Orientation Of Methyl Group Research Articles

Structure Dynamics and Isomerism of Bis[μ-(2-methylphenolato)]bis[(η2:η2-cycloocta-1,5-diene)rhodium(I)] Complex

Dinuclear rhodium(I) complex [{RhI(cod)}2(μ-OC6H4-2-Me)2] (1), exhibits the syn-anti isomerism consisting in the orientation of methyl groups of the bridge ligands with respect to the plane or distorted plane involving Rh and O atoms. The syn isomer predominates in CDCl3 solution (above 90%) at room temperature. EXSY 1H NMR measurements showed that, in CDCl3 solution, complex 1 undergoes at least two independent dynamic processes differing substantially in values of activation parameters: (i) rotation of 2-methylphenyl rings in bridge ligands along the O-C axis, and (ii) formal rotation of cod ligands along the Rh-cod axes, which proves fluxional behavior of cod ligand in RhI(cod) complexes.

Odd−Even Variations in the Wettability of n-Alkanethiolate Monolayers on Gold by Water and Hexadecane: A Molecular Dynamics Simulation Study

Molecular dynamics (MD) simulations were performed to investigate odd-even chain length dependencies in the wetting properties of self-assembled monolayers (SAMs) of n-alkanethiols [CH3(CH2)n-1SH] on gold by water and hexadecane. Experimentally, the contact angle of hexadecane on the SAMs depends on whether n is odd or even, while contact angles for water show no odd-even dependence. Our MD simulations of this system included a microscopic droplet of either 256 water molecules or 60 hexadecane molecules localized on an n-alkanethiolate SAM on gold with either an even or odd chain length. Contact angles calculated for these nanoscopic droplets were consistent with experimentally observed macroscopic trends in wettability, namely, that hexadecane is sensitive to structural differences between odd- and even-chained SAMs while water is not. Structural properties for the SAMs (including features such as chain tilt, chain twist, and terminal methyl group tilt) were calculated during the MD simulations and used to generate IR spectra of these films that compared favorably with experimental spectra. MD simulations of SAMs in contact with slabs of water and hexadecane revealed that the effects of these solvents on the structure of the SAM was restricted to the chain terminus and had no effect on the inner structure of the SAM. The density profiles for water and hexadecane on the SAMs were different in that water displayed a significant depletion in its density at the liquid/SAM interface from its bulk value, while no such depletion occurred for hexadecane. This difference in contact may explain the lack of an odd-even variation in the wetting characteristics of water on these surfaces, because the water molecules are positioned further away from the surface and, therefore, are not sensitive to the structural differences in the average orientations for the terminal methyl groups in odd- and even-chained SAMs. In contrast, the differences in the wetting properties of hexadecane on the odd- and even-chained SAMs may reflect the closer proximity of these molecules to the SAM surface and a resulting greater sensitivity to the differences in the terminal methyl group orientations in the SAMs. SAM-solvent interaction energies were calculated during the MD simulations, yielding interaction energies that differed on the even- and odd-chained surfaces by approximately 10% for hexadecane and negligibly for water, in accord with estimates using experimental wetting results.

Determination of the two methyl group orientations at vapor/acetone interface with polarization null angle method in SFG vibrational spectroscopy

We report a direct measurement of the orientation of the two CH 3 groups of acetone molecule at the vapor/acetone interface. The interfacial acetone molecule is found well-ordered, with one methyl group points away around 14.4° ± 1.9° and another into the bulk liquid around 102.8° ± 1.9° from the interface normal, and thus the C O group points into the bulk around 135.8° ± 1.9°. These results directly confirmed the highly ordered and even crystal like interfacial structure of the vapor/acetone interface from previous MD simulation. The general formulation and accurate determination of the orientational parameter D can be used to treat interfaces with complex molecular orientations.

