Conformational behavior, interconversion conformers

The above energy profiles suggest significantly different conformational behavior in 7-10 both in terms of preferred geometries and modes of conformational interconversion in the gas phase. Inherent in the above analysis is the assumption that the 3-21G calculations provide a reliable picture of gas phase behavior. Of course, this assumption will require validation through calculations with more sophisticated basis sets, especially those employing d-orbitals (e.g., 6-31G ). 

In addition, all representatives are highly fluorescent in the solid state, but essentially nonfluorescent in solution at room temperature. Upon cooling the solutions of benzo[b][l,4]diazepines 51 cryo-fluorescence is observed, which can be attributed to a freezing of the ring interconversion and aggregation. This thermo responsive behavior of fluorophores as a consequence of restricted conformational... 

The conformational landscapes of two ILs build from [NTf2] and from /V-propyl-and /V-butyI -A -methylpyrroIidinium were investigated from Raman spectroscopy, MD, and ab initio techniques [135], For [NTf2] the three-dimensional PES and the corresponding MD simulations confirmed the existence of two stable isomers (see also [37, 36]). The anion was calculated to be flexible, albeit hindered, but capable of interconversion between conformers in the liquid state, a result also confirmed by the Raman data. In the case of the ALV-dialkylpyrrolidinium cations, the PES showed a much more limited conformational behavior of the pyrrolidinium ring [135],... 

Crystallographic evidence amply demonstrates that the trioxane ring is similar in shape and conformational preference to cyclohexane. The barrier for chair-to-chair interconversion, a hitherto unknown quantity, has been determined by a dynamic NMR spectral study <93JCS(P1)1927). The behavior of 3,3,5,5,6,6-hexamethyl-1,2,4-trioxane (27) is typical. Despite the high degree of substitution, MM3 calculations show that it exists as a chair in the ground state. The value determined... 

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