R. V. Galeev

Microwave Spectrum and Hindered Pseudorotation of Tetrahydrofuran

The microwave spectrum of the tetrahydrofuran (C4H8O) molecule in the ground state and eight excited states of hindered pseudorotation has been studied. A strong perturbation of rotational spectra has been found for three pairs of pseudorotational states, which is due to the vibrational-rotational interaction. To analyze the nonrigid spectra of these states we used the double resonance technique. Two hundred and sixty nine rotational and vibrational-rotational transitions corresponding to the μa and μc components of the dipole moment have been identified. The rotational constants have been determined along with the quartic constants of centrifugal distortion and the spectroscopic parameters of the interaction between the overall rotation and hindered pseudorotation. The splittings of three pairs of quasidegenerate vibrational levels have been calculated: Δ01 = 21,308.17 MHz, Δ23 = 61,205.28 MHz, Δ56 = 68,183 MHz. The potential function of hindered pseudorotation V(ϕ)=- 7.84(1-cos2ϕ)/2+36.10(1-cos4ϕ)/2 (cm–1) was found from the splittings. It is concluded that the molecule has a twisted conformation (C2 symmetry) in the states ν =0 and ν =1 of hindered pseudorotation and a bent conformation (Cs symmetry) in the states ν = 2 and ν = 3. The component of the dipole moment of the transition ‹ν = 2 |μc | ν = 3› = 0.57± 0.01D was determined from the Stark effect of the rotational transitions in the ν = 2, ν = 3 states.

Structure and internal rotation of methyl ethyl ketone

As a result of an investigation of the microwave spectrum of methyl ethyl ketone (CH~.COCH2CHs), from the triplet fine structure of the transition between the rotational levels of the vibrational ground state which are almost degenerate with respect to K, we have determined the height of the potential barrier to internal rotation V 3 = 795 • i0 cm -I of the methyl group furthest from the carbonyl. We give the rotational constants, the centrifugal distortion constants, and other spectroscopic parameters for methyl ethyl ketone in the first excited state of the torsional vibration of the skeleton. From measurements of the relative intensities of the transitions, we determined the frequency of the torsional vibration of the skeleton ~ = 80.4 • 6 cm -~, and found the height of the potentialbarrier V l ~ 5500 cm -I hindering internal rotation about the central C-C bond, We have observed strong interaction between the torsional vibration and the twisting vibration of the methyl group closest to the carbonyl group. We have concluded that the ground-state isomeric trans form predominates.

Microwave spectra ofs-cis-Glyoxal (CHO−CHO) molecules in excited vibrational states

The microwave spectra of s-cis-glyoxal molecules in the excited states of torsional (vt=1,2) and bending (vbend=1) vibrations have been studied. For the vt=1 state, the rotational constants have been refined and the quartic constants of centrifugal distorition have been determined. For the excited vt=2 and vbend=1 states, the rotational constants have found. For the ground vibrational state, the rotational constants and the quartic constants of centrifugal distortion have been refined. The vibrational frequencies have been determined from the relative intensities of rotational transitions.

Microwave spectrum, rotational parameters, and DFT geometry calculations for trans- and cis-isomers of 2,5-dimethyl-1,3-dioxane

The microwave spectrum of 2,5-dimethyl-1,3-dioxane is studied. The spectrum is identified to have the a and c type rotational transitions of the trans- and cis-isomers of the molecule. The experimental frequencies of the transitions are used to calculate the rotational constants and the quartic centrifugal distortion constants of the isomers. The dipole moments are determined. Quantum chemical calculations are performed by the B3PW91/aug-cc-pVDZ density functional method. The calculated results are compared with the experimental data. The equilibrium geometries of 1,3-dioxane and 2-methyl-, 5-methyl-, and 2,5-dimethyl-1,3-dioxanes are compared. It is found that the alkyl substitution leads to a change in the ring geometry

Microwave spectrum and DFT calculations of 4,4-dimethyl-1,3-dioxane

In the microwave spectrum of 4,4-dimethyl-1,3-dioxane, the rotational transitions of a, b, and c types with J ≤ 54 are identified in the ground vibrational state of the molecule in the frequency range of 12 GHz to 37 GHz. Rotational constants, quartic centrifugal distortion constants, and the dipole moment of the molecule are determined. The revealed transitions are found to belong to the chair conformer. The B3PW91/aug-cc-pVDZ method is used to calculate the geometric parameters of 1,3-dioxane, 4-methyl-1,3-dioxane, and 4,4-dimethyl-1,3-dioxane. Alkyl substitution is shown to cause changes in the geometry of the 1,3-dioxane core.

