Vibrational spectra of methylenecyclopentane, methylenecyclopentane-2,2,5,5-d4 and methylene-d2-cyclopentane-2,2,5,5-d4

Structures and Conformations of Non-Rigid Molecules

“…The molecularconstantsare.presented in table 8 and compared with (i) the values deduced from a global fit including our millimeter wave transitions and the data from Crofton et al [9], (ii) the values obtained,bY'Crofton et al [9], (iii) the ab initio parameters of Grev and Schaefer [77]. All these results are rematkably consistent and confirm the detection of the nonclassical bridged structure ofC2H3+.…”

“…The fundamental frequencies for these two modes are changed little in the two states since the ring has a similar twisted ring conformation for each state, However, as shown in Table 4, the data for the ring modes indicates that in the SI state there is a barrier to pseudorotation of about 550 cm,l, This value is a measure of the energy difference between the lower energy twisted conformation and the bent structure, The twisting data suggest that the barrier to planarity (the energy difference between the planar and twisted forms) may exceed 1000 cm,l. Thus, the two-dimensional potential energy surface for the out-of-plane ring modes is substantially different from that proposed for the ground state [77]. …”

“…We predicted the millimeter wave spectrum by using the constants of Crofton et al [9], including the A value and we noticed that only few lines were sufficiently intense to be observed in the laboratory. We fixed its value to that obtained ab initio by Grev and Schaefer [77]. We tried to observe it in a negative glow discharge (1=6 rnA) in a mixture of C2H2fH2f Ar with partial pressures of respectively 20!2/4 mtorr measured at room temperature, the cell being cooled at liquid nitrogen temperature.…”

Thermal Chemistry of 1-Methyl-1-Cyclopentene and Methylene Cyclopentane on Pt(111) Surfaces: Evidence for Double-Bond Isomerization

“…The more intense modes in this temperature range are those at 2860 and 2945 cm -1 , which are assigned to the CH 2 symmetric (in-plane) and asymmetric (out-of-plane) vibrations, respectively. 29 Also, no shifts in peak positions are observed for MeCp with increasing temperature, indicating a lack of rehybridization. The modes observed at 200 K are still seen up to 275 K, but new bands also grow about 2960, 2930, and 2910 cm -1 indicative of the formation of a second species.…”

Secondary deuterium isotope effects on both rate and product determining steps in the thermolysis of 4-methylene-1-pyrazoline

“…Using the data in Table 5 and assuming the C-N stretch to be the reaction coordinate we have evaluated the change in zero point energy for the series 10-14. As our model for the transition state we considered the change of the sp3 a-methylene group to the sp2 methylene of the diazenyl radical 26 using the methylenecyclopentane (27) and 28 assignments of Malloy et al (16). The predicted changes in zero point energies are summarized in Tables 6 and 7 for both the one-bond cleavage, path A, and the two-bond cleavage, Path B.…”