Cyclopropyl Homoconjugation, Homoaromaticity and Homoantiaromaticity—Theoretical Aspects and Analysis

Cremer, Dieter; Childs, Ronald F.

doi:10.1002/9780470682531.pat0033

Cited by 4 publications

(10 citation statements)

References 168 publications

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“…On the other hand, increasing the distance between these carbons, as in 1-TS, makes these two orbitals much more C(2p )-like. The rather different shape of 7 in 1-TS, and its wider separation from the corresponding 1 , strongly suggest that the interaction between these two orbitals should be rather weak. An example intermediate between 1 and 1-TS can be seen in a SC study of bicyclic 1,6-methano [10]annulene ("homonaphthalene") 30 which describes an interaction between SC orbitals across a methylene bridge over a distance of 2.125Å.…”

Section: Resultsmentioning

confidence: 99%

“…1 As a consequence, we focus in this paper on the "no-bond" potentially homoaromatic systems 1, 2 and 3 and on the corresponding transition states 1-TS, 2-TS and 3-TS.…”

Section: Resultsmentioning

confidence: 99%

“…Homoconjugation and homoaromaticity (a detailed account of the history of these concepts can be found in refs − ) are usually interpreted using a simple orbital model: In a homoconjugated system, the continuous chain of p π orbitals contributed by sp 2 hybridized atoms is interrupted by one or more non-neighboring sp 3 hybridized atoms, but the p π orbital overlaps involving centers connected to an sp 3 hybridized atom remain sufficiently large so as to sustain conjugation; a homoaromatic molecule, following the well-known Hückel rule, includes a homoconjugated cycle with 4 n + 2 π electrons. A classical example of a Hückel-type homoaromatic molecule is provided by the homotropenylium ion, C 8 H 9 + (often referred to as homotropylium).…”

Section: Introductionmentioning

confidence: 99%

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Modern Valence-Bond Description of Homoaromaticity

Karadakov

2016

J. Phys. Chem. A

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Spin-coupled (SC) theory is used to obtain modern valence-bond (VB) descriptions of the electronic structures of local minimum and transition state geometries of three species that have been considered to exhibit homoconjugation and homoaromaticity: the homotropenylium ion, C 8 H C 9 , the cycloheptatriene neutral ring, C 7 H 8 , and the 1,3-bishomotropenylium ion, C 9 H C 11 . The resulting compact SC wavefunctions are of comparable quality to CASSCF constructions that are based on the same "N electrons in M orbitals" active spaces, but they are much easier to interpret directly. Analysis of the forms of the SC orbitals and of the overlaps between them, as well as an examination of the compositions of the associated resonance patterns, strongly suggest that both of the homotropenylium and 1,3-bishomotropenylium ions are homoaromatic at their local minimum geometries, with all of the other cases that were considered being non-aromatic. The SC results also show that the differences between "no-bond" and "bond" homoconjugated systems are very likely to be much smaller than previously thought.

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Section: Resultsmentioning

confidence: 99%

“…1 As a consequence, we focus in this paper on the "no-bond" potentially homoaromatic systems 1, 2 and 3 and on the corresponding transition states 1-TS, 2-TS and 3-TS.…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modern Valence-Bond Description of Homoaromaticity

Karadakov

2016

J. Phys. Chem. A

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“…Combined, these findings serve as important indication that homoannulene ester 15 and homoannulene carboxylic acid 16 are neutral homoaromatic compounds. One of the paramount characteristics for homoaromatic compounds is bond length equalization of the single and double bonds involved 1,2 . With the X-ray structures of 14, 15 and 16 available for detailed analysis, we observed significant shortening of the single bonds and elongation of the double bonds (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Homoaromatic molecules display characteristics of aromatic stabilization yet possess an interrupted cyclic conjugated -system 1 . The concept of homoaromaticity, resting upon through-bond or through-space homoconjugation 2,3 (the interaction between disconnected -systems, usually interrupted by one or more sp 3 -hybridized carbon atoms 1,4 ) has been highly controversial in the past 1 . The difficulty to identify clear criteria for the assignment of molecules as homoaromatic at first 1,5 as well as the small number of known homoaromatic molecules further spurred the discussion in this field.…”

Section: Introductionmentioning

confidence: 99%

Photoswitching neutral homoaromatic hydrocarbons

Ngoc

Grabicki²,

Irran

et al. 2022

Preprint

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The identification and characterization of homoaromatic compounds bearing an interrupted -system are fundamental challenges for the understanding of electronic interactions in organic molecules. This is further hampered by the fact that no stable neutral homoaromatic hydrocarbon is known. We present the preparation of a new class of neutral homoaromatic compounds, which are supported by experimental evidence (ring current observed by NMR spectroscopy, equalization of bond lengths through X-ray structure analysis) as well as computational analysis (NICS and ACID). Furthermore, we show that one homoaromatic hydrocarbon is a photoswitch through a reversible photochemical [1,11] sigmatropic rearrangement. We provide evidence that the local 6 homoaromatic state vanishes upon photoswitching to produce a purely global 10 homoaromatic state. These results of stable and accessible homoaromatic neutral hydrocarbons and their photoswitching behaviour provide new insights for the understanding and study of homoconjugative interactions in organic molecules, and for the design of new responsive molecular materials.

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Island Homoaromaticity in the W‐Shaped 2,4‐Diphospha‐3‐arsapentadienide Anion and Related Compounds – Theoretical and Experimental Investigations

et al. 2012

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A series of anions with general formula (R2C=P)2Pn– (Pn = N, P, As, Sb; R = H, Me, CF3, SiH3, SiMe3, SiF3) was investigated theoretically at the DFT (RI‐BP86/TZVP) and RI‐MP2/TZVP levels of approximation. Significantly sharpened central PPnP bond angles were predicted for the species with π‐acceptor R substituents. The corresponding bond angle values decrease in the order Pn = N >> P > As > Sb. This finding is in agreement with the previously published structural data for [(Me3Si)2C=P]2P–. An island homoaromaticity was proposed as a suitable explanation for the observed effect. In more detail, it consists of shifting negative charge to the electron‐withdrawing terminal groups with formation of a homologue of an aromatic heterocyclopropylium cation as the central moiety. Calculated structures and charge distributions are in agreement with the proposed model as well as with the molecular structure of the newly synthesized 2,4‐diphospha‐3‐arsapentadienyl anion.

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Cyclopropyl Homoconjugation, Homoaromaticity and Homoantiaromaticity—Theoretical Aspects and Analysis

Abstract: Introduction Definition of Homoconjugation and Homoaromaticity—Basic Considerations Theoretical Aspects of Defining, Detecting and Describing Homoconjugation and Homoaromaticity AB Initio Examinations of Homoconjugation Conclusions and Outlook Acknowledgeme… Show more

Cited by 4 publications

References 168 publications

Modern Valence-Bond Description of Homoaromaticity

Modern Valence-Bond Description of Homoaromaticity

Photoswitching neutral homoaromatic hydrocarbons

Island Homoaromaticity in the W‐Shaped 2,4‐Diphospha‐3‐arsapentadienide Anion and Related Compounds – Theoretical and Experimental Investigations

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