The results of studies on intramolecular interconversions in systems of norbornadiene quadricyclane and their derivatives are classified and discussed. The mechanisms of the forward photoreaction and reverse thermal process in relation to the nature of the substituents and carbocycles, type of sensitiser and catalyst, and properties of the medium are discussed in detail and classified. An analysis is made of the influence of these factors on the spectroscopic, kinetic, and thermodynamic properties of this system as an accumulator and converter of light energy. Methods of improving its characteristics — light absorption, the quantum yield of the photoreaction, and stability of the photoproduct — have been established. The bibliography includes 188 references.

https://iopscience.iop.org/article/10.1070/RC1991v060n05ABEH001088/pdf

Norbornadiene-quadricyclane — an effective molecular system for the storage of solar energy

Classical structural formulas often convey the impression only those relationships between the atoms are of importance which hold a molecule together as symbolized by the chemical bonds. However, many interactions between atoms or groups of atoms are not adequately denoted in this manner. Nevertheless, their existence can have important consequences for ground state energies (cis-difluoroethylene is more stable than trans-difluoroethylene), conformations (the syn form of methyl vinyl ether is more stable than the anti form), reactivities (an endo cyclopropane ring in 7-anti-norbornyl derivatives accelerates solvolysis by a factor of 1014), UV spectra (“superposition” of the π-systems of acridine and purine-bonded through a four-membered chain-results in hypochromism), CD spectra (the inherently symmetrical but dissymmetrically perturbed chromophore of 2-deuterionorbornadiene allows the observation of three transitions in the near UV), and ESR spectra (the long-range coupling with H-4 in the bridgehead bicyclo[2.1.1]hex-1-yl radical equals 22.5 G). Since orbital interactions are involved in most intramolecular effects of this kind, photoelectron spectroscopy has proven an informative and valuable extension to other methods.

Proximity Effects in Organic Chemistry—The Photoelectron Spectroscopic Investigation of Non‐Bonding and Transannular Interactions

Photoelectron spectra and bonding in small ring hydrocarbons

Photoelectron spectroscopy (PES) provides valuable information on the ionization energies of atoms and molecules. The ionization energy (IE) is given by the relation. hv = IE + T where hv is t h e energy of the radiation and T i s the kinetic energy of the electron. The IEs are directly related to the orbital energies (Koopmans' theorem). By employing UV radiation (HeI. 21.2 eV. or HeII. 40.8 eV). extensive data on the ionization of valence electrons in organic molecules have been obtained in recent years. These studies of UV photoelectron spectroscopy. originated by Turner, have provided a direct probe into the energy levels of organic molecules. Molecular orbital calculations of various degrees of sophistication are generally employed to make assignments of the PES bands. Analysis of the vibrational structure of PES bands has not only provided structural information on the molecular ions, but has also been of value in band assignments. Dewar and co-workers [1, 2) presented summaries of availabl...

Systematic Organic UV Photoelectron Spectroscopy

Klassische Strukturformeln vermitteln haufig die Vorstellung, einzig und allein jene Beziehungen zwischen den Atomen seien von Bedeutung, welche fur den Zusammenhalt des Molekuls sorgen und durch Bindungsstriche wiedergegeben werden. Viele Wechselwirkungen zwischen Atomen oder Atomgruppen werden jedoch durch diese Schreibweise nicht erfast. Ihre Anwesenheit hat dennoch mitunter wichtige Konsequenzen fur Grundzustandsenergien (cis-Difluorethylen ist stabiler als trans-Difluorethylen), Konformationen (syn-Methylvinylether ist stabiler als die anti-Form), Reaktivitaten (ein endo-standiger Cyclopropanring in 7-anti-Norbornylderivaten beschleunigt die Solvolyse um den Faktor 1014), UV-Spektren (die π-Systeme von Acridin und Purin – durch eine viergliedrige Kette verbunden — ergeben beim “Ubereinanderlegen” Hypochromie), CD-Spektren (der inharent symmetrische, dissymmetrisch gestorte Chromophor von 2-Deuterionorbornadien last drei Ubergange im nahen UV erkennen) und ESR-Spektren (die Fernkopplung mit H-4 im Bruckenkopf-Radikal Bicyclo[2.1.1]hex-1-yl betragt 22.5 G). An den meisten intramolekularen Effekten dieser Art sind Orbitalwechselwirkungen beteiligt; die Photoelektronenspektroskopie hat sich wie erwartet als aussagekraftige und wertvolle Erganzung der anderen Methoden erwiesen.

