ELECTRONIC-STRUCTURE OF METHYLACETYLENE RADICAL-ANION - AN EPR AND MOSTUDY

An EPR and MO study has been carried out to elucidate the electronic s tructure of methylacetylene (MA) radical anion generated in glassy 2- methyltetrahydrofuran matrix by ionization radiation at 77 K. The EPR spectrum was dominated by a large and slightly anisotropic H-1 hf spli tting of ca. 4.53 mT due to one ethynyl proton. With the help of a sel ectively deuteriated methylacetylene, MA-d(3), the anisotropic hf and g-values were determined: the principal hf ((A) over tilde) and (g) ov er tilde values are A(xx) = 5.36 mT, A(yy) = 4.39 mT, A(zz) = 3.85 mT for, the ethynyl proton, a = 0.50 mT for the methyl protons, and g(xx) = 2.0005, g(yy) = 2.0020, g(zz) = 2.0021, respectively. From a compar ison of the experimental values with the theoretical ones calculated b y ab initio MO and INDO methods, a trans-bent structure was concluded for MA(-). The formation of MA(-) was also confirmed by an electron ab sorption spectroscopic study.