Molecular Dynamics Simulation of Transmembrane Polypeptide Orientational Fluctuations

The orientation and motion of a model lysine-terminated transmembrane polypeptide were investigated by molecular dynamics simulation. Recent 2H NMR studies of synthetic polypeptides with deuterated alanine side chains suggest that such transmembrane polypeptides undergo fast, axially symmetric reorientation about the bilayer normal but have a preferred average azimuthal orientation about the helix axis. In this work, interactions that might contribute to this behavior were investigated in a simulated system consisting of 64 molecules of 1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) and one α-helical polypeptide with the sequence acetyl-KK-(LA) 11-KK-amide. In one simulation, initiated with the peptide oriented along the bilayer normal, the system was allowed to evolve for 8.5 ns at 1 atm of pressure and a temperature of 55°C. A second simulation was initiated with the peptide orientation chosen to match a set of experimentally observed alanine methyl deuteron quadrupole splittings and allowed to proceed for 10 ns. Simulated alanine methyl group orientations were found to be inequivalent, a result that is consistent with 2H NMR observations of specifically labeled polypeptides in POPC bilayers. Helix tilt varied substantially over the durations of both simulations. In the first simulation, the peptide tended toward an orientation about the helix axis similar to that suggested by experiment. In the second simulation, orientation about the helix axis tended to return to this value after an excursion. These results provide some insight into how interactions at the bilayer surface can constrain reorientation about the helix axis while accommodating large changes in helix tilt.

Atomistic Simulation of Orientation of Methyl Groups and Methylene Bisectors, and Surface Segregation, in Freely Standing Thin Films of Atactic Poly(ethylene-co-propylene)

Atomistically detailed models of free-standing thin films of random poly(ethylene-co-propylene) were produced using a method recently applied to atactic polystyrene (Clancy, et al. J. Phys. Chem. B 2001, 105, 11493). Monte Carlo simulations of the copolymer were carried out at ethylene fractions that cover the entire range of composition investigated in a recent experimental work (Opdahl, et al. J. Phys. Chem. B 2002, 106, 5212) based on sum-frequency generation (SFG) spectroscopy. We find that there is a minor enrichment of methyl groups on the surface, as compared to the bulk composition. Interestingly, the orientation distribution of methyl and methylene units is not unimodal. For methyl units, there is about 50% probability of orientation perpendicular to the surface. The other 50% are randomly oriented. For the methylene bisector, the simulation shows that the distribution has two broad peaks at opposite angles (at 180° apart) to the surface normal. More conclusive results may be obtained by using larger sample sizes and analysis of a larger number of snapshots, both of which increase the computation time significantly. The opposite angle pairs nearly cancel each other in the computation of an average order parameter and give us a misleading net result that the bisectors are randomly oriented. With increasing ethylene fraction, the orientation distribution of methyl and methylene units tends to become more uniform; however, this change is small. The strong average orientation of methyl groups and weak average orientation of methylene groups is in agreement with experiments. However, the simulation does not show the significant relative increase in the surface methyl groups contributing to the SFG signal as compared to the bulk concentration or an increase in average orientation of methylene units, with an increase in the ethylene fraction, as inferred from the experimental results. We find that the raw experimental data obtained with an increase in ethylene fraction can be explained by the changes in the number of methyl and methylene groups on the surface rather than the increase in surface excess of the methyl groups contributing to the SFG signal, trans cancellation, and increase in orientation of methylene bisectors as deduced from the experiments.

Anisotropic thermal expansion behavior of thin films of polymethylsilsesquioxane, a spin-on-glass dielectric for high-performance integrated circuits.

Thin films of poly(methylsilsesquioxane) (PMSSQ) are candidates for use as interdielectric layers in advanced semiconductor devices with multilayer structures. We prepared thin films of PMSSQ with thicknesses in the range 25.0-1151.0 nm by spin-casting its soluble precursor onto Si and GaAs substrates with native oxide layers and then drying and curing the films under a nitrogen atmosphere at temperatures in the range 250-400 degrees C. The out-of-plane thermal expansion coefficient alpha(perpendicular) of each film was measured over the temperature range 25-200 degrees C using spectroscopic ellipsometry and synchrotron X-ray reflectivity, while the in-plane thermal expansion coefficient alpha(parallel) of each film was determined over the temperature range 25-400 degrees C by residual stress analysis. PMSSQ films cured at higher temperatures exhibited reduced thermal expansion, which is attributed to the denser molecular packing and higher degree of cross-linking that arises at higher temperatures. Surprisingly however, all the PMSSQ films were found to exhibit very strong anisotropic thermal expansion; alpha(perpendicular) and alpha(parallel) of the films were in the ranges 140-329 ppm/ degrees C and 12-29 ppm/ degrees C respectively, depending on the curing temperature. This is the first time that cured PMSSQ thin films have been shown to exhibit anisotropic thermal expansion behavior. This anisotropic thermal expansion of the PMSSQ thin films might be due to the anisotropy of cross-link density in the films, which arises because of a combination of factors: the preferential orientation of methyl groups toward the upper film surface and the preferential network formation in the film plane that occurs during curing of the confined film. In addition, the film electron densities were determined using synchrotron X-ray reflectivity measurements and the film biaxial moduli were obtained using residual stress analysis.

