Rotation In Ethane Research Articles

An unusual rotational distortion in an [(η-indenyl)RhL2] complex: molecular structures of [(η-1,2,3-Me3C9H4)Rh(η-C2H4)2] and [(η-C9H7)Rh(CO)2

The molecular structures of [(η-1,2,3-Me3C9H4)Rh(η-C2H4)2] and [(η-C9H7)Rh(CO)2], barriers to hindered ethylene rotation in a series of indenyl rhodium bis(ethylene) complexes bearing different degrees of indenyl-ring methylation, and the barrier to hindered indenyl-ring rotation in [(η-1-MeC9H6)Rh(CO)2] are reported.

Theoretical investigations of the nature of intramolecular interactions

The description of intramolecular interactions by a single-determinant wave function of non-orthogonal, strictly local, molecular orbitals (NOLMOs) is improved by the admission of electron charge transfer into anti-bonding orbitals. An energy decomposition scheme in terms of quasiclassical (overlap independent), interference (overlap dependent) and charge transfer components is outlined. The formalism is applied to the study of the barrier to internal rotation in ethane. It is found that vicinal CH-CH′ interactions and non-additivity effects on geminal CH-CH interactions constitute the two major contributions to the barrier.

Energy dissipation mechanism of the optically excited molecules in solvents: A trajectory study for a photoisomerization process of the π-conjugated molecule in Ar and water

The energy dissipation mechanism of an optically excited molecule in solution is studied by using a classical molecular dynamics (MD) calculation. We chose ethylene in Ar or water as a model system and perform the MD calculation to analyze the solvent response to the optically excited ethylene motions that are large in magnitude and high in frequency. It is found that the energy dissipation is very fast; it is in the order of a picosecond in water and of a few to a few tens of picoseconds in Ar. The energy decay rate strongly depends on each ethylene mode and on the nature of solvent–solvent interaction. Due to the characteristic form of water–water interaction, that is strong and sensitive to the mutual geometrical changes, a large water kinetic fluctuation occurs. The ethylene motions couple to this water fluctuation efficiently transferring the ethylene energy to the water libration energy, that is immediately distributed into the various inter- and intrawater modes. A multistep collision process leading the energy flow from the ethylene internal vibration→the ethylene rotation→the solvent molecule motion, not accounted for in the gas-like models such as isolated binary collision model, is a pathway for the fast energy dissipation in Ar and water. We also employ a simple model of an oscillator in Ar to make a detail analysis of the energy decay mechanism, especially of its dependence on the oscillator amplitude, the solvent–solvent interaction, and the solvent density.

A rotationally invariant orbital transformation

A new transformation which predicts molecular orbitals at one molecular geometry from those at another is presented. Unlike other transformations, this one maintains invariance when the geometry change reduces to a pure rotation. The transformation is compared to two others for the internal rotation in ethane using the closed shell canonical Hartree–Fock molecular orbitals and the STO-3G basis. In additon to predicting orbitals that are independent of how the internal rotation is specified, the transformation gives remarkably accurate results.

Coulombic models in chemical bonding. III: Barrier to internal rotation in ethane

In this paper, a problem of long standing will be considered: the barrier to internal rotation in ethane.

Dynamic 1H NMR spectroscopy of η2‐ethylene transition metal complexes

AbstractThe low‐temperature 1H NMR spectra of bis(ethylene)trimethylphosphinenickel (1), η5‐cyclopentadienyl(ethylene)methylnickel (2a), bis(ethylene)‐η5‐cyclopentadienylcobalt (2b), [bis(1‐ethyl‐2,4,6‐triphenylphosphorinyl)nickel]P,P′‐nickel(ethylene) (3) and η5‐cyclopentadienyl(ethylene)hydrido(triphenylphosphine)ruthenium (4) exhibit {AA′B′B} (1) {ABB′A} (2a and 2b), {ABA′B′} (3) or {ABCD} (4) spin patterns, respectively, for the complexed ethylene. A full line shape analysis including all the proton couplings was performed for the ethylene rotation in 1, 2a and 2b. In addition to olefin rotation, a reversible intramolecular β‐H‐elimination was confirmed for 4 by magnetization transfer experiments.

The barrier to internal rotation in ethane

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe barrier to internal rotation in ethaneRussell M. PitzerCite this: Acc. Chem. Res. 1983, 16, 6, 207–210Publication Date (Print):June 1, 1983Publication History Published online1 May 2002Published inissue 1 June 1983https://doi.org/10.1021/ar00090a004RIGHTS & PERMISSIONSArticle Views1396Altmetric-Citations100LEARN 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 (610 KB) Get e-Alerts Get e-Alerts

Density-difference maps in quantum chemistry

Electron density-difference maps, used to study the changes that occur when a molecule changes its state or when the nuclei of a molecule change their relative positions, are generally useful only if the atomic densities cancel when one molecular density distribution is subtracted from the other. When, as in the case of the nonrigid internal rotation in ethane, such a cancellation of atomic densities is not possible the method of simple subtraction is no longer appropriate. It is shown that useful density-difference maps can nevertheless be obtained, when the changes in geometric parameters are small, by the calculation of two generalized density-difference functions: a point difference function which allows a comparison of the densities at corresponding points in the two systems, and a volume difference function to compare the amounts of charge in corresponding regions. The method is illustrated by consideration of a change in bond length of the nitrogen molecule and by the nonrigid internal rotation in ethane.

