Microwave spectrum, structure, dipole moment, and internal rotation of methylpropargylether

doi:10.1016/0022-2852(80)90028-4

Journal of Molecular Spectroscopy

Volume 84, Issue 2, December 1980, Pages 362-374

https://doi.org/10.1016/0022-2852(80)90028-4 Get rights and content

Abstract

Microwave spectra of methylpropargylether and its nine isotopically substituted species were measured. The plausible structure of this molecule was determined from the observed moments of inertia. The r_s structural parameters of the OCH₃ part of the molecule could be obtained and were compared with the corresponding parameters of the analogous molecules. The dipole moment and its direction in the molecule were determined by Stark-effect measurements. The barrier to internal rotation of the methyl group was determined from the A-E splittings of the spectra reported by K. M. Marstokk and H. Møllendal (J. Mol. Struct. 32, 191–202 (1976) taking into account the coupling effect of the skeletal torsion.

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Cited by (14)

Microwave Spectrum, Structure, and Nuclear Quadrupole Coupling Constant Tensor of Iodomethyl Methyl Ether
1995, Journal of Molecular Spectroscopy
Microwave spectra of iodomethyl methyl ether and its 10 isotopic species have been measured. A least-squares analysis of the observed frequencies gave rotational and quartic centrifugal distortion constants and all the components of the nuclear quadrupole coupling constant tensor. The r_s structure has been well established from the moments of inertia calculated from the observed rotational constants. The observed nuclear quadrupole coupling constant tensor in the inertial principal axes system could be transformed into that in its own principal axes system. The directions of the χ principal axes in the molecule were found to be closely related to the signs of three off-diagonal χ components in the inertial principal axes system which could not be determined by the least-squares fit of the observed frequencies. The signs of the three off-diagonal χ components were concluded to be (+, +, −) for χ_ab, χ_ac, and χ_bc, respectively. The z axis of the principal χ system is roughly along the CI bond, while the x axis is no longer in the OCI plane but is inclined by about 6°30′ toward the side where the CH₃ group exists. The molecular structure and nuclear quadrupole coupling constant tensor of the present molecule were compared with those of the other halomethyl ethers, alkyl halides, and alkyl ethers.
Conformational stability, barriers to internal rotation, ab initio calculations and vibrational assignment of methyl propargyl ether
1994, Journal of Molecular Structure
The Raman spectra (3400 to 10 cm⁻¹) of gaseous, liquid and solid and the infrared spectra (3500 to 35 cm^{−1) of gaseous and solid methyl propargyl ether, HCCCH₂OCH₃, have been recorded. Furthermore, the far-infrared spectrum of the gas has been recorded in the region of 370 to 30 cm⁻¹ at a resolution of 0.10 cm⁻¹. From the vibrational spectrum two conformers have been identified in the fluid phases at ambient temperature with the gauche rotamer the more stable conformer and the only one present in the annealed solid. The fundamental asymmetric torsions of the gauche and trans conformations have been observed at 113.2 and 102.0 cm⁻¹, respectively, with the gauche form having three excited state transitions falling to lower frequency. From these data, the asymmetric torsional potential function has been obtained with the following coefficients: V₁ = 325 ± 24, V₂ = −662 ± 23, V₃ = 1149 ± 14, V₄ = −102 ± 6 and V₆ = −46 ± 6 cm⁻¹. From this potential function, the trans to gauche, gauche to gauche and gauche to trans barriers are determined to be 664, 1831 and 1021 cm⁻¹, respectively, with an enthalpy difference between the conformers of 357 ± 61 cm⁻¹ (1021 ± 174 cal mol−1} and the gauche conformer the more stable form in the gas. The enthalpy difference has been determined experimentally for the liquid from the variable-temperature studies of the Raman spectrum and a value of 153 ± 10 cm−1 (437 ± 29 cal mol⁻¹) has been obtained with the gauche form again the more stable rotamer. The methyl torsional transitions of the gauche and trans rotamers have been observed at 166.0 and 214.2 cm⁻¹, respectively, and on the basis of the one-dimensional model the barrier to internal rotation of the methyl group is determined to be 707 ± 45 cm⁻¹ (2.02 kcal mol⁻¹) and 991 ± 67 cm⁻¹ (2.83 kcal mol⁻¹) for the gauche and trans conformers, respectively. A complete vibrational assignment is proposed for a gauche/trans equilibrium in the gas and liquid phases. The structural parameters, conformational stability, barriers to internal rotation and fundamental vibrational frequencies which have been determined experimentally are compared to those obtained from ab initio calculations employing the RHF/4–31G*, RHF/6–31G*, MP2/6–31G* and/or MP2/6–31++G** basis sets. These results are compared to those obtained for some similar molecules.
