Internal Rotation Axis Research Articles

Conformational analysis and rotational barriers for different classes of molecules in terms of many atom exchange interactions

Conformational analysis of simple molecules containing lone pair electrons such as H2O2, NH2OH, NH2NH2, is carried out as an extension of a recently proposed model where the barrier to internal rotation is assumed to arise only as a result of exchange interactions, calculated to first order using perturbation theory, among nonbonded atoms. Lone pair electrons associated to atoms located on the axis of rotation are effectively included in the model as additional nonbonded atoms. It is shown that exchange interactions among the nonbonded atoms of the extended cluster can be taken alone as responsible for the observed conformations and barriers. The model is then applied to molecules as propane and its derivatives, dimethylamine, dimethyl ether, with two consecutive axes of internal rotation and to the conformational analysis of polyoxymethylene. The results are in good agreement with experiments. The possibility of application to molecules of biological interest is discussed.

Passive motion of the elbow joint

A previously unreported method of measuring three-dimensional motion of joints, applied to two elbows obtained post mortem, showed that during flexion there is a continuous and linear change in the carrying angle, the forearm going into varus angulation as elbow flexion progresses. In addition, internal axial rotation of the forearm occurs near the beginning and external axial rotation, toward the end of flexion. With the elbow extended, the ulna shows little tendency to deviate laterally or to rotate axially during pronation and supination. The axis of rotation during elbow flexion lies approximately at the center of the trochlea.

Internal rotation in low barrier, heavy-top molecules: Calculation of energy levels

A computer program has been written for the calculation of the energy levels for internal rotation in a low barrier heavy-top molecule, such as CF3NO2. Molecules of this type are expected to exhibit microwave spectra of intermediate barrier type because the presence of a heavy internal-top increases the reduced barrier height. The necessary treatment is based on the simplest IAM of an asymmetric top molecule, i.e., where the internal rotation axis co-incides with one of the principal axes. The energy matrix can be factorized into the eigenstates of the torsion and torsion-rotation interaction Hamiltonian. This factorization greatly facilitates the calculation of high-J levels and the application of a least-squares fitting technique to observed microwave spectra. The output of the program gives the torsional eigenvalues and eigenfunctions, the rotational levels and eigenfunctions, transition frequencies together with relative intensities and first-order Stark coefficients. This program can be applied to all ranges of barrier height especially for an intermediate barrier case.

Internal rotation-quadrupole interaction in asymmetric rotor rotation spectra

A first-order theory for quadrupole hyperfine patterns is given for a semirigid model consisting of a C s frame and a C 2 v top, with a quadrupole nucleus located on the internal-rotation axis and connecting top and frame. It is assumed that the electrostatic coupling tensor is dependent on the internal-rotation angle. Typical effects are discussed for both the low- and high-barrier case.

The analysis of infrared torsional data

The calculation of barriers to internal rotation from far infrared torsional data for molecules containing a single internal rotation axis is discussed. It is suggested that, whereas a more complicated approach is necessary for the analysis of microwave data, a simplified theory, in which the torsional motion is treated as a perturbed harmonic vibration, is often sufficient for the infrared problem. The approach neglects any interaction of the torsion with overall rotation. It leads to simple expressions for the energy levels for the case in which the top has an N-fold rotational symmetry axis (i.e. the barrier has N equivalent wells). The method is extended to molecules in which both the top and framework are unsymmetrical, giving an analysis of the data in terms of a potential function of the form: ▪ The treatment is much simpler than previous treatments, and should be sufficiently accurate for much infrared data.

Effect of Internal Rotation on Angular Correlation Functions

Fluorescence polarization, nuclear magnetic resonance, and electron spin resonance experiments on appropriately labeled proteins give information about various angular correlation functions or correlation times for the reorientation of the label. Expressions are derived relating these correlation functions and times to the rotation rate of the rigid protein and the rates of the internal rotations between the label and the protein. The effective correlation time for the label is simply a series of factors times the correlation time for the rigid protein. Each internal rotation which is much faster than the protein rotation contributes a single factor ½(3 cos2θ−1)2, where θ is the angle from the internal rotation axis of interest to the next internal rotation axis, or, for the last internal rotation, to the label axis of interest. The effect of internal rotations which are much slower than the protein rotation rate is the same as the effect of averaging over molecules with a permanent geometry corresponding to the possible orientations about the internal rotation axis.

