Study Of Internal Rotation Research Articles

Effect of free valence on the characteristics of internal rotation in n-alkyl radicals

A study of internal rotation in the radicals n-CnH2n+1C·H2, (2 ≤ n ≤ 7) was carried out for the case of rotation around the bonds not including the radical center. 21 potential functions of internal rotation V(φ) were calculated. The coefficients in V(φ) were shown to depend only on the immediate environment at the bond of rotation. Characteristics of internal rotation in n-alkyl radicals were compared with related parameters of the corresponding alkane molecules. The generalized function Vav(φ) with the coefficients defined only by the position of the bond of rotation in the hydrocarbon chain and possessing the transposition property were proposed. The functions Vav(φ) were recommended for the simulation of the structure and properties of large molecules containing hydrocarbon fragments. This work continues a systematic study on the characteristics of the internal rotation in the n-alkane molecules and the groups containing free valence in n-alkyl radicals.

An analysis of the vibrational structure of high-resolution UV spectra and long-wave IR Fourier transform spectra in studies of internal rotation in molecules

The methods for analyzing the vibrational structure of high-resolution UV spectra and long-wave IR Fourier transform spectra in studies of internal rotation in α,β-unsaturated carbonyl compounds R4R3C=CR2-COR1 (R1 = F, Cl; R2 = R3 = R4 = H, CH3) are compared. These methods were found to give different experimental values for systems of torsional vibration energy levels up to high quantum numbers, torsional frequencies (0–1 transitions), and anharmonicity coefficients x 11 for trans and cis isomers of the same molecules in the ground electronic state (S 0). It was shown that the experimental technique for analyzing the vibrational structure of UV spectra excludes the hydrolysis of compounds under study. Taking into account Fermi resonance and numerous Deslandres tables constructed for trans and cis isomers provides reliable determination of values necessary for the construction of internal rotation potential functions, because they are multiply repeated in various Deslandres tables. An analysis of the vibrational structure of UV spectra gives more reliable V n internal rotation potential function parameters. The V n parameter values were substantiated by quantum-mechanical calculations performed by other authors.

Harmonic oscillator tensors. IV. A tensorial approach to internal rotations in molecules

A mapping of 2×2 matrices into the space of single boson operators is shown to lead to the angular momentum operators that give rise to irreducible tensors for the harmonic oscillator. The mapping may also be used to define an axis of quantization. A rotation about this axis induces a wave function and Hamiltonian that may be applied to the study of internal rotations in molecules. The example of a molecule containing two coaxial symmetric tops is presented as a case in point. The case of a potential with a high barrier leads to the approximation of an internal rotation as a torsional oscillator and, consequently, to torsional oscillator tensors whose properties are the same as those of the harmonic oscillator. The possibility of studying more complex potentials is discussed. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 65: 305–315, 1997

Study of internal rotation of the vinyl group in 1-, vinylpyridones by the AM-1 method

By the AM-1 method in the semirigid model approximation, the potential energy of internal rotation of the vinyl group has been calculated for 1-vinyl-2-pyridone, 1-vinyl-6-methyl-2-pyridone, and 1-vinyl-4-pyridone. The potential energy of internal rotation in the first and third of these molecules has two minima corresponding to torsion angles φ around the N-Cα bond approximately 0 and 180°, separated by barriers to internal rotation 3.99 and 2.94 kcal/mole, respectively. For the 1-vinyl-2-pyridone, the energy minimum at φ=180°, the s-cis(O) conformation, is 1.83 kcal/mole above the first minimum. For the 1-vinyl-6-methyl-2-pyridone, the torsion angles φ 0 and 180° correspond to energy maxima; the energy minima occur at φ 35° and 140°. In the harmonic oscillator approximation, the intervals of torsional vibrations of the vinyl group in these comopunds have been estimated. Data from the AM-1 calculation are in qualitative agreement with the available1H and13C NMR data on the structure of 1-vinyl-2-pyridone, 1-vinyl-5-methyl-2-pyridone, and 1-vinyl-4-pyridone.

Model calculations of chemical interactions. Part 1.—Intramolecular interactions and rotational barriers

A new procedure is introduced for the analysis of the effects of intramolecular interactions. Based on the most intuitive chemical picture of the energy differences between conformers, the procedure leads to explanations in terms of interactions between chemically meaningful subsystems into which the molecule can be conceptually partitioned, yet avoiding the concepts of antibond orbitals and bond–antibond interactions of the BO model. Use is made of the ab initio approximation with a minimal basis set of symmetrically orthogonalized hybrid AOs. Ethane, methylamine, methanol, propene, butadiene, glyoxal, hydrazine and hydroxylamine have been chosen as test molecules for the study of internal rotation.

