Acta Crystallogr Sect E Struct Rep Online
January 2010
The crystal structure of the title compound, C(11)H(18)O(6)S(2), was determined to investigate the effect of the eclipsed mesyl groups on the bond length of the vicinal quaternary C atoms. The two quaternary C atoms of the noradamantane skeleton and the two O atoms to which they are connected all located essentially in the same plane [maximum deviation 0.01 Å], resulting in an eclipsing conformation of the C-O bonds.
View Article and Find Full Text PDF[reaction: see text] Attempts to isolate the (Ph(3)P)(2)Pt complex of the highly pyramidalized olefin 3,7-dimethyltricyclo[3.3.0.
View Article and Find Full Text PDF[reaction: see text] Computations find that o-phenylene(halo)carbenonitrenes 2-XN, X = F, Cl, Br, have quinoidal singlet biradical ground states such as the parent o-phenylenecarbenonitrene (2-HN). Compared to the parent 2-HN, halogen substitution stabilizes the A'' states relative to the A' ones. Halogen substitution also affects the barrier and exothermicity of the ring-opening reaction (to form unsaturated nitriles 4-XN, X = F, Cl, Br), but it has a smaller effect on the ring-closing reaction (to form benzo(aza)cyclobutadiene 3-XN, X = F, Cl, Br).
View Article and Find Full Text PDFPhotolysis of the cryptand 1, bearing an intraannular azido substituent, results in a complex photochemistry. Low-temperature photolysis yields the triplet nitrene (3)2, which has been characterized by EPR spectroscopy. Small differences in ZFS parameters are detected between the uncomplexed nitrene-functionalized ligand (in EtOH: D' = 0.
View Article and Find Full Text PDFA prerequisite for a stable singlet hydrocarbon carbene is the existence of high barriers toward isomerization. Four derivatives of cyclopentylidene (1-4) with rigid and varying carbon cages are examined computationally at the B3LYP/6-311+G(d,p) level of theory. Singlet ground states are predicted for carbenes 1-4, with DeltaE(ST)'s = 7-22 kcal/mol.
View Article and Find Full Text PDFm-Phenylene-coupled carbenonitrenes [(3-nitrenophenyl)methylene (2-H), (3-nitrenophenyl)fluoromethylene (2-F), (3-nitrenophenyl)chloromethylene (2-Cl), (3-nitrenophenyl)bromomethylene (2-Br)] have been investigated computationally (with B3LYP, MCSCF, CASPT2, ROMP2, and QCISD(T) methods) and experimentally (with IR, UV, and ESR spectroscopy). For each species, five electronic states were considered. At the highest level of theory explored, the parent compound (2-H) has a quintet ground state, but its halogen derivatives (2-X, X = F, Cl, and Br) have triplet ground states.
View Article and Find Full Text PDFThe singlet and triplet states of cyclobutenylidene, cyclopenten-3-ylidene, cyclohexen-3-ylidene, and cyclohepten-3-ylidene and some of their isomers (cyclohexen-4-ylidene, cyclohepten-4-ylidene, and cyclohepten-5-ylidene) have been studied computationally (using ab initio and DFT methods) in order to assess the effect of angle strain on the S-T gap of small- and medium-size cyclic alkenylidenes. Ground-state intramolecular rearrangements of the conjugated cycloalkelnylidenes have also been examined with an emphasis on the smaller four-membered ring, which is compared to its higher homologues. It is found that cyclobutenylidene has a singlet ground state and a significant singlet-triplet gap (25 kcal mol(-)(1)).
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