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351.
The conformational behavior of 1,2-difluoroethane (1), 1,2-dichloroethane (2), 1,2-dibromoethane (3), and 1,2-diiodoethane (4) have been analyzed by means of complete basis set CBS-QB3, hybrid-density functional theory (B3LYP/Def2-TZVPP) based methods
and natural bond orbital (NBO) interpretation. Both methods showed the expected greater stability of the gauche conformation
of compound 1 compared to its anti conformation. Contrary to compound 1, the anti conformations of compounds 2–4 are more stable than their gauche conformation. The stability of the anti conformation compared to the gauche conformation
increases from compound 1 to compound 4. The NBO analysis of donor–acceptor (σ → σ*) interactions showed that the generalized anomeric effect (GAE) is in favor of
the gauche conformation of compound 1. Contrary to compound 1, GAE is in favor of the anti conformations of compounds 2–4. The GAE values calculated (i.e., GAEanti − GAEgauche) increase from compound 1 to compound 4. On the other hand, the calculated dipole moment values for the gauche conformations decrease from compound 1 to compound 4. In the conflict between the GAE and dipole moments, the former succeeded in accounting for the increase of the anti conformation
stability from compound 1 to compound 4. There is a direct correlation between the calculated GAE, ∆[r
c–c(G) − r
c–c(A)] and ∆[r
c–x(A) − r
c–x(G)] parameters. The correlations between the GAE, bond orders, total steric exchange energies (TSEEs), ΔG
Anti–Gauche, ΔG
‡(Gauche → Gauche′, C
2v), ΔG
‡(Anti → Gauche, C
2), dipole–dipole interactions, structural parameters, and conformational behaviors of compounds 1–4 have been investigated. 相似文献
352.
Dr. Davood Zare Prof. Dr. Claude Piguet Dr. Alessandro Prescimone Prof. Dr. Catherine E. Housecroft Prof. Dr. Edwin C. Constable 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(42):e202200912
The allosteric positive cooperativity accompanying the formation of compact [CuI(α,α′-diimine)2]+ building blocks contributed to the historically efficient synthesis of metal-containing catenates and knotted assemblies. However, its limited magnitude can easily be overcome by the negative chelate cooperativity that controls the overall formation of related polymetallic multistranded helicates and grids. Despite the more abundant use of analogous dioxygen-resistant [AgI(α,α′-diimine)2]+ units in modern entangled metallo-supramolecular assemblies, a related thermodynamic justification was absent. Solid-state structural characterizations show the successive formation of [AgI(α,α′-diimine)(CH3CN)][X] and [AgI(α,α′-diimine)2][X] upon the stepwise reactions of α,α′-diimine=2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) derivatives with AgX (X=BF4−, ClO4−, PF6−). In room-temperature, 5–10 mM acetonitrile solutions, these cationic complexes exist as mixtures in fast exchange on the NMR timescale. Spectrophotometric titrations using the unsubstituted bpy and phen ligands point to the statistical (=non-cooperative) binding of two successive bidentate ligands around AgI, a mechanism probably driven by the formation of hydrophobic belts, that overcomes the unfavorable decrease in the positive charge borne by the metallic cation. Surprisingly, the addition of methyl groups adjacent to the nitrogen donors (6,6′ positions in dmbpy; 2,9 positions in dmphen) induces positive cooperativity for the formation of [Ag(dmbpy)2]+ and [Ag(dmphen)2]+, a trend assigned to additional stabilizing interligand interactions. Adding rigid and polarizable phenyl side arms in [Ag(Brdmbpy)2]+ further reinforces the positively cooperative process, while limiting the overall decrease in metal–ligand affinity. 相似文献
353.
Davood Azarifar Kaveh Khosravi Zohreh Najminejad Khadijeh Soleimani 《Journal of the Iranian Chemical Society》2012,9(3):321-326
Selective and efficient bromination and iodination of aromatic compounds by ammonium bromide and ammonium iodide, respectively, under promotion of trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane have been explored. Mild reaction conditions, high selectivity and yield, and high reaction rate are some of the major advantages of this synthetic method. 相似文献
354.
Mohammad Ali Zolfigol Iraj Mohammadpoor-Baltork Davood Habibi BiBi Fatemeh Mirjalili Abdolhamid Bamoniri 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2189-2193
Trimethylsilyl ethers were converted to their corresponding alcohols in the presence Nafion-H® and wet SiO 2 with good-to-excellent yields under mild and heterogeneous conditions. 相似文献
355.
356.
Behrooz Maleki Davood Azarifar Seyede Fateme Hojati Hojat Veisi Mostafa Gholizadeh Hafezeh Salehabadi Mona Khodaverdian Moghadam 《Journal of heterocyclic chemistry》2011,48(2):449-453
2,4,6‐Trichloro‐1,3,5‐triazine efficiently catalyzed the condensation reactions between 2‐aminothiophenol and aromatic aldehydes to afford 2‐arylbenzothiazolles in good‐to‐excellent yields. Simple and mild reaction conditions, the use of a cheap catalyst and easy work up, and isolation are notable features of this method. J. Heterocyclic Chem., (2011). 相似文献
357.