MICROWAVE-SPECTRUM AND STRUCTURE OF 3,3,4,4-TETRAFLUOROCYCLOBUTENE

The microwave spectra of the normal, deuterated (d2), and C-13 isotopic species of 3,3,4,4-tetrafluorocyclobutene were assigned. The rotational constants and selection rules are consistent with C2-upsilon symmetry. The structural parameters are d(C = C) = 1.349 (6) angstrom, d(HC-CF2) = 1.501 (6) angstrom, d(F2C-CF2) = 1.539 (6) angstrom, d(C-H) = 1.080 (1) angstrom, d(C-F) = 1.358 (2) angstrom, angle C = C-C = 93.6 (2)-degrees, angle C-C-C = 86.3 (2)-degrees, and angle FCF = 106.2 (2)-degrees. The dipole moment is 3.43 (2) D. The F2C-CF2 bond is significantly shorter than the analogous bond in cyclobutene, a change that is consistent with the effect of fluorine substitution in C3 ring systems.