Vibrational Satellites and Pseudorotation in 2-Methyl-1,3-dioxolane

Vibrational satellites caused by pseudorotation are identified in the microwave spectrum of 2-methyl-1,3-dioxolane. The rotational constants of the satellites are determined up to state v = 6. Splittings between lower pseudorotational energy levels are determined by measuring the relative intensities of rotational transitions. An attempt is made to determine the form of the pseudorotation function of the molecule using the obtained data.

Microwave spectrum of 2-methyltetrahydrofuran

The microwave spectrum of 2-methyltetrahydrofuran in the ground vibrational state is studied. Rotational transitions belonging to one conformer of the molecule are found; no lines belonging to other conformers are detected in the spectrum. Such spectroscopic parameters of a molecule as rotational and quartic centrifugal distortion constants are determined using a set of identified rotational transitions in the quasirigid rotor approximation. Components of the dipole moment of a molecule in the principal axes system are determined from the Stark effect for four rotational transitions. Stable conformations of the molecule are sought by means of B3PW91 and B3LYP with aug-cc-pVXZ (X = D, T, Q) basis sets. A possible stable conformation of the molecule is discussed.

Microwave Spectrum and Dipole Moment of 1,3‐dioxolane in the Hindered‐Pseudorotation States v = 0, 1, 2, and 3

The microwave spectrum of 1,3‐dioxolane (C3H6O2) in the ground and first three excited states of hindered pseudorotation was studied. The transitions corresponding to the μb, μc, and μa components of the dipole moment were identified. The spectrum was analyzed using numerical diagonalization of the effective rotational Hamiltonian for four interacting states of hindered pseudorotation. The rotational constants, centrifugal distortion constants, the constants of interaction between general rotation and hindered pseudorotation, and the distances between the quasidegenerate vibrational levels Δ01 = 64840.5, Δ12 = 122231.7 and Δ23 = 119732.7 MHz are determined. From the Stark effect of microwave transitions, the dipole moment components (in Debye units) in the hindered‐pseudorotation states v = 0, 1, 2, and 3 are determined: 〈0|μb|0〉 = 〈1|μb|1〉 = 1.22, 〈2|μb|2〉 = 1.20, 〈3|μb|3〉 = 1.21, 〈0|μc|1〉 = 0.77, 〈2|μc3〉 = 0.66, and 〈1|μa|2〉 = 0.19.

Structure and spectra of 1,3,2-dioxaphospholenes. 1. Microwave spectra of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholene and its isotopomers in the ground and excited vibrational states

The microwave spectrum of 2-chloro-4,5-dimethyl-1,3,2-dioxaphospholene (1) was studied in the frequency range from 7 to 53 GHz. Rotational transitions of the parent molecule in the ground and eleven excited vibrational states and those of its mono-substituted 37Cl, 13CMe, and 13CCycle isotopomers in the ground vibrational state were identified. Rotational constants and partial rs-structure were obtained. The quartic centrifugal distortion constants, dipole moment components μa = 3.8D and μc = 0.24D (the total dipole moment μ is 3.81D), and the 35Cl quadrupole coupling constants were determined for the parent molecule. The fine structure of the microwave transitions in the parent molecule was analyzed under the assumption of noninteracting methyl groups. The height of the barrier to internal rotation (V30 = V03 = 665 cm–1) and the frequency of torsional vibrations (ν = 167 cm–1) were found. The frequencies of two lowest vibrational modes corresponding to deformation vibrations of the five-membered ring were estimated (ν∼100 cm–1) from the relative intensities of rotational transitions for different vibrational states.

Microwave spectrum, centrifugal perturbation, and dipole moment of acetyl chloride

An analysis of the microwave spectrum of acetyl chloride (12CH312C16O35Cl) in the ground vibrational state allowed us to determine the quartic constants of centrifugal distortion and to refine the rotational constants and the constants of quadrupole coupling of35Cl nuclei in this compound. The Stark effect of the 0–111 transition has been measured and analyzed. The components of the dipole moment have been determined: μa=1.047(10) D and μb=2.503(4) D. The total dipole moment of the moment of the molecule is 2.713(8) D.