Rotation Of Phenyl Group Research Articles

Synthesis of rigid, heterocyclic dipeptide analogs

The analogue that we chose to pursue can be conceptually derived from a Phe-Xaa dipeptide 1 by a series of rigidifying events (a) fixing the dihedral angle between the α and β carbons of phenylalanine; (b) blocking rotation of the side-chain phenyl group; and (c) fixing the directionality of the amide carbonyl group with respect to the indole ring and prohibiting C-N amide-bond rotation.

Carbon-13 relaxation and phenyl group rotation in a benzylidyne-capped tricobalt cluster

13C spin-lattice relaxation times of the protonated carbons in Co 3(CO) 9(μ 3-CPh) were measured as a function of temperature in the solvent chloroform. The T 1's were used to calculate the phenyl group's tumbling ( D ⊥) and spinning ( D s) rotational diffusion constants. It was observed that the ratio, D s D ⊥ > 1, revealing extremely facile internal rotation of the phenyl ring. This result is in direct contrast to earlier data on the bicapped tetracobalt cluster Co 4(CO) 10(μ 4-PPh) 2, and indicates a complete lack of steric or electronic interaction between the aromatic ring and the tricobalt nonacarbonyl skeleton. Theoretical diffusion constants calculated by the GiererWirtz Microviscosity model are in excellent agreement with experimental values of D ⊥.

Diastereoisomers with three neighbouring phenyl groups. XI—Hindered phenyl and formylmethylamino group rotations in 3‐(formylmethylamino)‐1,2,3‐triphenylpropyl chlorides

AbstractUnusually high free energies of activation for the rotation of phenyl groups, 12.1 and 11.1 kcal mol−1, are observed in the (1R*, 2S*, 3S*) and (1R*, 2R*, 3S*) isomers of 3‐(formylmethylamino)‐1,2,3‐triphenylpropyl chloride, and for the rotation of the formylmethylamino group (11.7 kcal mol−1) in the Z rotamer of the former isomer. These high barriers can be related to the interdependence of the rotation of such large planar groups in the strongly biased preferred conformations. The barriers for rotation of the formyl group are in the usual range (22.5 and 20.6 kcal mol−1) for (1R*, 2S*, 3S*) and (1R*, 2R*, 3S*) isomers, respectively.

Determination of the barrier to rotation through an orthogonal conformation (the II-barrier) in substituted styrenes by dynamic NMR spectroscopy

The barrier to phenyl group rotation in p -dimethylaminocinnamaldehyde and p -methoxycinnamaldehyde is 7.3 and 6.2 kcal mol respectively. These results are discussed in terms of the conformations of styrene and its various substituted derivatives.

Conformations of Epimers of Methyl 4,6-O-Benzylidene-2,3-di-O-Methyl-alpha-D-Glucopyranoside. An Example of Hindered Rotation of an Axial Phenyl Group as Observed by 13C Spin-Lattice Relaxation Times.

Conformations of Epimers of Methyl 4,6-O-Benzylidene-2,3-di-O-Methyl-alpha-D-Glucopyranoside. An Example of Hindered Rotation of an Axial Phenyl Group as Observed by 13C Spin-Lattice Relaxation Times.

Effect of temperature in region of γ and β relaxations on photo-oxidation of polystyrene

Atactic polystyrene films were irradiated at 254 nm in oxygen. The influence of the polystyrene mobility on chain scission and acetophenone formation in the temperature range 233–387 K has been studied. The increase of quantum yield for chain scission in the γ relaxation region was attributed to phenyl group rotation and increase of the probability of energy transfer from this chromophore to induce C-H bond scission. The considerable increase of acetophenone formation at the β relaxation was attributed to increase of oxygen interaction with the chromophore because of cooperative motion of main chain and benzene rings.

Phenyl‐group rotation in polystyrene

Journal of Polymer Science: Polymer Physics EditionVolume 23, Issue 3 p. 601-606 Note Phenyl-group rotation in polystyrene Y. Tanabe, Y. Tanabe Research Institute for Polymers and Textiles, 1-1-4 Higashi, Yatabe-machi, Tsukuba-gun, Ibaraki 305, JapanSearch for more papers by this author Y. Tanabe, Y. Tanabe Research Institute for Polymers and Textiles, 1-1-4 Higashi, Yatabe-machi, Tsukuba-gun, Ibaraki 305, JapanSearch for more papers by this author First published: March 1985 https://doi.org/10.1002/pol.1985.180230315Citations: 9AboutPDF 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 Citing Literature Volume23, Issue3March 1985Pages 601-606 RelatedInformation

Dielectric, mechanical and thermal properties of some chlorinated poly ( p-phenylene oxide)s in the solid state

