The spiropyran-merocyanine system was studied using ion mobility-mass spectrometry (IM-MS) and three major conformers were identified. Assignment of conformers is based on DFT-B3LYP energy minimized structures and collision cross-sections as light-induced changes in IM-MS. The three conformers were assigned to the spiropyran, cisoid and transoid structures.
We report through-space (TS) (19)F-(19)F coupling for ortho-fluoro-substituted Z-azobenzenes. The magnitude of the TS-coupling constant ((TS) JFF ) ranged from 2.2-5.9 Hz. Using empirical formulas reported in the literature, these coupling constants correspond to non-bonded F-F distances (dFF) of 3.0-3.5 Å. These non-bonded distances are significantly smaller than those determined by X-ray crystallography or density functional theory, which argues that simple models of (19)F-(19)F TS spin-spin coupling solely based dFF are not applicable. (1)H, (13)C and (19)F data are reported for both the E and Z isomers of ten fluorinated azobenzenes. Density functional theory [B3YLP/6-311++G(d,p)] was used to calculate (19) F chemical shifts, and the calculated values deviated 0.3-10.0 ppm compared with experimental values.
The synthesis and reactivity of a tetrahydrochromeno [2,3-b]indoles are reported. Evidence for reversible ring-opening is based on H/D exchange and trapping experiments. These compounds readily undergo reaction with tetra-nbutylammonium cyanide. The cyanide reaction is 10-100× faster when the solution is irradiated with 350 nm light. Reaction with trimethylsilyl cyanide occurs only with UV irradiation demonstrating photoreactivity. The rate of tetrahydrochromeno[2,3-b]indole ring-opening is greater for (i) Me substitution at the hemiaminal carbon (compared to Ph), and (ii) substitution of fluorine at the 9-position of the indole. Under acidic conditions, the ring-opened indolium ion is observed.
A conformational analysis of o-fluoro Z-azobenzene reveals a slight preference for aromatic C-F/π interaction. Density functional theory (DFT) indicates that the conformation with a C-F/π interaction is preferred by approximately 0.3-0.5 kcal/mol. Ground-state conformations were corroborated with X-ray crystallography. (Z)-Azobenzene (Z-AB) with at least one o-fluoro per ring displays (19)F-(19)F through-space (TS) coupling. 2D J-resolved NMR was used to distinguish through-bond from TS coupling ((TS)JFF). (TS)JFF decreases as the temperature is lowered and the multiplets coalesce into broad singlets. We hypothesize that the coalescence temperature (Tc) corresponds to the barrier for phenyl rotation. The experimentally determined barrier of 8-10 kcal/mol has been qualitatively verified by DFT where transition states with a bisected geometry were identified with zero-point energies of 6-9 kcal/mol relative to ground state. These values are significantly higher that values estimated from previous theoretical studies but lie within a reasonable range for phenyl rotation in hydrocarbon systems.
Based on the Gardner, et al. (1959) interpretation of the leveling-sharpening dimension, order of presentation and length of viewing time were manipulated on a size-estimation task. Contrary to expectation, neither variable significantly affected performance, and four different subject-estimation patterns were isolated rather than the two patterns (leveling and sharpening) expected. Both magnitude and directional properties of the four estimation patterns were explained by a modified version of Parducci's range-frequency model.
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