Microwave Spectra of Some Isotopically Substituted Phenols

The rotational spectra of C6H518OH, C6D5OH, and C6D5OD were successfully analyzed to obtain their respective rotational constants in the region from 20 000 to 31 000 Mc/sec. The splitting of the rotational transitions due to the hindered internal rotation of the hydroxyl group was noted in C6H518OH and C6D5OH while the spectrum of the C6D5OD isotope was unsplit. As is the case in C6H516OH, the high barrier to internal rotation produced a doublet spectrum, where the splittings were effectively independent of the J transition and correspond to 115 and 103 Mc/sec for the C6D5OH and C6H518OH isotopes, respectively. The experimental rotational constants are: IsotopeA(Mc/sec)B(Mc/sec)C(Mc/sec)C6D516OH4682.677±0.0062422.815±0.0041596.930±0.004C6D516OD4654.378±0.0052342.102±0.0041558.383±0.004C6H518OH5650.076±0.0082487.321±0.0051727.232±0.005. It was found that the structure of the C–O–H fragment could not be uniquely determined from the rotational constants. Two structures were found which were essentially the same except for C–O–H configuration relative to the internal rotation axis. Both structures fit the experimental spectra equally well and have standard deviations of 3.2 Mc/sec. The parameters for Structures (I) and (II) are, respectively: C–C, 1.3956±0.0002 and 1.3954±0.0002 Å; C–H, 1.081±0.001 and 1.082±0.001 Å; O–H, 0.985±0.01 and 0.944±0.009 Å; C–O, 1.370±0.001 and 1.379±0.001 Å; COH, 111.87±0.35 and 105.04±0.35 deg; α (off angle from rotation axis), 6.34±0.60 and −11.17±0.50 deg. In Structure (I) the oxygen and hydrogen are on the same side of the internal rotation axis while in Structure (II) they straddle it. Structure (II) is believed to be the more reasonable. Neither C–O–H structure could correlate the splitting data to one value of the barrier height, but good agreement was obtained if the moment of inertia of the hydroxyl group was based on CH3OH. The barrier height obtained was 1150 cm−1.

The Chlorine Quadrupole Resonances of Ethane Derivatives

Abstract The temperature broadening of the chlorine quadrupole resonance line-width was studied in three ethane derivatives (1, 1, 1-trichloroethane, hexachloroethane and 1, 1, 1, 2-tetrachloro-2, 2-dimethylethane) below the plastic crystalline phases. Most of the resonance frequencies observed at the temperature of liquid nitrogen were equal to those reported in the literature. The energies of activation (2.2, 2.6 and 4 kcal./mol. respectively for the three compounds mentioned above) were obtained from the line-width versus temperature curves in the low temperature phases. It was suggested, considering the smallness of the energies of activation, that the vibrational rotation of the molecule as a whole rather than the internal axial rotation may exist in those phases.

Decomposition of Chemically Activated Ethyl-d3 Radicals. Primary Intramolecular Kinetic Isotope Effect in a Nonequilibrium System

The rate of decomposition of ethyl-d3 radicals formed by chemical activation was studied at 195° and 300°K over the pressure range from 0.05 to 3.0 mm. The excited radicals decomposed by hydrogen or deuterium atom rupture or were collisionally stabilized. The rate of decomposition was determined relative to the rate of stabilization by complete product analysis. Detailed description is given. The limiting high-pressure rate for hydrogen rupture from energized ethyl-d3 radicals was determined to be 6.5×107 sec—1 at 300°K and 2.5×107 sec—1 at 195°K. The limiting low-pressure rate for hydrogen rupture was found to be 2.0×107 sec—1 at 300°K and 1.0×107 sec—1 at 195°K. The intramolecular hydrogen to deuterium rupture ratio was determined to be ∼2.0 at 300°K and ∼3.0 at 195°K for this nonequilibrium reaction system, and appreciably less than similar ratios determined earlier for the ethyl-d2 system. The disproportionation to recombination ratio for ethyl radicals was found to be 0.14 at 300°K and to be 0.17 at 195°K. The apparent isotopic H/D disproportionation ratio in ethyl-d3, measured at both temperatures, was 1.6 in reasonable agreement with the value of 1.4 of Boddy and Steacie. Theoretical rates were calculated from a quantum statistical harmonic oscillator formulation of the rate constant. Good qualitative and semiquantitative agreement has been found between the various experimental quantities of this study (as well as a previous one dealing with ethyl-d2 radicals) and magnitudes calculated from a model which has quite a loose activated complex (150 cm—1, C–C–H bends) with the figure axis rotation active, and in which the energized radical has both an active free internal rotation and figure axis rotation.

Normal Cooridinate Treatment of the Molecules with Axes of Internal Rotation (-CH2-CH2-, -CH2-CO-)

Normal Cooridinate Treatment of the Molecules with Axes of Internal Rotation (-CH2-CH2-, -CH2-CO-)

CONFIGURATIONS OF LIGANDS HAVING INTERNAL ROTATION AXES IN COÖRDINATION COMPOUNDS

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCONFIGURATIONS OF LIGANDS HAVING INTERNAL ROTATION AXES IN COÖRDINATION COMPOUNDSJ. V. Quagliano and San-ichiro MizushimaCite this: J. Am. Chem. Soc. 1953, 75, 23, 6084–6085Publication Date (Print):December 1, 1953Publication History Published online1 May 2002Published inissue 1 December 1953https://doi.org/10.1021/ja01119a547RIGHTS & PERMISSIONSArticle Views39Altmetric-Citations18LEARN 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 (290 KB) Get e-Alerts Get e-Alerts