The dielectric, mechanical and thermal properties were investigated for poly(2,6-dichloro-1,4-phenylene oxide) (PDCPO), poly(2-chloro-6-methyl-1,4-phenylene oxide) (PCMPO) and poly(2,6-dimethyl-1,4-phenylene oxide) (PDMPO). PDCPO exhibited two dielectric secondary relaxations designated as β and γ processes around 160 and 100K, respectively. The γ process was assigned to the motion of a trace of chloroform included in the PDCPO film. A blend film PDMPO/PCMPO ( 9 1 mixing ratio) exhibited dielectric relaxation around 330K and the process was assigned to the rotation of phenyl group with respect to oxygen-phenyl-oxygen axis. No dielectric relaxation was observed for the PDMPO film dried carefully, while the PDMPO film kept under an atmosphere of water vapour exhibited dielectric relaxation due to the motion of the water molecules at about 180K. Tensile stress at break measured on PDCPO prepared by Stamatoff's method was 38 MPa and was much higher than that for PDCPO prepared by the method reported by Blanchard et al. Temperature dependence of the dynamic Young's modulus for PDCPO measured at 110 Hz exhibited no appreciable loss peak in the range below 480K. Glass transition temperatures for PDCPO, PCMPO and PDMPO were determined to be 490, 445 and 500K, respectively, by differential scanning calorimetry.

Optical activity of lactones and lactams—I : Conformational dependence of the circular dichroism of 1,3-dioxolan-4-ones

Several optically active 1,3-dioxolan-4-ones were synthesized from corresponding α-hydroxy acids. The Cotton effect sign of these compounds can be explained by Weigang's sector rules. The existence of an equilibrium between envelope and planar conformations of the 5-membered ring was established on the basis of substituent and solvent influence on the CD. It was found that hindered rotation of phenyl group affects the CD of 5-phenyl substituted 1,3-dioxolan-4-ones.

Spin‐lattice relaxation in the rotating frame in solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide)

AbstractMethyl‐proton spin‐lattice relaxation times in the rotating frame T1ρ are reported for 10‐wt % solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide) in CDCl3. These measurements were made as a function of molecular weight and at two Larmor frequencies: 30 and 90 MHz. The T1ρs are substantially shorter than the spin‐lattice relaxation times T1, indicating conditions far from the extreme narrowing limit. However, the observed values of T1ρ correspond very well to predictions from an earlier interpretation of T1s. The interpretation was based on four motions likely in this polymer: overall rotatory diffusion, segmental motion, phenyl group rotation, and methyl group rotation. All parameters in the interpretation such as correlation times had been set in the previous interpretation of T1s, leaving none to be adjusted to account for the T1ρs. Nevertheless, agreement between the predicted and observed T1ρs is excellent; this is apparently the first such quantitative interpretation of T1ρs in a dissolved polymer far from the extreme narrowing limit. This agreement at high molecular weight points to the adequacy of the description of local motion from high frequencies to relatively low frequencies and to the improved utility of T1ρ data versus T2 data as a check of low‐frequency contributions to the spectral density. The agreement at lower molecular weights indicates that the description of long‐range motions is sufficient though clearly oversimplified by the omission of the Rouse–Zimm modes.

Dynamics of macromolecular chains. 13C spin relaxation study of short-chain polystyrenes in deutero-chloroform solution

The results of T 1, T 2 and nuclear Overhauser effect ( NOE) measurements on molecular weights 510–110 000 at weight fractions 0.05–0.60 in the title system suggest that previously neglected entanglement effects are highly significant for the reorientational processes in polymer chains and that previous T 2 estimates from bandwidths may be too low. T 2 is usually equal to T 1, and deviates only at high concentrations in these systems. The data can be represented by a double exponential reorientational correlation function of the form G(τ)= A exp( − τ τ A ) + B( − τ τ B ) where A + B = 1. The correlation times τ A and τ B are typically 1.5 × 10 −10 and 1.5 × 10 −9s, respectively. B increases with increasing concentration and molecular weight. The terminal phenyl group rotation is quite free in contrast to the backbone phenyls, and a spinning ratio above 15 has been estimated in a 60% solution for this group. Signal assignments and relaxation times ( T 1) are given for 15 different 13C signals of these polymers at high concentrations.

Conformation and Structure of Ethylbenzene in the Vapour Phase

Abstract The molecular structure of ethylbenzene has been studied by gas electron diffraction. Experi-mental intensities and radial distribution are well reproduced by an average structure with r = 70(3)°, where r is the angle between the C—C—C(H3) plane and the ring plane, mean (rg) bond lengths (C-C)phenyi = 139.9(3) pm, Cphenyi-C(H2) = 152.4(9) pm, C(H2)-C(H3) = 153.5(12) pm, C—H = 109.4(4) pm, and bond angle C-C-C(HS) = 111.8(15)°. (Estimated total errors are parenthesized.) An also acceptable perpendicular model (r = 90°) is accompanied by very large vibrational amplitudes, while the coplanar conformation (r = 0°) is excluded. Mixtures of conformers fit the experimental data as well. The barrier to rotation of the phenyl group is estimated from the average structure to be about 7 kJ mol -1 . According to CNDO/2 calculations, only the perpendicular form is stable. The results of a geometry optimization are shown.

