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

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 He I photoelectron spectra of peri-amino and dimethylamino naphthalenes are presented. The differences in the ionization energies of the π-bands are interpreted by separation of the perturbation of the amino substituent into an inductive destabilization and conjugative stabilization. This affords the assignment of the photoelectron bands of ionization energies below 11 eV and an estimation of the dihedral angle in the peri-dimethylamino derivatives. The data on the peri-amino naphthalenes indicate some angular distortion in contrast to 2-aminonaphthalene.

Photoelectron Spectroscopy of peri‐Amino Naphthalenes

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.

Zuzana Lanyjova

Papers

Quadricyclanes. Part I: Photoelectron spectra and electronic structure

Quadricyclanes part 1, photoelectron spectra and electronic structure