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The recently developed Gauge-Invariant (Including) Atomic Orbital (GIAO) based Time-Dependent Density Functional Theory (TDDFT) methodology for the calculation of transparent spectral region optical rotations of chiral molecules provides a new approach to the determination of absolute configurations. Here, we discuss the application of the TDDFT/GIAO methodology to chiral alkanes. We report B3LYP/aug-cc-pVDZ calculations of the specific rotations of the 22 chiral alkanes, 2-23, of well-established Absolute Configuration. The average absolute deviation of calculated and experimental [alpha](D) values for molecules 2-22 is 24.8. In two of the molecules 2-23, trans-pinane, 10, and endo-isocamphane, 13, the sign of [alpha](D) is incorrectly predicted. Our results demonstrate that absolute configurations of alkanes can be reliably assigned by using B3LYP/aug-cc-pVDZ TDDFT/GIAO calculations if, but only if, [alpha](D) is significantly greater than 25. In the case of (-)-anti-trans-anti-trans-anti-trans-perhydrotriphenylene, 1, [alpha](D) is -93 and TDDFT/GIAO calculations reliably lead to the absolute configuration R(-). 相似文献
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Cheeseman M Feuillet FJ Johnson AL Bull SD 《Chemical communications (Cambridge, England)》2005,(18):2372-2374
A new way of combining chiral auxiliaries and substrate-directable reactions for asymmetric synthesis is described that employs a three-step sequence of aldol-cyclopropanation-retro-aldol reactions for the stereoselective synthesis of enantiopure cyclopropane carboxaldehydes. 相似文献
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Pyrrolo[1,2-a[3,1]benzothiazepines were successfully synthesized from alkylthiopyrroles. The latter compounds were prepared from the appropriate N-aryl-2-thiocyanopyrroles. 2,3-Dihydro-3-oxo-4-phenylthieno[3,2-b]pyrrole ( 29 ) was obtained from acid treatment of the 2-pyrrolylthioacetic acid 28 . 相似文献
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Samuel Cheeseman Z. L. Shaw Jitraporn Vongsvivut Russell J. Crawford Madeleine F. Dupont Kylie J. Boyce Sheeana Gangadoo Saffron J. Bryant Gary Bryant Daniel Cozzolino James Chapman Aaron Elbourne Vi Khanh Truong 《Molecules (Basel, Switzerland)》2021,26(13)
Biofilms are assemblages of microbial cells, extracellular polymeric substances (EPS), and other components extracted from the environment in which they develop. Within biofilms, the spatial distribution of these components can vary. Here we present a fundamental characterization study to show differences between biofilms formed by Gram-positive methicillin-resistant Staphylococcus aureus (MRSA), Gram-negative Pseudomonas aeruginosa, and the yeast-type Candida albicans using synchrotron macro attenuated total reflectance-Fourier transform infrared (ATR-FTIR) microspectroscopy. We were able to characterise the pathogenic biofilms’ heterogeneous distribution, which is challenging to do using traditional techniques. Multivariate analyses revealed that the polysaccharides area (1200–950 cm−1) accounted for the most significant variance between biofilm samples, and other spectral regions corresponding to amides, lipids, and polysaccharides all contributed to sample variation. In general, this study will advance our understanding of microbial biofilms and serve as a model for future research on how to use synchrotron source ATR-FTIR microspectroscopy to analyse their variations and spatial arrangements. 相似文献
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The reactions which occur when 2-chloroquinoxaline is heated with an excess of aromatic amine are unexpectedly complex. For example, when 2-chloroquinoxaline is heated with excess aniline a mixture of the expected anilino derivative (1), 6H-indolo[2,3-b]quinoxaline (7), 2,3-dianilinoquinoxaline (11), and 2-p-ainino-phenyl-3-anilinoquinoxaline (16) is obtained. 相似文献
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Wilson SM Wiberg KB Cheeseman JR Frisch MJ Vaccaro PH 《The journal of physical chemistry. A》2005,109(51):11752-11764
Cavity ring-down polarimetry (CRDP) has been exploited to interrogate the nonresonant optical activity (or circular birefringence) of prototypical organic compounds in the vapor phase, thereby revealing the intrinsic chiro-optical response evoked from isolated (solvent-free) molecules. Specific polarization rotation parameters have been measured at two distinct excitation wavelengths (355 nm and 633 nm) for a variety of gas-phase species drawn from the terpene, epoxide, and alkane/alkene families, with complementary solution-phase polarimetric studies serving to highlight the pronounced influence of solute-solvent interactions. Time-dependent linear response calculations performed at high levels of density functional theory have been enlisted to unravel the structural and electronic origins for observed behavior. Aside from elucidating the complex solvation processes that mediate chiro-optical phenomena taking place in condensed media, this study affords a critical assessment for emerging ab initio predictions of nonresonant optical activity and for their promising ability to assist in the determination of absolute molecular stereochemistry. 相似文献
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The title compounds 15-18 and 26 are prepared by intramolecular cyclisation of the pyrrolylthiols derived from sodium borohydride reduction of N-aryl-thiocyanatopyrroles 11-14 and 25 . 相似文献
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J. K. Brooks Kazuyuki Saitô JD Maitland Wright 《Rendiconti del Circolo Matematico di Palermo》2003,52(1):5-14
LetA be aC*-algebra with second dualA″. Let (φ
n)(n=1,...) be a sequence in the dual ofA such that limφ
n(a) exists for eacha εA. In general, this does not imply that limφ
n(x) exists for eachx εA″. But if limφ
n(p) exists whenever p is the range projection of a positive self-adjoint element of the unit ball ofA, then it is shown that limφ
n(x) does exist for eachx inA″. This is a non-commutative generalisation of a celebrated theorem of Dieudonné. A new proof of Dieudonné’s theorem, for
positive measures, is given here. The proof of the main result makes use of Dieudonné’s original theorem. 相似文献