Bond-orbital analysis of rotation barriers. Polarization and delocalization effects in ethane

Ab initio calculations of the barrier to rotation in ethane using a one-configuration wavefunction of non-orthogonal bond orbitals are supplemented by small correction terms accounting for electron delocalization. These corrections are introduced through a second-order perturbative CI calculation in terms of non-orthogonal configurations constructed from all the single excitations to localized antibonding orbitals. Besides being very close to those obtained from the full MO wavefunction, the results allow a clear-cut analysis of the main factor contributing to the barrier. Similar calculations using different types of orthogonalization show much larger second-order contributions to the barrier because of the need to correct for the large errors in the one-configuration calculation resulting from the forced orthogonalization of the basis set.

ChemInform Abstract: BARRIER TO INTERNAL ROTATION IN ETHANE FROM THE MICROWAVE SPECTRUM OF CH3CHD2

Chemischer InformationsdienstVolume 10, Issue 48 Physical Organic Chemistry ChemInform Abstract: BARRIER TO INTERNAL ROTATION IN ETHANE FROM THE MICROWAVE SPECTRUM OF CH3CHD2 E. HIROTA, E. HIROTASearch for more papers by this authorS. SAITO, S. SAITOSearch for more papers by this authorY. ENDO, Y. ENDOSearch for more papers by this author E. HIROTA, E. HIROTASearch for more papers by this authorS. SAITO, S. SAITOSearch for more papers by this authorY. ENDO, Y. ENDOSearch for more papers by this author First published: November 27, 1979 https://doi.org/10.1002/chin.197948057AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume10, Issue48November 27, 1979 RelatedInformation

Barrier to internal rotation in ethane from the microwave spectrum of CH3CHD2

Rotational spectra of CH3CHD2 were observed by using a source-modulation microwave spectrometer. Of 26 observed transitions, 16 showed splittings due to internal rotation. An analysis of the observed spectra, which utilized an internal axis method modified to include centrifugal distortion effects, gave the following results: A=60 809.592 (59) MHz, B=17 770.87 (16) MHz, C=17 084.84 (16) MHz, F=257.70 (35) GHz, and V3=2.8783 (28) kcal/mole, with 2.5 times standard errors in parentheses. In the analysis V6=0 was assumed, and D, a constant associated with a cross product of inertia, was fixed to a calculated value. When the uncertainty in D is taken into account, the error of V3 increases to 0.0029 kcal/mole. Effects of the molecular vibrations on the barrier are discussed briefly.

The uniaxial rotation of ethylene adsorbed by sodium 13X zeolite

Measurements of quasi-elastic neutron scattering have enabled us to characterize the rotational and translational dynamics of an ethylene molecule adsorbed in sodium zeolite 13X. We find that a model for the scattering describing the motion in terms of 180° jump rotation about an axis perpendicular to the surface passing through the mid-point of the molecule satisfactorily explains the data. Uniaxial rotation about the other principal axes of the molecule is incompatible with our measurements. From this model we deduce that the molecule executes about 20 rotational jumps between each translation step.

Ethylene displacement reactions of h 5-indenylbis- (ethylene)rhodium(I)

The barrier to ethylene rotation in h 5-indenylbis(ethylene)rhodium I is lower than that in the analogous h 5-cyclopentadienyl complex and ethylene is readily displaced by carbon monoxide, fluorophosphines and also by more basic phosphines to form Rh(h 5-C 9H 7)L 2 complexes. Unhindered dienes also displace ethylene from I. Several mixed ligand complexes of the type Rh(h 5-C 9H 7)LL′ (L = phosphine or CO) are also reported and possible mechanisms of ethylene displacement are discussed.

Synthesis and dynamic behaviour of bis(ethylene)(tertiary phosphine)-platinum complexes

Reactions of ethylene-saturated solutions of bis(cyclo-octa-1,5-diene)platinum in light petroleum with tertiary phosphines or triphenylarsine afford white crystalline bis(ethylene)platinum complexes [Pt(C2H4)2L][L = PMe3, PMe2, Ph, PMePh2, PPh3, P(C6H11)3 or AsPh3]. Bis(ethylene)(tricyclohexyIphosphine)platinum reacts with tetrafluoroethylene to give the mixed-olefin complex [Pt(C2H4)(C2F4){P(C6H11)3}]. These 16-electron platinum(o) complexes show dynamic behaviour in solution with rotation of the ethylene ligands. N.m.r. studies (1H and 13C) at various temperatures establish an apparent equivalence of methylene-group sites at ambient temperatures, but at low temperatures there are two CH2, group signals in agreement with a molecular structure in which the ligand atom L, the platinum atom, and the carbon atoms of the ethylene molecules are coplanar. Activation energies for ethylene rotation in the complexes [Pt(C2H4)2L] fall in the range (10.2–13.0)± 0.4 kcal mol–1, Substitution in [Pt(C2H4)2{P(C6H11)3] of C2H4 by C2F4 results in a 3 kcal mol–1 lowering of the barrier to rotation of the remaining ethylene molecule.