A study of internal rotation in 2-furaldehyde through 13C relaxation times in the rotating frame

Carbon-13 relaxation times in the rotating frame were used to study the exchange between unequally populated rotamers of 2-furaldehyde. Calculated free activation energy and activation enthalpy are in good agreement with the results of 1H line shape analysis. Accuracy and reliability of this method in comparison with the line shape analysis is discussed.

Discovery of the gauche form in dichloroethane

Our study of internal rotation was carried out under the guidance of Professor San—ichiro Mizushima. Dipole moment measurements of 1,2-dichloroethane in non-polar solvents revealed a temperature dependence of the moment, which was interpreted as an indication of the existence of hindered rotation about the central CC bond, contrary to the original assumption of free rotation by van't Hoff and Le Bel. Raman Spectroscopy confirmed that the solid phase consists of the trans form only, whereas in the liquid and in the gas phases a second stable isomer coexists with the trans form. This second form was called > gauche< by Mizushima and its geometrical structure was established by electron diffraction. The potential function for internal rotation is considered with regard to its experimental determination and its interpretation by ab initio calculations.

On the use of the rotational isomeric state approximation in studies of internal rotation

A critical appraisal is made of the validity of the rotational isomeric state (RIS) approximation in studies of rotational isomerism, especially as far as the determination of energy differences for the stable conformers is concerned. By using simple model potential energy functions for internal rotation appropriate to some ethane derivatives, a comparison is made between the thermodynamic parameters that can be extracted from such potential functions and those obtained by applying the RIS method to continuum averaged values of conformation dependent properties. The effects due to the form of this conformation dependence, to the features of the potential energy curve, and to the temperature are discussed. The errors can be very large for realistic situations, and variable with temperature and with the property being studied; cases for which the errors are small are usually accidental.

A theoretical analysis of the conformations of model compounds of lignin. A study of internal rotation, the relative stability of the rotamers, and the intramolecular H-bond in the molecules of vanillin and m-methoxybenzaldehyde

A theoretical analysis of the conformations of model compounds of lignin. A study of internal rotation, the relative stability of the rotamers, and the intramolecular H-bond in the molecules of vanillin and m-methoxybenzaldehyde

Conformational behaviour of organic carbonyl compounds. Part 1. A molecular orbital approach to the study of internal rotation in conjugated aldehydes and ketones

Semi-empirical and ab initio MO methods are employed in a study of internal rotation of conjugated aldehydes and ketones. In general CNDO/2 does not provide a correct pattern for the energy as a function of the angle of internal rotation. The results from the semi-empirical PClLO method are more consistent with experiment. The calculated energy barriers are noticeably lower than the experimental ones, but roughly proportional. The energy barriers calculated by the ab initio MO approach with the minimal STO-3G basis set behave correctly as regards the relative stability of planar and perpendicular conformations, but quantitatively are not comparable with experimental values. The π-bond order for the C–C bond joining the carbonyl group to the unsaturated system for the planar conformation shows a linear correlation with the experimental free energy of activation for a large number of molecules and this is true of the values obtained both by CNDO/2 and by ab initio STO-3G.

Study of internal rotations in gramicidin S by means of carbon-13 spin-lattice relaxation measurements.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStudy of internal rotations in gramicidin S by carbon-13 spin-lattice relaxation measurementsAdam. Allerhand and Richard A. KomoroskiCite this: J. Am. Chem. Soc. 1973, 95, 25, 8228–8231Publication Date (Print):December 1, 1973Publication History Published online1 May 2002Published inissue 1 December 1973https://doi.org/10.1021/ja00806a003RIGHTS & PERMISSIONSArticle Views67Altmetric-Citations78LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (483 KB) Get e-Alerts Get e-Alerts

Hindered rotation in ortho-bis(dichloromethyl)benzenes

A study of internal rotation in ortho-bis(dichloromethyl)benzenes by 1H n.m.r. spectroscopy shows the presence of locked conformers on the n.m.r. time scale when these substituents are flanked on one or both sides by chlorine of additional dichloromethyl groups, and that in cases where a chlorine is substituted on both sides of two ortho-bis(dichloromethyl)groups ΔG‡ at Tc is 17·4–17·7 kcal mol–1.

A CNDO-INDO study of internal rotation in and the electronic structure of propylene

A CNDO-INDO study of internal rotation in and the electronic structure of propylene

The study of internal rotation in molecules by microwave spectroscopy

This article outlines some of the ways in which microwave spectroscopy can yield information pertaining to internal molecular movements. The main experimental features of the technique are summarized and the effect of hindered internal rotation of a methyl group on the overall rotational spectrum is briefly discussed. Illustrative examples from current research work include the determination of methyl barriers in substituted methyl formates, tunnelling of hydrogen in propargyl alcohol, cis and trans isomerism in acrylic acid and internal rotation of two methyl groups in isopropyl fluoride.

