Five-membered cyclic ketones: Microwave spectra of isotopic substituted cyclopentenones

Article abstract of DOI:10.1016/S0022-2860(97)00011-2

The rotational spectra of cyclopentene-2-one-1 in the ground state and the first excited vibrational state of the ring puckering mode υ₃₀ have been re-measured with improved accuracy in the range from 11-40 GHz. One hundred and eleven and sixty nine rotational transitions with J quantum numbers up to fifty eight and forty eight, respectively, could be assigned. The isotopomer 3-d-cyclopentene-2-one-1 has been prepared and its microwave spectra in the ground state and in the first and second excited vibrational states of the ring puckering mode υ₃₀ have been measured. We were able to assign 117 rotational transitions up to J = 69 in the ground state and 63 and 44 transitions with J quantum numbers up to 40 and 18, respectively, for the excited states. We also prepared 4-d-cyclopentene-2-one-1 and 5-d-cyclopentene-2-one-1 in an isotopomeric mixture together with the parent molecule. For each of these D isotopomers, respectively, 87 and 119 rotational transitions of the ground state with J quantum numbers up to 65 were measured and assigned. The molecule appears to be very rigidin all cases the quartic centrifugal distortion constants could be determined with remarkable accuracy, whereas only for two fits were one and two sextic constants needed, despite the high J and K values. The C, symmetry of the molecule is definitively confirmed.