Phenyl group rotation in polystyrene and the nature of twofold anisotropic internal rotation

AbstractA review of the experimental evidence for phenyl group rotation in various polystyrenes and improvements in the interpretation of spin relaxation data for dilute solutions of randomly coiled polymers led to a new calculation of the correlation time for phenyl group rotation from nuclear magnetic resonance (NMR) data. Both 13C and 19F NMR data were reconsidered by using a model which includes motional modulation of the dipole–dipole interaction by overall rotatory diffusion, backbone rearrangements, and internal anisotropic rotation. The choice of a twofold potential to characterize local resistance to internal phenyl group rotation strongly influences the estimate of the rate of phenyl group rotation. The magnetic resonance data are found to be consistent with a correlation time for phenyl group rotation which is one to six times longer than the average correlation time for backbone rearrangement.

Calculation of Phenyl Group Rotation in Polystyrene by Means of Semiempirical Potentials

Calculation of Phenyl Group Rotation in Polystyrene by Means of Semiempirical Potentials

Phenyl Group Rotation in Polystyrene

Phenyl Group Rotation in Polystyrene

Mechanical relaxations in a series of polyurethanes with varying hard to soft segment ratio

A series of nine polyurethanes with a systematically varying hard to soft segment ratio was prepared; their dynamic mechanical spectra were studied over a wide temperature range. These polyurethanes were prepared using Adiprene L-100 which contains polyether units (forming the soft segment material) and diphenylmethane-4,4′di-isocyanate which formed the bulk of the hard segments. The chain extender was 1,3-diaminopropane. The samples were studied at 2 per cent static strain and at a frequency of 110 Hz. They showed tan δ maxima in three temperature regions, but each sample did not necessarily show all three transitions. In general, these transitions occurred at about −130°, −20° and over a range from about 11° to over 225°. These transitions were referred to as the a, β and γ transitions in order of decreasing temperature. The transitions were interpreted in terms of molecular motion. The γ transition was thought to arise through a Schatzki type mechanism while the β transition for most samples represented the glass transition and was caused by micro-Brownian motion of the more flexible parts of the chain. The a transition, which only occurred when MDI was also present, exists in the 15–20° range for the samples with the higher soft segment concentrations; it was thought to be the result of phenyl group rotation. As the hard segment concentration was increased, spherulites were detected and the a transition shifted to considerably higher temperatures, but a shoulder remained at about 20° until hard segment concentration had reached a high level. The high temperature transition was the result of crystallite fusion.

Dynamic mechanical and dielectric relaxations of polystyrene below the glass temperature

AbstractDynamic mechanical and dielectric properties of various kinds of polystyrene, including bulk‐polymerized, monodisperse, isotactic, and thermally degraded samples, have been measured below the glass temperature to 4°K. Five relaxation processes are found, designated β, γ, γ′, δ, and ε in order of descending temperature. The β peak (350°K at 10 kHz) is attributed to the local oscillation mode of backbone chains and the γ′ peak (180°K at 10 kHz) to rotation of phenyl groups. The δ peak (100°K at 10 kHz) is observed only in dielectric properties of the bulk‐polymerized sample and is assigned to weak polar bonds, such as oxygen bonds in the chain. The δ peak (55°K at 10 kHz) which is prominent in dynamic mechanical properties is interpreted in terms of lattice defects due to a syndiotactic diad inserted between isotactic sequences in a chain or vice versa. The ε peak (ca. 25°K at 10 kHz) is first reported in the present work, but the mechanism involved is not yet clear.

The Dielectric Property of Polystyrene and Some Ring-substituted Polystyrenes in Glassy State

Measurements of dielectric properties of polystyrene and some substituted polystyrenes containing different substituents (methyl group and halogen atoms) in the phenyl ring are carried out over a temperature range from 93 to 343°K in vacuo (10-3 mmHg) at 1 and 10 kHz. The temperature dependence of dielectric loss ε'' is mardedly different according to the location of the substituent in the ring. The dielectric behavior of these polymers at temperatures around 150°K at 10 kHz is explained in terms of two modes of phenyl group motions: the hindered rotation of phenyl group around the bond to the main chain and the oscillation or wagging of phenyl rings. The relaxation observed as a shoulder at the foot of the α-loss peak in the ε''-temperature curve is attributed to the local-mode oscillation of the main chain.