Internal rotation in dimethylaniline and para-substituted derivatives

A study of internal rotation in para-substituted dimethylanilines by 1H n.m.r. spectroscopy shows that the barrier to internal rotation of the dimethylamino-group is markedly dependent upon the nature of the para-substituent, and a Hammett correlation gives ΔG‡(at 133°K)= 5·1 (±1·0) kcal mol–1 for rotation in the parent compound dimethylaniline itself.

Molecular structure of 5,5′-bis-isoxazole. Part 2.—Non-bonded interaction and PPP calculations. Comparison with biphenyl and bipyridyl

Non-bonded interaction and PPP calculations using various refinements were accomplished on cis- and trans-conformations of 5,5′-bis-isoxazole, to study the problem of internal rotation of this molecule. For comparison purposes, 2,2′-bipyridyl and biphenyl were also treated by the same procedure. Results are discussed together with those of previous researches on biphenyl. With the simple PPP approximations, values of ΔEcis-trans of –30 and +5.5 kcal/mol were found for bis-isoxazole and bipyridyl, respectively, while the introduction of “penetration” integrals gave values of +10 and +20 kcal/mol, respectively. The strong dependence of these results upon the different approximations indicates that this approach, which had been satisfactory for biphenyl, cannot describe more complex problems arising in the study of internal rotation.

A Study of Internal Rotation in Ylides of Arsenic, Phosphorus, and Sulphur.

A Study of Internal Rotation in Ylides of Arsenic, Phosphorus, and Sulphur.

Vibrational spectroscopic studies of internal rotation of symmetrical groups. Part I. Evidence for a high barrier to internal rotation in methylpentacarbonylmanganese, CH3Mn(CO)5

Methylpentacarbonylmagnanese has been examined by i.r. spectroscopy in the vapour state, in solution, and as a solid in a potassium bromide disc. Particular attention has been paid to the antisymmetric methyl stretching vibration. Contrary to expectation on grounds of symmetry, which predicts a 12-fold barrier for internal rotation, there appears to be a high barrier of the methyl group estimated to be 2·7 ± 0·5 kcal. mole–1 in C2Cl4 solution. Intermolecular forces may also contribute to the barrier in solution, but there are indications that this is high in the vapour state also.Possible explanations for this unexpected result are considered in relation to the low-frequency vibrations of this molecule or in terms of dπ donation from metal atom to the methyl group.

Internal rotation in 2-dimethylaminopyridine

A study of internal rotation in 2-dimethylaminopyridine by 1H n.m.r. spectroscopy has yielded the activation parameters, ΔH‡= 7·6 (±1·0) kcal./mole and ΔS‡= 0·1(±6) e.u., for the rotation of the dimethylamino-group.

Torsion–Vibration–Rotation Interactions in Methanol. I. Millimeter Wave Spectrum

In a study of internal rotation in methanol, the millimeter wave spectra of CH3OH, CD3OH, and CH3OD have been investigated between 90 and 200 Gc/sec. In the analysis of the spectra, torsion–vibration–rotation interactions were treated as adjustable parameters in semiempirical formulas. Kivelson's formula for a-type ΔK = 0 transitions was tested over a wide range of quantum numbers. It reproduced the CH3OH and CD3OH spectra quite well, but the approximations used in the calculations appear to start breaking down for the larger asymmetry of CH3OD. For assignment of b-type ΔK = ± 1 transitions, a method was developed based on the wide spectral range of the millimeter wave spectrometer. Sufficient b-type data were obtained for CH3OH to permit a test of Kirtman's formula for origins of Q branches. Convergence difficulties in the Q-branch least-squares fit prompted a re-examination of the theory, which revealed an interesting linear relation coupling six of the parameters. This relation shows that for any molecule the torsional barrier terms V3 and V6, the two moments of inertia about the near-symmetry axis, and two of the adjustable interaction parameters cannot be independently determined from the spectrum of a single isotopic species. This casts some doubt on values previously reported for V6 in other molecules and adds further uncertainty to V3 determinations. The effective V3 obtained by ignoring torsion–vibration–rotation interactions was found to decrease slightly on deuteration, values of 375.6, 371.8, and 370.3 cm− 1 being obtained for CH3OH, CD3OH, and CH3OD, respectively. Although it is impossible to determine V6 unambiguously from the spectrum of CH3OH alone, a qualitative argument suggests that V6 lies between 0 and −0.8 cm−1. The geometry of the molecule has been completely determined from the experimental data.