Molecular conformation effects on mesomorphism and twisting ability of chiral cyclohexanones in mesophases

The molecular conformations of 2,6-bis-(4-phenyl)benzylidene-3R-methyl-cyclohexanone and its mono-(4-phenyl)benzylidene methylcyclohexanone isomers were investigated by molecular simulation using the semiempirical AM1 and PM3 methods and by analyzing the experimental spin-spin coupling constants in the PMR spectra. Mesomorphism and the twisting ability of the induced cholesteric mesophases of the title compounds are analyzed using the ratios between conformers with the axial and equatorial methyl groups and other peculiarities of the spatial structure of molecules (differences in anisometricity and in the degree of flattening of the cinnamoyl fragment). The equatorial orientation of the methyl group in the dominant conformations generally favors the formation of mesophases. The twisting ability is higher for chiral compounds with an axial methyl substituent and with the chiral center directly bonded to the enone and arylidene groups.

X-Ray and neutron powder diffraction studies of the crystal structure of vitamin K3Electronic supplementary information (ESI) available: X-ray powder diffraction data. See http://www.rsc.org/suppdata/nj/b3/b306072a/

The previously unknown structure of vitamin K3 (menadione, 2-methyl-1,4-naphthoquinone, C11H8O2), a synthetic compound from which it is possible to derive the naturally occurring K vitamins, has been solved from X-ray powder diffraction data. Solution was achieved using simulated annealing and restrained Rietveld refinement, using restraints derived from similar known structures. Further refinement has been carried out using neutron diffraction data; this confirmed the molecular packing and allowed further insight into the structural detail with regard to methyl group orientation, thus allowing the proposal of an extensive C–H⋯O hydrogen bonding scheme by reference to comparable known structures. The crystal structure consists of chains of molecules lying head-to-tail. This study may aid the understanding of the biological activity of vitamin K.

Detecting Molecular-Level Chemical Structure and Group Orientation of Amphiphilic PEO−PPO−PEO Copolymers at Solution/Air and Solid/Solution Interfaces by SFG Vibrational Spectroscopy

The molecular chemical structure and group orientation of a series of pluronic copolymers at both solution/air and solid/solution interfaces have been investigated using sum frequency generation (SFG) vibrational spectroscopy. Both solution/air and solid/solution interfaces are dominated by hydrophobic PPO blocks. The methyl groups on PPO blocks orient at the interface differently, depending on the solution concentration or the solid contacting media. For the saturated solution/air interface, the methyl groups on PPO blocks tend to orient preferentially along the interface normal and show a relatively ordered structure. However, at very low concentrations, pronounced changes in methyl group orientation have been observed, which explains the low-concentration break on the surface tension data vs log concentration curve. The solid/solution interface is also dominated by PPO blocks, and the orientation of the methyl groups on PPO blocks varies with different solid contacting media. Different conformations of copolymers at different solid/solution interfaces can be related to interfacial molecular interactions. The favorable interactions between hydrophobic surfaces and hydrophobic methyl groups on PPO blocks cause more ordered structures, with these groups preferentially oriented along the interface normal. The interactions between less hydrophobic surfaces and hydrophobic methyl groups are not very favorable, causing a less ordered methyl group arrangement at the interface. We have demonstrated that SFG is an appropriate technique to obtain a molecular-level picture of pluronics at different interfaces.

