., J. Chem. Phys. 130, 081103 (2009)].     

Paramagnet enhanced nuclear relaxation of H2 in organic solvents and in H2@C60

We have measured the bimolecular contribution (relaxivity) R1 (M(-1) s(-1)) to the spin-lattice relaxation rate for the protons of H2 and H2@C60 dissolved in organic solvents in the presence of paramagnet nitroxide radicals. It is found that the relaxation effect of the paramagnets is enhanced 5-fold in H2@C60 compared to H2 under the same conditions. 13C relaxivity in C60 induced by nitroxide has also been measured. The resulting value of R1 for 13C is substantially smaller relative to the 1H relaxation in H2@C60 than expected solely on the basis of the smaller magnetic moment of 13C. The observed values of R1 have been analyzed quantitatively using an outer-sphere model for bimolecular spin relaxation to extract an encounter distance, d, as the dependent variable. The resulting values of d for H2 and (13)C60 are similar to the sum of the van der Waals radii for the radical and the corresponding molecule. The value of d for (1)H2@C60 is substantially smaller than the corresponding van der Waals estimates, corresponding to larger than expected values of R1. A possible explanation for the enhanced relaxivity is a contribution from hyperfine coupling. Based on the results reported here, it seems that not only is the hydrogen molecule in H2@C60 not insulated from magnetic contact with the outside world but also the interaction with paramagnets is even stronger than expected based on distance alone.     

Separation of N2@C60 and N@C60

We describe the HPLC separation and identification of N@C60 and N2@C60. These species were observed after eleven sequential HPLC separations. Their retention times are in the same range as those of the other noninteractive endohedral species of C60, such as noble gas endohedral C60. The separation factors of these endohedrals were evaluated by using a mixture of hexane/toluene as eluent. We note that this is the first evidence for the N2@C60 molecule existing in the form of endohedral C60 complex.