The Microwave Spectrum of 1-Chloro-2-methylpropene

A touch of lavender: gas-phase structure and dynamics of the monoterpene linalool validated by microwave spectroscopy

“…The barrier height to internal rotation of methyl group 2 was determined to be 400.20(64) cm À1 , higher than the value of 304.34(2) cm À1 found for the trans methyl group in 1-chloro-2methylpropene (1C2MP). 12 Furthermore, only in a few transitions small splittings due to internal rotation of methyl group 3 could be resolved, i.e. the barrier of this methyl group is also higher than that of the cis methyl group in 1C2MP (928.0(17) cm À1 ).…”

“…In a second step, we assumed the barrier to internal rotation of methyl group 2 to be 300 cm -1 , similar to the value found for the trans-methyl group in 1-chloro-2-methylpropene. 12 The angles between the internal rotor axis and the principal axes of inertia were taken from the optimized geometry. Due to internal rotation of methyl group 2, all lines in the spectrum should split into doublets, which are called the A and the E species.…”

“…The -CCH3OH-methyl group should have a high barrier over 1000 cm −1 , since no splittings 60 from such a methyl group were reported in similar cases like isopropanol 10 and 2-butanol. 11 From a study on 1-chloro-2methylpropene, 12 we know that the barriers of the trans and cis methyl groups fixed to the double bond are 304.34(2) cm −1 and 928.0(17) cm −1 , respectively. Therefore, we expected to be able to resolve the splittings due to internal rotation of these two methyl groups also in the microwave spectrum of linalool.…”

Structural and Torsional Properties of o-Cresol and o-Cresol-OD as Obtained from Microwave Spectroscopy and ab Initio Calculations

“…Due to the promising results of our recent work (24,25) we calculated the barrier to internal rotation with the Gaussian 94 (26) ab initio package. Second order Møller-Plesset perturbation theory (MP2) was used with the 6-311G * * basis set.…”

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

“…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.…”