ゴムの電気特性，最近の進歩 ポリマー碍子における発水性と複合劣化現象

Advantages of polymer insulators over traditional ceramics insulators are light weight, high mechanical strength to weight ratio and high vandal damage resistance. Easy handling, easy installation and the thereby reduced cost are expected to contribute to more effective and labor-saving power delivery systems. The induced aging can reduce the electrical performances as well as the durability of polymer insulators. This is a peculiar nature of polymer insulators. Nowadays, silicone rubbers incorporated with alumina trihydrate (Al2O3•3H2O) filler are representative housing materials of polymer insulators. One merit of using silicone rubbers is providing stable hydrophobicity, which can be quickly recovered even when it is lost as a result of discharges and/or deposits of contaminations, to insulator surfaces. Stable and recoverable hydrophobicity prevents water film to form, restricting leakage current passing through the water film and thus enhancing the capability of electrical insulators even in wet and contaminated conditions. Fundamental understanding is reviewed on the loss and the recovery of hydrophobicity of silicone rubbers in association with a formation of low molar mass cyclic silicone oligomers, a formation of silanol groups and an orientation of methyl groups. A correlation of the hydrophobic variation with the electrical insulating performances is also reviewed.

Sum Frequency Generation Vibrational Spectroscopy Studies on “Buried” Polymer/Polymer Interfaces

Sum frequency generation (SFG) vibrational spectroscopy has been successfully applied to study “buried” poly(n-butyl methacrylate) (PBMA)/polystyrene (PS) or deuterated PS (d-PS) interfaces in situ. Orientation information on ester side chain methyl groups of PBMA at these interfaces has been deduced from the SFG spectra and compared to those of PBMA/air and PBMA/water interfaces. Our results indicate that the ester side chain methyl groups have different orientation at different interfaces. These methyl groups tend to stand up on the PBMA surface in air and tend to lie down on the surface upon contacting water. At the PBMA/PS (d-PS) interface, the orientation of ester side chain methyl groups is between the two extremes of the PBMA/air and PBMA/water interfaces. To further prove that the orientation change of methyl groups at the PBMA/PS interface is due to the interaction effect with PS, the “buried” interface between PBMA and a thin layer of polymer with phenyl groups on water has also been investigated.

Triangulo-Hg3(µ-dppm)3](O3SCF3)4: first complete NMR analysis of a homoleptic [M3(µ-dppm)3] type system and study of the conformation dynamics in solution by use of its dpam/mdppm derivatives

The 31P and 199Hg spectra of the new subvalent [triangulo-Hg3]4+ based clusters [Hg3(μ-mdppm)3](O3SCF3)4 (1a; mdppm = Ph2PCH(Me)PPh2), which is formed stereoselectively with a syn–anti–anti orientation of the methyl groups, and [Hg3(μ-dppa)3](O3SCF3)4 (4; dppa = Ph2PNHPPh2) are successfully simulated with the program WIN-DAISY. By use of the parameters derived from 1a and 4 the spectra of the parent system [Hg3(μ-dppm)3](O3SCF3)4, which show a very complex pattern, are for the first time completely analysed. The simplification of the spectral pattern in 1a or 4 compared to [Hg3(μ-dppm)3](O3SCF3)4, respectively, is a result of either symmetry reduction (1a) or quasi selective variation of one Hg–P coupling constant (4). For δ(31P), δ(199Hg), J(HgHg) and the different classes of P–P and Hg–P couplings specific values are found, some of which are powerful tools for the identification of [triangulo-Hg3]4+ compounds. The 1H NMR parameters of 1a, anti- and syn-[Hg3(μ-dpam)(μ-mdppm)2](O3SCF3)4 (2a, 2b; dpam = Ph2AsCH2AsPh2), [Hg3(μ-dpam)2(μ-mdppm)](O3SCF3)4 (3) and [Hg3(μ-dpam)3](O3SCF3)4 lead to a rational interpretation of conformation dynamics in these systems: The three five-membered rings formed by the edges of the [triangulo-Hg3]4+ cluster and the three bridging ligands adopt C-envelope conformations in a way that two of the flaps are oriented above and one below the Hg3 plane, and vice versa. The mdppm ligands feature a rigid conformation with an equatorial methyl group and an axial hydrogen atom at the flap carbon atom. The methylene carbon atom of the dpam ligands is able to flip between two positions above and below the Hg3 plane, if the relative orientations of the three flaps mentioned above are retained. The overall found rigid conformation of the bridging mdppm ligand allows a qualitative estimation of relative thermodynamic preferences of isomers resulting from syn or anti orientation of mdppm methyl groups.

