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904.
Assessment of the aromaticity of borepin rings by spectroscopic,crystallographic and computational methods: a historical overview
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This review presents a chronological discussion of the evolution of our conceptual and experimental understanding of aromaticity as pertaining to the borepin ring structure. Borepin is the boron‐containing charge‐neutral analogue of the carbocyclic tropylium ion, and many molecular variations involving the borepin motif have been synthesized over the past half century. The aromaticity of the borepin system has been probed with ultraviolet–visible (UV–vis), photoluminescence and infrared (IR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, X‐ray crystallography and computational analysis. Recently, the focus of borepin‐containing compounds has shifted to π‐electron materials, building on the foundation of a firm understanding of the physical organic properties of the borepin motif that will allow for electronic fine‐tuning toward desired applications. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
905.
Dr. Jun Zhu Dr. Heather A. Fogarty Dr. Helene Möllerstedt Dr. Maria Brink Dr. Henrik Ottosson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10698-10707
A density functional theory study on olefins with five‐membered monocyclic 4n and 4n+2 π‐electron substituents (C4H3X; X=CH+, SiH+, BH, AlH, CH2, SiH2, O, S, NH, and CH?) was performed to assess the connection between the degree of substituent (anti)aromaticity and the profile of the lowest triplet‐state (T1) potential‐energy surface (PES) for twisting about olefinic C?C bonds. It exploited both Hückel’s rule on aromaticity in the closed‐shell singlet ground state (S0) and Baird’s rule on aromaticity in the lowest ππ* excited triplet state. The compounds CH2?CH(C4H3X) were categorized as set A and set B olefins depending on which carbon atom (C2 or C3) of the C4H3X ring is bonded to the olefin. The degree of substituent (anti)aromaticity goes from strongly S0‐antiaromatic/T1‐aromatic (C5H4+) to strongly S0‐aromatic/T1‐ antiaromatic (C5H4?). Our hypothesis is that the shapes of the T1 PESs, as given by the energy differences between planar and perpendicularly twisted olefin structures in T1 [ΔE(T1)], smoothly follow the changes in substituent (anti)aromaticity. Indeed, correlations between ΔE(T1) and the (anti)aromaticity changes of the C4H3X groups, as measured by the zz‐tensor component of the nucleus‐independent chemical shift ΔNICS(T1;1)zz, are found both for sets A and B separately (linear fits; r2=0.949 and 0.851, respectively) and for the two sets combined (linear fit; r2=0.851). For sets A and B combined, strong correlations are also found between ΔE(T1) and the degree of S0 (anti)aromaticity as determined by NICS(S0,1)zz (sigmoidal fit; r2=0.963), as well as between the T1 energies of the planar olefins and NICS(S0,1)zz (linear fit; r2=0.939). Thus, careful tuning of substituent (anti)aromaticity allows for design of small olefins with T1 PESs suitable for adiabatic Z/E photoisomerization. 相似文献
906.
Subrata Mahanta Bijan Kumar Paul Rupashree Balia Singh Nikhil Guchhait 《Journal of computational chemistry》2011,32(1):1-14
The inequivalence of substitution pair positions of naphthalene ring has been investigated by a theoretical measurement of hydrogen bond strength, aromaticity, and excited state intramolecular proton transfer (ESIPT) reaction as the tools in three substituted naphthalene compounds viz 1‐hydroxy‐2‐naphthaldehyde (HN12), 2‐hydroxy‐1‐naphthaldehyde (HN21), and 2‐hydroxy‐3‐naphthaldehyde (HN23). The difference in intramolecular hydrogen bond (IMHB) strength clearly reflects the inequivalence of substitution pairs where the calculated IMHB strength is found to be greater for HN12 and HN21 than HN23. The H‐bonding interactions have been explored by calculation of electron density ρ(r) and Laplacian ?2ρ(r) at the bond critical point using atoms in molecule method and by calculation of interaction between σ* of OH with lone pair of carbonyl oxygen atom using NBO analysis. The ground and excited state potential energy surfaces (PESs) for the proton transfer reaction at HF (6‐31G**) and DFT (B3LYP/6‐31G**) levels are similar for HN12, HN21 and different for HN23. The computed aromaticity of the two rings of naphthalene moiety at B3LYP/6‐31G** method also predicts similarity between HN12 and HN21, but different for HN23. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010 相似文献
907.