Steric Interactions in Organic Chemistry: Spatial Requirements of Substituents

AbstractFrom the very extensive factual material available on steric interactions in organic chemistry, the present paper reviews the investigations that provide information about the “size” (“spatial requirement”) of the substituents. After an introductory section on the results obtained with the aid of spectroscopic data and by analysis of chemical reactions, attention is turned to conformational processes, including hindered rotation in ethanes, in the biphenyl system, in butadienes, multiply substituted arenes, molecular propellers, and triptycenes. The main emphasis is placed on the explanation of sterically hindered ring inversions in bridged arenes, a class of compounds particularly suitable for the study of steric interactions. The results obtained by variation of the parameters in this system are also discussed with respect to the spatial requirements of organic substituents.

Direct determination of the rotational barrier in ethane using perturbation theory

A transition state perturbation method is derived which permits the direct determination of the energy barrier to hindered rotation in ethane as opposed to the usual subtraction of two large numbers. The method is implemented by using the coupled Hartree–Fock perturbation theory (CPHF). The value obtained for the rotational barrier of ethane through third order is 2.60 kcal/mole, while the infinite-order result gives 3.17 kcal/mole. A generalized derivation of the energy formulas in CPHF is given which provides expressions for the energy to any order. This also establishes the CPHF analog of the theorem in ordinary perturbation theory that the energy correct to order 2n+1 can be obtained from perturbed orbitals of order n.

Woodward-Hoffmann approach, the extended Hueckel method, and the barrier to rigid internal rotation in ethane

Woodward-Hoffmann approach, the extended Hueckel method, and the barrier to rigid internal rotation in ethane

Bond-function analysis of rotational barriers: Methanol

Our previous bond-function analysis of internal rotation in ethane is extended to methanol with the essential result that the dominant contribution to the barrier in these two molecules has the same origin, namely the overlap (exclusion-principle) interaction between closed-shell, localized bonds. The role of the CH3OH lone-pair orbitals is investigated. It is concluded that their main effect on the barrier is in partially shielding the oxygen nuclear charge from the bonding electrons. The amount of screening they provide is nearly independent of conformation. The potential energy functions of the staggered and eclipsed forms of methanol are studied with a double-zeta Slater basis. The calculated angles of methyl tilt are 3.4° and − 1.8°, respectively; the inclusion of tilt raises the barrier height by about 25%. The dipole moment is determined as a function of the rotational angle.

The Unrestricted Hartree-Fock Theory of Chemical Reactions. III: Instability Conditions for Paramagnetic and Spin Density Wave States and Application to Internal Rotation of Ethylene

The Unrestricted Hartree-Fock Theory of Chemical Reactions. III: Instability Conditions for Paramagnetic and Spin Density Wave States and Application to Internal Rotation of Ethylene

The Barrier to Internal Rotation in Ethane

The internal rotation barrier in ethane appears susceptible to "explanation" at a qualitative, intuitively useful, reasonably correct level. At this level, localized and delocalized MO's each produce a description. For a rigid rotation, the delocalized description is basically the "orbital control" type familiar from Woodward-Hoffmann rules (30), Walsh's rules (31), and the formation of diatomic molecules (32). This description indicates that long-range eclipsed H---H antibonding is responsible for the barrier. The equivalent localized-bond description invokes destructive interference or repulsion between eclipsed C-H bonds. The extension of this kind of description to other molecules requires care. Subsequent to rigid rotation, the relaxation of ethane into its optimum eclipsed geometry produces almost no energy change but produces an unknown degree of energy "redistribution." I have emphasized that the theoretical distinction between "orbital control" and "steric interaction" is not precise and that a clarification in terminology may be desirable in this connection. The discussion of barriers given here applies only to a limited class of molecules, exemplified by ethane. No doubt, additional factors enter into a proper description of barriers in molecules having lower symmetry or more polar bonds, or both (33). Finally, I should point out that approaches other than those in categories 1 to 3 have been made in efforts to rationalize or predict barriers to internal rotation (34). The Hellmann-Feynman theorem has been applied to find the torque on ethane at conformations between staggered and eclipsed (35). The integral Hellmann-Feynman theorem has served as a basis for discussing barriers in terms of transition densities (36) and has led to an electrostatic model for barriers which has given some remarkably successful barrier predictions (37). These approaches are mathematically valid, and it is perfectly legitimate to try to extract physical explanations from them also. Thus, several valid explanations for the barrier to internal rotation in ethane are possible. However, I feel that the explanations proposed above in terms of delocalized or localized orbitals are preferable at present inasmuch as they are couched in terms and concepts currently in the mainstream of chemical thinking.