Nodulisporic acid A synthetic studies. 2. Construction of an eastern hemisphere subtarget.

In this, the second of two Letters, we describe an effective assembly of (+)-4, an eastern hemisphere subtarget comprising the FGH rings of (+)-nodulisporic acid A (1) (17 steps, 9% overall yield). Central to the synthesis is a Koga three-component conjugate addition-alkylation sequence which secures the trans orientation of the vicinal quaternary methyl groups. [reaction: see text]

Theoretical Studies of Solid Nitromethane

A classical potential to simulate the dynamics of a nitromethane crystal as a function of temperature and pressure is described. The intramolecular part of the potential was taken as superposition of bond stretching, bond bending, and torsional angles terms. These terms were parametrized on the basis of the geometric and spectroscopic (vibrational frequencies and eigenvectors) data obtained using ab initio molecular orbital calculations performed at the B3LYP/6-31G* level on an isolated molecule. The intermolecular potential used is of the Buckingham 6-exp form plus charge−charge Coulombic interactions and has been previously developed by us (Sorescu, D. C.; Rice, B. M.; Thompson, D. L. J. Phys. Chem. 1997, B101, 798) to simulate crystals containing nitramine molecules and several other classes of nitro compounds. The analyses performed using constant pressure and temperature molecular dynamics simulations and molecular packing calculations indicate that the proposed potential model is able to reproduce accurately the changes of the structural crystallographic parameters as functions of temperature or pressure for the entire range of values investigated. In addition, the calculated bulk modulus of nitromethane was found in excellent agreement with the corresponding experimental results. Moreover, it was determined that the present potential predicts correctly an experimentally observed 45° change in methyl group orientation in the high-pressure regime relative to the low-temperature configuration. The analysis of the linear expansion coefficients and linear compression data indicate anisotropic behavior for the unit cell edges.

Fabrication of Noncovalent and Covalent Internal Scaffolding in Monolayer Assemblies Using Diacetylenes

Internal molecular scaffolding is created by the lateral association of molecules at specific vertical positions within a single molecular layer. In this paper, such internal scaffolding is demonstrated for both noncovalent and covalent interactions using diacetylene-containing precursors. Previously shown to form a covalent polymer backbone upon UV irradiation, diacetylenes are shown here to also exhibit noncovalent lateral interaction prior to polymerization. Preferential twist orientation of the methylene side chains and distinct methyl group orientation illustrate the presence of this noncovalent scaffolding. Upon formation of the cross-linked polymer backbone, alkyl chain crystallinity and end group orientation are not significantly altered, but the methylene chain twist orientation is decreased. Evaluated as a function of the vertical position of the scaffolding within the monolayer, all monolayers exhibit excellent long-range order as measured by the electron-transfer properties.

Density Functional Studies on N-Methylacetamide−Water Complexes

Density functional theory (DFT) calculations were performed to study the conformations, hydrogen-bonding effects, and the stabilities of different methyl group orientations of isolated trans- and cis-N-methylacetamide (NMA) and of 12 NMA−water complexes. The DFT functionals B3LYP, BLYP, and the basis set 6-311++G(d,p) were used all through the calculations. The isolated trans-NMA structures obtained from these two DFT methods are consistent with experimental data from gas-phase electron diffraction and comparable to MP2 calculations at a much lower cost. Cooperative effects of hydrogen bonding were found in the trans-NMA·2H2O complexes, in which the two water molecules attach to the NH and CO groups of trans-NMA, respectively. No substantial H-bonding cooperative effect was found for cis-NMA−water complexes. The trans-NMA structures with the methyl orientations Φ = Ψ = 0° and Φ = 180° and Ψ = 0° are the most stable conformations of isolated trans-NMA, and the structure with Φ = 180° and Ψ = 0° corresponds...

