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Understanding the Fundamental Role of π/π, σ/σ, and σ/π Dispersion Interactions in Shaping Carbon‐Based Materials 下载免费PDF全文
Dr. Mercedes Alonso Tatiana Woller Dr. Francisco J. Martín‐Martínez Dr. Julia Contreras‐García Prof. Paul Geerlings Prof. Frank De Proft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4931-4941
Noncovalent interactions involving aromatic rings, such as π‐stacking and CH/π interactions, are central to many areas of modern chemistry. However, recent studies proved that aromaticity is not required for stacking interactions, since similar interaction energies were computed for several aromatic and aliphatic dimers. Herein, the nature and origin of π/π, σ/σ, and σ/π dispersion interactions has been investigated by using dispersion‐corrected density functional theory, energy decomposition analysis, and the recently developed noncovalent interaction (NCI) method. Our analysis shows that π/π and σ/σ stacking interactions are equally important for the benzene and cyclohexane dimers, explaining why both compounds have similar boiling points. Also, similar dispersion forces are found in the benzene???methane and cyclohexane???methane complexes. However, for systems larger than naphthalene, there are enhanced stacking interactions in the aromatic dimers adopting a parallel‐displaced configuration compared to the analogous saturated systems. Although dispersion plays a decisive role in stabilizing all the complexes, the origin of the π/π, σ/σ, and σ/π interactions is different. The NCI method reveals that the dispersion interactions between the hydrogen atoms are responsible for the surprisingly strong aliphatic interactions. Moreover, whereas σ/σ and σ/π interactions are local, the π/π stacking are inherently delocalized, which give rise to a non‐additive effect. These new types of dispersion interactions between saturated groups can be exploited in the rational design of novel carbon materials. 相似文献
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C. David Sherrill Bobby G. Sumpter Mutasem O. Sinnokrot Michael S. Marshall Edward G. Hohenstein Ross C. Walker Ian R. Gould 《Journal of computational chemistry》2009,30(14):2187-2193
Several popular force fields, namely, CHARMM, AMBER, OPLS‐AA, and MM3, have been tested for their ability to reproduce highly accurate quantum mechanical potential energy curves for noncovalent interactions in the benzene dimer, the benzene‐CH4 complex, and the benzene‐H2S complex. All of the force fields are semi‐quantitatively correct, but none of them is consistently reliable quantitatively. Re‐optimization of Lennard‐Jones parameters and symmetry‐adapted perturbation theory analysis for the benzene dimer suggests that better agreement cannot be expected unless more flexible functional forms (particularly for the electrostatic contributions) are employed for the empirical force fields. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
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The cis-oxa- ( 13a-d ) and -aza-σ-bishomobenzene ( 13 e ) derivatives have been synthesized; they are sufficiently stable to be isolated in pure form. On heating, 13a-e are easily isomerized into the π-bishomobenzene analogues 14a-e , the processes 13 a ? 14 a , 13 b ? 14b and 13d ? 14d being reversible. Some kinetic and thermodynamic data for these σ, π,bishomobenzene transformations are presented. 相似文献
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Laser flash photolyses (λ = 265mm) of the γ,λ-epoxyenones 1–3, 7 and 8 , the α,β-unsaturated γ,δ-epoxy ester 6 , and the epoxytriene 9 at ambient temperature produced short-lived transients with broad absorption maxima in the visible region, which are identified as carbonyl ylides. Comparison of the rather long-wavelength absorption maxima with the results of standard PPP SCF SCI calculations suggests that some degree of twisting is present in all the ylides studied. The lifetimes of the order of hundreds of ns of these intermediates and Stern-Volmer analysis of the trapping of the carbonyl ylide derived from 2 with CH3COOH provide conclusive evidence that the carbene products are not formed via the carbonyl-ylide intermediate (Scheme 3). 相似文献
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The two components of the dual phosphorescence of 1-indanone ( 1 ) and six related ketones ( 2–7 ) possess different excitation spectra exhibiting the vibrational progression characteristic of the S0 → S1 (n, π*) transition (shorter-lived emission) and two bands of the S0 → S2 and 3 (π,π*) 0–0 transitions, respectively. The most favorable intersystem crossing routes are S1 (n, π*) → T (n, π*) and S2,3 (π*) → T (π, π*). Internal conversion to S1 competes more effectively with S (π, π*) → T (π, π*) intersystem crossing only from higher vibrational levels of the S2 and S3 states. 相似文献
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Redox‐Switchable 20π‐, 19π‐, and 18π‐Electron 5,10,15,20‐Tetraaryl‐5,15‐diazaporphyrinoid Nickel(II) Complexes 下载免费PDF全文
Takaharu Satoh Prof. Dr. Mao Minoura Prof. Dr. Haruyuki Nakano Prof. Dr. Ko Furukawa Prof. Dr. Yoshihiro Matano 《Angewandte Chemie (International ed. in English)》2016,55(6):2235-2238
The first examples of air‐stable 20π‐electron 5,10,15,20‐tetraaryl‐5,15‐diaza‐5,15‐dihydroporphyrins, their 18π‐electron dications, and the 19π‐electron radical cation were prepared through metal‐templated annulation of nickel(II) bis(5‐arylamino‐3‐chloro‐8‐mesityldipyrrin) complexes followed by oxidation. The neutral 20π‐electron derivatives are antiaromatic and the cationic 18π‐electron derivatives are aromatic in terms of the magnetic criterion of aromaticity. The meso N atoms in these diazaporphyrinoids give rise to characteristic redox and optical properties for the compounds that are not typical of isoelectronic 5,10,15,20‐tetraarylporphyrins. 相似文献
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Cover Picture: Understanding the Fundamental Role of π/π, σ/σ, and σ/π Dispersion Interactions in Shaping Carbon‐Based Materials (Chem. Eur. J. 17/2014) 下载免费PDF全文
Dr. Mercedes Alonso Tatiana Woller Dr. Francisco J. Martín‐Martínez Dr. Julia Contreras‐García Prof. Paul Geerlings Prof. Frank De Proft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(17):4841-4841
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Janusz Zakrzewski Charles Giannotti 《Journal of photochemistry and photobiology. A, Chemistry》1991,60(3):289-294
A laser flash photolysis study of a binuclear methyl (η1-azaferrocene)cobaloxime is reported. Excitation at 355 nm (4 ns, approximately 60 mJ) results in the reversible electron transfer between cobalt and iron centres COIII/FeII COII/FeIII. This constitutes the first example of photoinduced metal-to-metal electron transfer across a heterocyclic σ, π-bridge 相似文献
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It has been proved by NMR. measurements at low temperatures that the ligand displacement reactions of (π-all)Pd(π-C5H5) and Lewis bases L yielding PdL4 proceed by a π → σ rearrangement of the allylic group as the primary step. The organic reaction product is the 1-isomer of the corresponding allylcyclopentadiene but in the reactions of (π-1,1,2-Me3C3H2)Pd(π-C5H5) with L besides the isomeric allylcyclopentadienes also 2,3-dimethylbutadiene and cyclopentadiene are formed. The reaction mechanism will be discussed. 相似文献
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