5-MEMBERED CYCLIC-KETONES - MICROWAVE-SPECTRA OF ISOTOPIC SUBSTITUTEDCYCLOPENTENONES

The rotational spectra of cyclopentene-2-one-1 in the ground state and the first excited vibrational state of the ring puckering mode v(30) have been re-measured with improved accuracy in the range from 11-40 G Hz. One hundred and eleven and sixty nine rotational transitions with J quantum numbers up to fifty eight and forty eight, respectively, cou ld be assigned. The isotopomer 3-d-cyclopentene-2-one- 1 has been prep ared and its microwave spectra in the ground state and in the first an d second excited vibrational states of the ring puckering mode v(30) h ave been measured. We were able to assign 117 rotational transitions u p 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 als o 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 t hese D isotopomers, respectively, 87 and 119 rotational transitions of the ground state with J quantum numbers up to 65 were measured and as signed. The molecule appears to be very rigid-in 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-s symmetry of the molec ule is definitively confirmed. (C) 1997 Elsevier Science B.V.