Microwave spectrum, structure, dipole moment, and internal rotation of the GT isomer of fluoromethylethylether
Abstract
Microwave spectra of fluoromethylethylether and its 13 isotopically substituted species have been measured. The rs structure of the GT isomer of this molecule was determined from the observed moments of inertia. The structural parameters obtained are roughly close to those of fluoromethylmethylether and the GT isomer of chloromethylethylether. The dipole moments and their directions in the molecule were determined from the Stark effect measurements of several low-J transitions for the normal and two deuterated species. The dipole moment of the normal species was found to be 1.806 ± 0.012 D, making angles of 136°50′ and 107°40′ with the CF and FCH2O bonds, respectively. From the A-E splittings of the spectra in the first excited methyl torsional state, the barrier to internal rotation of the methyl group was calculated to be 3150 ± 50 cal/mole in the one-top approximation.
References (7)
- M. Hayashi et al.
J. Mol. Struct.
(1979) - M. Hayashi et al.
J. Mol. Spectrosc.
(1979) - M. Hayashi, J. Nakagawa, and H. Kato, J. Mol. Spectrosc., in...
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Diisopropylethylamine mono(hydrogen fluoride) for nucleophilic fluorination of sensitive substrates: Synthesis of sevoflurane
2001, Journal of Fluorine ChemistryDiisopropylethylamine mono(hydrogen fluoride) (8), which can be prepared by addition of two equivalents of diisopropylethylamine to the complex diisopropylethylamine tris(hydrogen fluoride) (7), is shown to be an effective and selective nucleophilic fluorinating reagent when applied to halogen-exchange reactions of chloromethyl ethers, in particular the conversion of 1,1,1,3,3,3-hexafluoroisopropyl chloromethyl ether (3) to the volatile anesthetic sevoflurane (1,1,1,3,3,3-hexafluoroisopropyl fluoromethyl ether). The amine portion of the reagent does not react with the starting material to give a troublesome quaternary ammonium salt, as is the case for the species formed by addition of two equivalents of triethylamine to triethylamine tris(hydrogen fluoride). These particular chloromethyl ether substrates require a 1:1 stoichiometry of diisopropylethylamine to hydrogen fluoride to give useful rates of reaction and yields when solventless conditions are desired. Two other complexes, diisopropylethylamine bis(hydrogen fluoride) and 7, are ineffective for conversion of 3 to sevoflurane.
Chapter 3 The quest for the equilibrium structure of molecules
1999, Vibrational Spectra and StructureThis chapter explores that the determination of molecular structures has been one of the objectives of high resolution spectroscopy for a long time. This technique, together with gas phase electron diffraction, is the only practical method available to study structures of molecules in the gaseous state. In that state at sufficiently low pressures, molecules are free from interactions with other species and can therefore be studied isolated from the environment. It discusses that modern high resolution molecular spectroscopy has a tremendous resolving power and precision. Conventional Stark effect modulated microwave spectroscopy has a typical resolution of 1 in 105 and precision of 1 in 106. A similar precision is achieved by high resolution Fourier transform infrared spectroscopy. Fourier transform microwave spectroscopy and laser based infrared spectroscopy have a precision close to 1 in 108. If these spectroscopic methods are coupled with the supersonic molecular beam technique, the resolution approaches 1 in 107. The chapter also discusses the theoretical models for fairly rigid molecules. With these models, the spectra observed for such molecules can be reproduced within the experimental precision. Many fitting parameters of these models—the spectroscopic constants—are obtained with high precision. Among them are the rotational constants, which sometimes have 8 or more significant digits. The chapter reviews the methods and techniques that are used to determine gas phase molecular structures from high resolution spectroscopic data. Principal techniques to obtain structures of molecules in the gas phase, electron diffraction are also discussed.
Ab initio rotational barriers and solvation free energies of fluorinated dimethyl ethers
1996, Journal of Molecular Structure: THEOCHEMHalogenated ethers are a significant class of inhalation anesthetics, but current molecular mechanics packages have not been parameterized to deal with this class of compounds. Here a first step is made towards the determination of these parameters for halogenated ether anesthetics by calculation of the -CH3, -CF3, -CH2F, and -CHF2 rotational barriers in a series of ten fluorinated dimethyl ethers. With the 6–31G∗∗ basis set, the shape and magnitude of the rotational barrier was found to be dependent on the number and location of fluorine substituents. Inceasing the number of fluorine substituents on the opposite methyl group leads to a decrease in the rotational barrier. With zero, one, two, and three fluorines on the opposite methyl group, the -CH3 rotation barrier was found to be 2.53, 1.76, 1.02, and 1.13 kcal mol−1, respectively, and the -CF3 rotation barrier was found to be 2.64, 2.03, 1.88, and 1.03 kcal mol−1, respectively. Similar trends were noted for the gauche-trans, trans-gauche, and gauche-gauche barriers for the -CH2F and -CHF2 groups. Inclusion of electron correlation at the MP2/6–31G∗∗//6–31G∗∗ level had negligible effect on the energy of the minimum and maximum energy conformers of the analogs.
The calculations show that increasing fluorine substitution has a pronounced effect in opening the COC bond angle, presumably due to lone pair-lone pair repulsions. The central COC bond angle varied between 114 ° and 131 ° for the series, a range of values much larger than the COC angle of 107 ° given in MM3. The gas phase ab initio energy increases as the C OC bond angle increases. Fluorine substitution on one methyl group decreases the OC bond length of the carbon to which the fluorine is attached and increases the length of the other OC bond. Increasing the number of fluorine substituents on the same carbon leads to a more pronounced effect.
Inclusion of solvation free energy, calculated by the Induced Polarization Charge Boundary Element Method, was found to have a negligible effect on the potential energy surface. Further, the difference between the calculated electrostatic contribution to the hydration free energy and enthalpy was on the order of 3%–4%.
Microwave Spectrum, Structure, and Nuclear Quadrupole Coupling Constant Tensor of Iodomethyl Methyl Ether
1995, Journal of Molecular SpectroscopyMicrowave 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 rs 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 χab, χac, and χbc, 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.
Computation of O-C-F and N-C-F systems: AB-initio calculations and a MM2 parameterization study. Theory vs. experiment
1993, TetrahedronA parameterization scheme of Allinger's MM2 force field for the anomeric effect in O-C-F and N-C-F systems is presented. The scarcity of experimental data, in particular for the N-C-F case, dictated the use of ab-initio calculations to account for the energetic and structural manifestations of the effect. The resulting modified force field was tested against available X-ray, microwave and NMR results leading to a very good agreement between calculations and experiment. In addition, ab-initio results were used to demonstrate the role of the anomeric effect in lowering barriers to N-inversion and elevating barriers for rotation around single CN bonds. The results for the fluoro compounds, when juxtaposed to other systems, provide a complete treatment of the anomeric effect for the first row elements.
Microwave spectrum and nuclear quadrupole coupling constant tensor of iodomethyl methyl ether
1988, Journal of Molecular SpectroscopyMicrowave 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 χzz = −1672.70 ± 0.46 MHz, ηz = 0.0569 ± 0.0031, and (θza, θzb, θzc) = (28°34′, 62°54′, 98°23′) for the normal species which indicate the χ tensor is slightly distorted from the cylindrical symmetry around the CI 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, χab.