William C. Herndon

Luminescence spectra and photocycloaddition of the excited coumarins to DNA bases.

Abstract— The lowest excited singlet and triplet states of coumarin, psoralen, and 4‐hydroxy‐coumarin have been assigned to the (π,π*) type on the basis of the luminescence spectroscopy and MO calculations. The mechanism of photocycloaddition of courmarin and psoralen to thymine has been described in terms of the perturbational MO model and MO reactivity indices. All possible cycloaddition patterns have been examined. Results suggest that the 3,4‐bond of coumarin in the excited state is somewhat more reactive than the same bond of psoralen in the excited state. It is also predicted that the 3,4‐bond of psoralen in the triplet state is more reactive than the 4′, 5′‐bond. The results have been favorably correlated with the electronic characteristics of excited coumarin molecules and with available experimental data on the relative yields of photoadducts.

The gas phase retro-diels-alder reaction of bornylene. A question concerning pyrolytic reactions of bornyl and isobornyl halides and esters☆

(Receivad in USB 29 Hay 1968; received in UK for publication 20 November 1968) Bornylene (3,7,7-trimethylbicyclo[2.2.1]hept-2-ene) undergoes a retro-DielsAlder reaction at elevated temperatures in the gas phase to yield ethylene and 1,5,5-trimethylcyclopentadiene. The product 1,5,5-trimethylcyclopentadiene is unstable and a methyl shift occurs, giving rise to an equilibrium mixture of four C8 hydrocarbons (4).

Calorimetric Studies of Pi-Molecular Complexes

The work reported here is the result of an experimental calo-rimetric investigation of a series of intermolecular complexes which fall into the category labeled “charge transfer” complexes (1–5) or “donor-acceptor” complexes (4). Specifically, the systems studied consist of two compounds which are postulated to have an electron donor-acceptor relationship to one another (1). The donor molecules used were benzene, the methyl substituted benzenes, thianthrene, naphthalene, acenaphthalene, phenanthrene, and pyrene. The acceptor molecules were tetracyanoethylene (TCNE), 1,3,5-trinitrobenzene (TNB), and picric acid (1,3,5-trinitrophenol or PA). The calorimetric experiments were carried out in methylene chloride solution, all possible donor-acceptor combinations were used, and a 1:1 acceptor to donor complex constitution was assumed. These calorimetric investigations are the first studies of this type.