Irradiation of 1-naphthonitrile in the presence of 1,2-dimethylcyclopentene results in the formation of 2 + 2 cycloadducts with both the nitrile group and aromatic ring. Both types of addition occur via singlet 1-naphthonitrile. The ratio of nitrile/ring addition in ethyl ether solution is dependent upon dimethylcyclopentene concentration, oxygen concentration, and excitation wavelength. These results require kinetically nonequivalent singlet-state precursors for nitrile vs. ring addition. With the aid of a recent fluorescence polarization study by Suzuki, we assign ring adduct formation to the 1La state and nitrile adduct formation to either the 1Lb state or a hidden state with bent nitrile geometry. This assignment provides the first example of divergent reaction pathways for two nearly isoenergetic singlet states. The chemical behavior of the 1Lb, vs. 1La states is discussed in terms of the electronic description of these states provided by a molecular orbital (INDO/S) calculation. The results and conclusions of the present investigation are shown to be compatible with the extensive photophysical investigations of the 1-naphthonitrile/1,2-dimethylcyclopentene system by Ware and co-workers.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry