THE MICROWAVE-SPECTRA OF BENZOCYCLOBUTENE AND ITS DEUTERATED SPECIES

The microwave spectra of benzocyclobutene, benzocyclobutene-α-d1, and benzocyclobutene-α,α-d2, generated by pyrolysis of 3-isochromanone, 2-methylbenzyl chloride-α-d1, and 2-methylbenzyl chloride-α,α-d2, have been observed in the frequency range from 8.0 to 40.0 GHz. The rotational constants (MHz) have been determined as A = 4442.38(4), B = 2083.490(3), and C = 1444.563(3) for normal species, A = 4356.76(7), B = 2026.916(5), and C = 1414.307(8) for monodeuterated species, and A = 4277.91(8), B = 1972.942(7), and C = 1386.022(9) for dideuterated species in their ground vibrational states. The two excited vibrational states assigned in normal species are of the out-of-plane vibrational modes (va = 1 and vb = 1). The values of ΔI (= Ic - Ia - Ib) for normal, monodeuterated, and dideuterated species were found to be -6.478(2), -8.000(5), and -9.666(5) u Å2, respectively. The ΔI values suggest that only four hydrogen atoms are located out of the molecular skeletal plane of benzocyclobutene. The dipole moment (μa) was determined to be 0.56(5) D. © 1993 Academic Press, Inc.