Determination of Ground State Spin Multiplicity of Basic non-Kekule Hydrocarbons by Measuring Paramagnetic Susceptibility.

2，3-二甲基环己-1，4-二基（1）是一个不相交的双自由基，其基态多重性仍有争议。用ESR波谱和磁性测量研究了标题化合物的基态多重性。以邻苯二甲酸为原料，按W. R. Roth的方法合成了5，6-二亚甲基-2，3-二氮杂双环[2，2，2]辛-2-烯。利用高压汞灯的光在MTHF基质中进行光解，得到1。光产物的大小与照射波长有关。312.6nm的光得到目标分子，302.2nm的光得到另一种产物。用直接测量磁化强度的方法研究了1的磁性。发现1的单重态和三重态几乎是简并的。这一结果是一个至关重要的决定的问题，有长期的争议之间的理论和实验。

2,3-Dimethylenecyclohexa-1,4-diyl (1) is a disjoint diradical and the ground-state multiplicity is still in controversy. By means of ESR spectroscopy and magnetic measurement, the ground-state multiplicity of the title compound was studied. From orthophtalic acid, 5,6-dimethylene-2,3-diazabicyclo[2,2,2, ]oct-2-ene was synthesized according to the method of W.R.Roth. The photolysis was carried out in MTHF matrix by using light from high-pressure mercury lamp to give 1. The photoproduct depended on the wavelenght of irradiation. The light of 312.6 nm gave the target molecule and the light of 302.2 nm gave another product. The magnetic property of 1 was investigated by means of direct measurement of the magnetization. It was found that the singlet and triplet state of 1 was almost degenerate. This result is a crucial determination of the problem where there has been a long controversy between theory and experiment.