Spontaneous Orientation of Alkyl and Alkoxy Cyanobiphenyl Liquid Crystals on the Metallic Substrate

Abstract Infrared reflection absorption spectroscopy (IR-RAS) was applied to analyze the spontaneous orientation behavior of alkyl and alkoxy cyanobiphenyl liquid crystals on the metallic substrate. The long axis of the liquid crystal molecules was shown to orient perpendicular to the substrate plane. The orientation function was evaluated from the relative intensity of the CN stretching vibration and the out-of-plane deformation of the biphenyl ring. The temperature dependence of orientation functions was studied using a heating and cooling apparatus. The orientation functions gradually decreased with the rise in temperature in the liquid crystal phase and fell off to the range of 0.1-0.2 above liquid crystal - isotropic transition. The orientation function of the terminal methyl group was evaluated from the relative intensity of the symmetric and asymmetric stretching vibrations of the methyl group. The orientation of the methyl group was discussed in relation to the conformation of the methylene sequence.

SFG study of two-dimensional orientation of surface methyl groups on cadmium arachidate Langmuir-Blodgett films

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSFG study of two-dimensional orientation of surface methyl groups on cadmium arachidate Langmuir-Blodgett filmsNaotoshi Akamatsu, Kazunari Domen, and Chiaki HiroseCite this: J. Phys. Chem. 1993, 97, 39, 10070–10075Publication Date (Print):September 1, 1993Publication History Published online1 May 2002Published inissue 1 September 1993https://doi.org/10.1021/j100141a029RIGHTS & PERMISSIONSArticle Views542Altmetric-Citations65LEARN 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 (754 KB) Get e-Alerts

Effect of Methyl Substitution on Conformation and Molecular Arrangement of BEDT-TTF Derivatives in the Crystalline Environment

Abstract Two methylated bis(ethylenedithio)tetrathiafulvalene (ET) derivatives, Me2ET and Me4ET were stereoselectively synthesized to examine the effect of methylation on conformations of dihydrodithiin rings and molecular arrangements in the crystalline state. Since the donating ability of Me2ET and Me4ET are similar to that of ET, the methylated ET derivatives are considered to be appropriate to investigate the “lattice pressure” effect on ET radical salts by changing the volume of donor molecules. The upper limit of an activation energy for the ring inversion of the dimethylated dihydrodithiin in solution was estimated to be 32 kJ mol−1 by 13C NMR spectroscopy. The X-ray structure analyses revealed that orientations of methyl groups are fixed to axial in Me2ET and to equatorial in Me4ET, accompanied by the change of molecular stacking. The “volume of a methyl group” was evaluated by comparing the molecular volumes of Me2ET and Me4ET with that of ET, and the effective volume for the axial methyl group turns out to be 15% larger than that of the equatorial. The solid state 13C NMR (CP/MAS) spectra of ET and its derivatives showed that the chemical shifts of resonance lines reflect the conformations of dihydrodithiin rings in crystals.

Phase transitions in the dimethyl thallium(III) halides, (CH3)2TIX(X = Cl, Br, I)

Abstract The dimethyl thallium(III) halides were investigated at low temperature and at high pressure by IR and Raman spectroscopy. These compounds have a tetragonal structure under ambient conditions, in which the methyl groups are disordered. Ordering transitions were observed at low temperature in all three halides. The low-temperature unit cells are monoclinic or triclinic with C2h or Ci symmetry and Z = 1 and Z = 2 per primitive unit cell for the chloride and for the bromide and iodide, respectively. At high pressure, the iodide and bromide underwent phase transitions at just below 10 kbar to phases similar to those observed at low-temperature. A second transition was observed in both the iodide and bromide at 27 and 45 kbar, respectively, which involved a change in conformation of the (CH3)2Tl+ ion from linear to bent and a distortion of the (TlX)nlayers. Significant spectral changes were also observed for the iodide and bromide at close to 65 kbar and 70 kbar, respectively, indicating the presence of another transition involving a change in methyl group orientation. The chloride underwent a transition at about 15 kbar at which the methyl groups become ordered. This phase appears to be related to that observed at low-temperature for the bromide and iodide. Further changes were observed at just below 25 kbar indicating that the (CH3)2Tl+ ions become bent. There is evidence for another transition above 35 kbar from changes in slope on plots of ν versus p.