Proximitätseffekte in der Organischen Chemie — Die photoelektronenspektroskopische Untersuchung nichtbindender und transanularer Wechselwirkungen

The photoelectron spectra of quadricyclane (3) and 3-methylidene quadricyclane (4) have been measured. The results served as a basis for the elucidation of the electronic structure of these compounds, which agreed with theoretical calculations. It is found that the symmetry of the HOMO of 3 is different when compared to that of its valence isomer norbornadiene (1). The results also indicate that the structure of the highest occupied orbitals cannot be derived by only considering the Walsh-orbitals of the two three-membered rings. In addition one of the Walsh-components of the four-memebered ring has to be taken into account.

Quadricyclanes. Part I: Photoelectron spectra and electronic structure

Um die Orbitalsequenz im Bishomofulven 3 und im „Snouten” 4 zu erhalten, wurden ihre Photoelektronenspektren zusammen mit denen der homologen Quadricyclane 2, 5 und 6 interpretiert. In 3 herrscht eine starke Wechselwirkung Dreiring-Dreiring einerseits und Dreiring-Doppelbindung (β = −1.7eV) andererseits. Die Tatsache, das das erste Ionisationspotential von „Snouten” 4 Praktisch das gleiche ist wie das von Cyclopropabicyclo[2.2.2]octen 13, last sich auf zwei gegenlaufige Effekte zuruckfuhren. Die Sequenz von 2 wird mit der seiner beiden Nachbarn in der homologen Reihe, Triateran 14 und Quadricyclan 15, verglichen.



Bishomofulvene Conjugation. Photoelectron Spectra and Electronic Structure of Homologous Quadricyclanes



In order to obtain the orbital sequence in bishomofulvene 3 and „snouten” 4 their photoelectron spectra have been interpreted together with those of the homologous quadricyclanes 2, 5, and 6. In 3 a strong interaction prevails between the two cyclopropane moieties on the one side and the three-membered rings and the double bond on the other side. The fact that the first ionization potential of “snoutene” 4 equals that of cyclopropa-bicyclo[2.2.2]octene 13 may be explained by two opposite effects. The sequence in 2 is then compared to that of its neighbours in the homologous series, triasterane 14 and quadricyclane 15.

Bishomofulvenkonjugation. Photoelektronenspektren und Elektronenstruktur homologer Quadricyclane

Die stereochemie des diels-alder-adduktes von diphenylcyclopropen und cyclopentadien. Ein bemerkenswerter substituenteneffekt.

Anwendungen der photoelektronenspektroskopie 66. mitt. kleine ringe 13. mitt. bishomofulvenkonjugation, photoelektronenspektren und elektronenstruktur homologer quadricyclane

Constanze Heller

Papers

Quadricyclanes. Part I: Photoelectron spectra and electronic structure

Bishomofulvenkonjugation. Photoelektronenspektren und Elektronenstruktur homologer Quadricyclane

Die stereochemie des diels-alder-adduktes von diphenylcyclopropen und cyclopentadien. Ein bemerkenswerter substituenteneffekt.

Anwendungen der photoelektronenspektroskopie 66. mitt. kleine ringe 13. mitt. bishomofulvenkonjugation, photoelektronenspektren und elektronenstruktur homologer quadricyclane

Quadricyclanes part 1, photoelectron spectra and electronic structure