W. Hutter et al., CROSS-CONJUGATED COMPOUNDS - MICROWAVE-SPECTRUM AND RING PLANARITY OF3-METHYLENE-1,4-CYCLOHEXADIENE, Journal of molecular structure, 319, 1994, pp. 73-83
The unstable 3-methylene-1,4-cyclohexadiene, an isomer of toluene, has
been prepared from benzoic acid. The hydrocarbon can be handled quite
easily in the solid state, and in the gas phase at low pressures. Rot
ational transitions have been measured from 12 to 40 GHz. Sixty-three
lines were assigned with J-quantum numbers up to 60. From the least-sq
uares fit with a standard deviation of 23 kHz the three rotational con
stants and all five quartic centrifugal distortion constants from Wats
on's A-reduction could be determined as A = 5177.8216(37) MHz, B = 261
3.1518(10) MHz, C = 1755.8422(9) MHz, DELTA(J) = 0. 1384(65) kHz, DELT
A(JK) = 0.135(16) kHz, DELTA(K) = 1.074(50) kHz, delta(J) = 0.0440(11)
kHz and delta(K) = 0.333(24) kHz (representation I(R) used). The dipo
le moment was found to be 0.8645(31) D from 32 frequency shifts in tot
al of the M components of the transition 8(35) <-- 7(34). The 6-monode
uterated species has also been prepared and its microwave spectrum mea
sured. Using Kraitchman's equations, the coordinates of the ring methy
lene hydrogens could be determined. The pseudoinertial defect was foun
d to be -0.1435(56) angstrom2 which proves that the molecule possesses
a planar ring. The results are compared with the data for 4,4-dimethy
l-2,5-cyclohexadien-1-one.