Far-IR spectra, barriers to internal rotation, r<inf>0</inf> structural parameters and ab initio calculations of chloromethyl methyl ether
1993, Spectrochimica Acta - Part A Molecular Spectroscopy
The far-IR spectra from 350 to 50 cm⁻¹ of gaseous chloromethyl methyl ether, ClCH₂OCH₃, along with three of the deuterium isotopomers, have been recorded at a resolution of 0.10 cm⁻¹. The fundamental asymmetric torsional and methyl torsional modes are extensively mixed and have been observed at 180 and 133 cm⁻¹, respectively. An estimate is given for the potential function governing the asymmetric torsion. On the basis of a one-dimensional model the barrier to internal rotation of the methyl moiety is determined to be 556 ± 5 cm⁻¹ (1.59 ± 0.01 kcal mol⁻¹). Utilizing previously reported rotational constants for seven isotopomers, r₀ structural parameters are determined. The heavy atom parameters (distances in ångströms angles in degrees) are: r(C₁−Cl) = 1.818 ± 0.003; r(C₁−O) = 1.371 ± 0.004; r(C₂−O) = 1.430 ± 0.001; ∢ClC₁O = 113.01 ± 0.07;∢ClOC₂ = 114.03 ± 0.10 and dihedral ClC₁OC₂=70.20 ± 0.15. A complete vibrational assignment is given for the ClCD₂OCD₃ molecule. The fundamental vibrational frequencies, barrier to internal rotation and structural parameters which have been obtained experimentally are compared with those obtained from ab initio Hartree-Fock calculations employing the 3–21G^* and 6–31G^* basis sets along with the 6–31G^* basis set with electron correlation at the MP2 level. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.
Microwave spectrum and nuclear quadrupole coupling constant tensor of iodomethyl methyl ether
1988, Journal of Molecular Spectroscopy
Microwave spectra of iodomethyl methyl ether (CH₃OCH₂I) and its two deuterated species have been measured. A least-squares analysis for the observed frequencies gave rotational, centrifugal distortion constants and all the components of the nuclear electric quadrupole coupling constant tensor of the molecule. From the rotational constants obtained, a plausible structure of this molecule was estimated to be the gauche form with about 73°30′ for the dihedral angle value. Transformation of the nuclear electric quadrupole coupling tensor χ into its own principal axes system gave χ_zz = −1672.70 ± 0.46 MHz, η_z = 0.0569 ± 0.0031, and (θ_za, θ_zb, θ_zc) = (28°34′, 62°54′, 98°23′) for the normal species which indicate the χ tensor is slightly distorted from the cylindrical symmetry around the CI bond. In the course of the measurements, a forbidden transition of 9₁₈ ← 7₂₅ and irregular patterns of the multiplet for the 8₂₆ ← 8₁₇ and 9₂₇ ← 9₁₈ transitions were found and understood as the result of accidental near degeneracy of the 9₁₈ and 8₂₆ levels which are connected by the energy matrix element containing the largest off-diagonal χ element, χ_ab.
Microwave spectrum and structure of cis-methyl vinyl ether
1985, Journal of Molecular Structure
Microwave spectra of cis-methyl vinyl ether and its 14 isotopically substituted species have been measured. The r_s structure of this isomer has been determined from the observed moments of inertia. The dipole moment and its direction in the molecule have been determined by Stark effect measurements of the spectra for three isotopic species. The barrier to internal rotation of the methyl group has been determined from the A-E splittings of the spectra in the excited methyl torsional states. The structure of the present isomer is discussed in comparison with those of the analogous molecules. An ab initio MO calculation has been carried out for the structure obtained, the discussions being extended to the direction of the dipole moment in the molecule.
Microwave spectrum, structure, dipole moment and internal rotation of isopropyl methyl ether
1984, Journal of Molecular Structure
Microwave spectra of isopropyl methyl ether and its three deuterated substituted species have been measured and assigned for the isomer with C₁ symmetry. A plausible structure was proposed from the moments of inertia obtained. Two CCO angles at the gauche and trans positions with respect to the OCH₃ group differ by 6° with each other and the isopropyl group inclines to the lone pair electrons on the oxygen atom. The dihedral angle between the COC and OCC planes at the gauche position is 71.9°. The barrier to the internal rotation of the methoxy group is 17 25 cal mol⁻¹, which is much lower than those of n-alkyl methyl ethers. The direction of the dipole moment nearly coincides with the bisector of the COC angle and lies in the COC plane.

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Microwave spectrum, structure, dipole moment, and internal rotation of methylpropargylether

Abstract

J. Mol. Spectrosc.

J. Mol. Struct.

J. Mol. Struct.

J. Mol. Struct.

J. Mol. Spectrosc.

J. Mol. Struct.

Chem. Lett.

Chem. Lett.