Diarylhalonium compounds provide new opportunities as reagents and catalysts in the field of organic synthesis. The three center, four electron (3c–4e) bond is a center piece of their reactivity, but structural variation among the diarylhaloniums, and in comparison with other λ 3 -iodanes, indicates that the model needs refinement for broader applicability. We use a combination of Density Functional Theory (DFT), Natural Bond Orbital (NBO) Theory, and X-ray structure data to correlate bonding and structure for a λ 3 -iodane and a series of diarylchloronium, bromonium, and iodonium salts, and their isoelectronic diarylchalcogen counterparts. This analysis reveals that the s-orbital on the central halogen atom plays a greater role in the 3c–4e bond than previously considered. Finally, we show that our revised bonding model and associated structures account for both kinetic and thermodynamic reactivity for both acyclic phenyl(mesityl)halonium and cyclic dibenzohalolium salts.
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To Be or Not to Be: Demystifying the 2nd‐Quantized Picture of Complex Electronic Configuration Patterns in Chemistry with Natural Poly‐Electron Population Analysis
We provide a didactic introduction to 2nd‐quantized representation of complex electron–hole (
- NSF-PAR ID:
- 10461123
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Computational Chemistry
- Volume:
- 40
- Issue:
- 15
- ISSN:
- 0192-8651
- Page Range / eLocation ID:
- p. 1509-1520
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Local correlation methods rely on the assumption that electron correlation is nearsighted. In this work, we develop a method to alleviate this assumption. This new method is demonstrated by calculating the random phase approximation (RPA) correlation energies in several one‐dimensional model systems. In this new method, the first step is to approximately decompose the RPA correlation energy to the nearsighted and farsighted components based on the wavelength decomposition of electron correlation developed by Langreth and Perdew. The short‐wavelength (SW) component of the RPA correlation energy is then considered to be nearsighted, and the long‐wavelength (LW) component of the RPA correlation energy is considered to be farsighted. The SW RPA correlation energy is calculated using a recently developed local correlation method: the embedded cluster density approximation (ECDA). The LW RPA correlation energy is calculated globally based on the system's Kohn‐Sham orbitals. This new method is termed
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In this work hydrogen bonding in a diverse set of 36 unnatural and the three natural Watson Crick base pairs adenine (A)–thymine (T), adenine (A)–uracil (U) and guanine (G)–cytosine (C) was assessed utilizing local vibrational force constants derived from the local mode analysis, originally introduced by Konkoli and Cremer as a unique bond strength measure based on vibrational spectroscopy. The local mode analysis was complemented by the topological analysis of the electronic density and the natural bond orbital analysis. The most interesting findings of our study are that (i) hydrogen bonding in Watson Crick base pairs is not exceptionally strong and (ii) the N–H⋯N is the most favorable hydrogen bond in both unnatural and natural base pairs while O–H⋯N/O bonds are the less favorable in unnatural base pairs and not found at all in natural base pairs. In addition, the important role of non-classical C–H⋯N/O bonds for the stabilization of base pairs was revealed, especially the role of C–H⋯O bonds in Watson Crick base pairs. Hydrogen bonding in Watson Crick base pairs modeled in the DNA via a QM/MM approach showed that the DNA environment increases the strength of the central N–H⋯N bond and the C–H⋯O bonds, and at the same time decreases the strength of the N–H⋯O bond. However, the general trends observed in the gas phase calculations remain unchanged. The new methodology presented and tested in this work provides the bioengineering community with an efficient design tool to assess and predict the type and strength of hydrogen bonding in artificial base pairs.more » « less
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Abstract What happens when a C−H bond is forced to interact with unpaired pairs of electrons at a positively charged metal? Such interactions can be considered as “contra‐electrostatic” H‐bonds, which combine the familiar orbital interaction pattern characteristic for the covalent contribution to the conventional H‐bonding with an unusual contra‐electrostatic component. While electrostatics is strongly stabilizing component in the conventional C−H⋅⋅⋅X bonds where X is an electronegative main group element, it is destabilizing in the C−H⋅⋅⋅M contacts when M is Au(I), Ag(I), or Cu(I) of NHC−M−Cl systems. Such remarkable C−H⋅⋅⋅M interaction became experimentally accessible within (α‐ICyDMe)MCl, NHC‐Metal complexes embedded into cyclodextrins. Computational analysis of the model systems suggests that the overall interaction energies are relatively insensitive to moderate variations in the directionality of interaction between a C−H bond and the metal center, indicating stereoelectronic promiscuity of fully filled set of
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