Millimeterwave rotational spectrum and internal rotation in o-chlorotoluene

Asymmetric-top molecules containing one methyl-like internal rotor: Methods and codes for fitting and predicting spectra

“…The Woods method had various ''filiations". It was later extended by van Eijck et al [32], Maes et al [33], Nair et al [34] for the one-top internal rotors, and by Vacherand et al for two-tops [35]. Finally the Woods method was also used in the XIAM modern code written by Hartwig and Dreizler at Kiel, which can calculate line positions and for one, two or three internal rotors [36].…”

Molecular structure and vibrational spectra of o-chlorotoluene, m-chlorotoluene, and p-chlorotoluene by ab initio HF and DFT calculations

“…the other C-C bonds on the benzene ring could be attributed to the steric effect of the larger methyl group. Gerhard et al [8] have calculated the structural parameters of OCT at MP2 level. The length of the C-C bond connecting the methyl group and benzene ring is 1.50Å, the length of the C-Cl bond is 1.74Å, and the length of the C-C bonds of the benzene ring varies from 1.39 to 1.40Å.…”

“…They also calculated the bond lengths, bond angles and dihedral angles in OCT using MP2/6-311+G(2df,2p) method. Recently, Nair et al [8] investigated the internal rotation of OCT based on its millimeterwave rotational spectrum.…”

The microwave spectrum of methyl chlorodifluoroacetate: Methyl internal rotation and chlorine nuclear electric quadrupole coupling

“…Arguments explaining this different behaviour have invoked steric factors [8]. An extreme case of barrier increase is seen for toluene [40] versus o-chlorotoluene [9,10], see Table 4. A rough calculation shows that the distance from the methyl carbon to the hydrogen in the ortho position of toluene is 2.7 Å.…”

“…However, only a few molecules of this type have been examined at a high enough resolution in which internal rotation fine structure and chlorine nuclear quadrupole splittings have been observed. Examples include acetyl chloride [3], 1-chloro-1-fluoroethane [4], 1-chloro-1, 1-difluoroethane [5], cis-chloropropene [6], cis-1-chloro-2-methylpropene [7], 1-chloro-2-nitrosopropene [8], and o-chlorotoluene [9,10]. A comparison of methyl group internal rotation barriers in mono-chlorinated species and non-chlorinated analogs shows that the presence of Cl can (i) increase the barrier to internal rotation when the Cl is close to the methyl rotor, but can also (ii) decrease the barrier to internal rotation when the Cl is far away from the methyl rotor.…”