Wouter Heyndrickx Pedro Salvador Patrick Bultinck Miquel Solà Eduard Matito 《Journal of computational chemistry》2011,32(3):386-395
Several definitions of an atom in a molecule (AIM) in three‐dimensional (3D) space, including both fuzzy and disjoint domains, are used to calculate electron sharing indices (ESI) and related electronic aromaticity measures, namely, Iring and multicenter indices (MCI), for a wide set of cyclic planar aromatic and nonaromatic molecules of different ring size. The results obtained using the recent iterative Hirshfeld scheme are compared with those derived from the classical Hirshfeld method and from Bader's quantum theory of atoms in molecules. For bonded atoms, all methods yield ESI values in very good agreement, especially for C–C interactions. In the case of nonbonded interactions, there are relevant deviations, particularly between fuzzy and QTAIM schemes. These discrepancies directly translate into significant differences in the values and the trends of the aromaticity indices. In particular, the chemically expected trends are more consistently found when using disjoint domains. Careful examination of the underlying effects reveals the different reasons why the aromaticity indices investigated give the expected results for binary divisions of 3D space. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011. 相似文献
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909.
Tanaka T Lee BS Aratani N Yoon MC Kim D Osuka A 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(51):14400-14412
Hybrid porphyrin tapes 3 and 4 , consisting of a mixture of 3,5‐di‐tert‐butylphenyl‐substituted donor‐type ZnII–porphyrins and pentafluorophenyl‐substituted acceptor‐type ZnII–porphyrins, were prepared by a synthetic route involving cross‐condensation reaction of a NiII–porphyrinyldipyrromethane and pentafluorophenyldipyrromethane with pentafluorobenzaldehyde followed by appropriate demetalation, remetalation, and oxidative ring‐closure reaction. The NiII‐substituted porphyrin tapes 5 (Ni‐Zn‐Ni) and 6 (Ni‐H2‐Ni) were also prepared through similar routes. The hybrid porphyrin tapes 3 and 4 are more soluble and more stable than normal porphyrin tapes 1 and 2 consisting of only donor‐type ZnII–porphyrins. The solid‐state and crystal packing structures of 3 , 4 , and 5 were elucidated by single‐crystal X‐ray diffraction analysis. Singly meso–meso‐linked hybrid porphyrin arrays 12 and 14 exhibit redox potentials that roughly correspond to each constituent porphyrin segments, while the redox potentials of the hybrid porphyrin tapes 3 and 4 are positively shifted as a whole. The two‐photon absorption (TPA) values of 1–6 were measured by using a wavelength‐scanning open aperture Z‐scan method and found to be 1900, 21 000, 2200, 27 000, 24 000, and 26 000 GM, respectively. These results illustrate an important effect of elongation of π‐electron conjugation for the enhancement of TPA values. The hybrid porphyrin tapes show slightly larger TPA values than the parent ones. 相似文献
910.
Mohammed F. Arshad Aftab Alam Abdullah Ayed Alshammari Mohammed Bader Alhazza Ibrahim Mohammed Alzimam Md Anish Alam Gulam Mustafa Md Salahuddin Ansari Abdulelah M. Alotaibi Abdullah A. Alotaibi Suresh Kumar Syed Mohammed Basheeruddin Asdaq Mohd. Imran Pran Kishore Deb Katharigatta N. Venugopala Shahamah Jomah 《Molecules (Basel, Switzerland)》2022,27(13)