Estimating carbon—mercury bond ionisation constants from PMR spectra of methylmercury compounds

Analysis of J(¹⁹⁹HgCH₃) spin coupling constants in PMR spectra of CH₃HgX (where X is a carbanion) shows that the affinity of various X groups for the methylmercury cation is linearly dependent on the acidity of the respective CH-acids XH.     

Force field studies of some trifluoromethyl- and trichloromethyl-mercury-II) compounds

Force constants of [Hg(CF₃)₂], [Hg(CCl₃)₂], [Hg(CF₃)X] (X = Cl, Br, or I) and [Hg(CCl₃)X] (X = Cl or Br) have been calculated using a valence force field and wavenumber data from solutions. The potential energy distributions show substantial mixing between the symmetrical stretching and umbrella deformation coordinates of the trihalomethyl groups. The high degree of mixing of HgC and HgX stretching coordinates in [Hg(CF₃)Br] and [Hg(CF₃)I] accounts for the discontinuous frequency and intensity trends in the [Hg(CF₃)X] series.The results are discussed in comparison with methylmercury and other trifluoromethyl systems.     

Metallomethanes: XIII. Vibrational spectra and force fields of cyanomercuriomethanes

Vibrational spectra with assignments and results of normal coordinate calculations for cyanomercuriomethanes CH_4−n(HgCN)_n (2 ≤ n ≤ 4) are discussed. The valence force constants of the central CHg bonds are 2.149, 1.944, and 1.798 N cm⁻¹,while those of the HgCN bonds are 2.204, 2.123, and 2.162 N cm⁻¹, for n = 2, 3 and 4, respectively. All these force constants are lower than the corresponding constants for methylmercury cyanide (2.445 and 2.379 N cm⁻¹). The overall behaviour of these force constants as a function of the degree of mercuration n is quite similar in both the cyanomercuriomethanes CH_4−n(HgCN) and methylmercuriomethanes CH_4−n(HgCH₃)_n series with the difference that there are variations in the constants at higher values in the former series. The potential energy distributions indicate that the valence vibrations of the CH, CN, and HgCN bonds are almost independent of all other vibrations, which in turn are more or less strongly coupled.     

Vibrational analysis of l-alanine and deuterated analogs

Raman spectra of the polycrystalline l-alanine analogs CH₃CH(NH⁺₃)COO^?, CH₃CH(ND⁺₃)-COO^?, CD₃CD(NH⁺₃)COO^?, and CD₃CD(ND⁺₃)COO^? have been obtained. A normal coordinate analysis is carried out based on the experimental frequencies of the four isotopic analogs and a 34 parameter valence-type force field defined in terms of local symmetry coordinates. The final refinement, in which five stretching force constants are constrained to fixed values obtained from bond length data, results in an average error of 7 cm^?1 (0.9%) for the observed frequencies of the four isotopically substituted molecules. Band assignments are given in terms of the potential energy distribution for local symmetry coordinates. For non-deuterated l-alanine, the vibrations above 1420 cm^?1 and below 950 cm^?1 may be described as localized group vibrations. By contrast, the eight modes in the middle frequency range, viz. the three skeletal stretching, the COO^? symmetric stretching, one NH⁺₃ rocking, the symmetric CH₃ deformation, and the two methyne CH deformation vibrations, are very strongly coupled to one another. Some decoupling appears to take place in the perdeutero molecule, and all but five modes can be described as localized group vibrations.     

Force constants of methylmercury(II) compounds

The results of force constant calculations of systems Hg(CH₃)X = CH₃, Cl, Br, I, CN, SCH₃ and {As(CH₃)₃}⁺) are briefly reviewed and the importance of data compatibility in comparative studies is stressed. Aspects of relationships between the force constants and other physical properties are discussed, but outside the limited series X = Cl, Br or I do not appear to be of fundamental significance.     

A joint local mode and normal mode interpretation of vibrational anharmonicity in methyl bromide

The gas-phase i.r. spectrum of CH₃Br has been studied up to 14 000 cm⁻¹. Some 32 new vibration levels are located accurately, involving up to 5 quanta (V= 5) of excitation in CH stretching. Reproduction of a total of 72 vibration levels is achieved through a joint treatment of CH stretching vibrations in a local mode basis, other vibrations in a normal mode basis, and with the inclusion of two Fermi resonances. The local mode approach satisfactorily accounts for the effects of the large Darling—Dennison vibrational interactions which occur between CH stretching modes. Fermi resonances between CH stretching and overtones of both methyl group deformation vibrations (ν₂ and ν₅) are treated explicitly. Interacting levels become quasi-degenerate at V = 3 in the case of 2ν₅, and at V = 5 in the case of 2ν₂. The analysis permits the determination of a complete set of 27 physically representative anharmonicity constants for CH₃Br, four of which are interrelated through the local mode model. Data reproduction between 600 and 14 000 cm⁻¹ is achieved with an r.m.s. error of 2.55 cm⁻¹.     

Spectra and structure of gallium compounds: Part X. Infrared and Raman spectra,vibrational assignment,and normal coordinate calculations for trimethylaminegallium trichloride

The far IR (450–480 cm^?1) and Raman (3200–3230 cm^?1) spectra of (CH₃)₃ NGaCl₃ have been recorded in the solid state and interpreted in detail on the basis of C₃ molecular symmetry. A modified valence force field model is used to calculate the frequencies and potential energy distribution of the adduct. The calculated force constants of the adduct are compared with those previously reported for the free Lewis acid and the free Lewis base moieties, and the observed differences ascribed to geometrical changes of the uncomplexed species on adduct formation and explained on the basis of the VSEPR model and non-bond interactions. Extensive coupling is observed between the GaN stretching mode and the NC₃ symmetric stretching and the NC₃ symmetric deformational modes. Strong coupling interaction is also found between the GaCl₃ antisymmetric stretch and the NC₃ antisymmetric deformation. The calculated value of 2.50 mdyn Å^?1 for the GaN stretching force constant in (CH₃)₃NGaCl₃ is larger than any of those previously determined in complexes such as (CH₃)₃NGaH₃ (2.43 mdyn Å^?1), (CH₃)₃NGa(CH₃)₃ (1.61 mdyn Å^?1), and H₃NGa(CH₃)₃ (1.08 mdyn Å^?1). The observed variations in the magnitudes of the stretching force constants of the donor—acceptor dative bond is found to be consistent with the estimated relative stabilities of this series of adducts.     

Kraftkonstanten von Verbindungen des Typs (CH3)3ElCl+X− (El = N,P, As,Sb; X− = SbCl6−)

Force Constants of Compounds of the Type (CH₃)₃ElCl⁺X^?(El = N, P, As, Sb; X^? = SbCl₆^?) For the cations (CH₃)₃NCl⁺ ( 1 ), (CH₃)₃PCl⁺ ( 2 ), (CH₃)₃AsCl⁺ ( 3 ), and (CH₃)₃SbCl⁺ ( 4 ) a normal coordinate analysis using a general valence force field is performed by the method of Fadini. The force constants are discussed. Calculations of the potential energy distribution show, that the skeletal vibrations in 4 are all characteristic vibrations, but there is a strong coupling of vibrations in 1 .     

The effect of the solvent upon the rates and machanisms of organometallic reactions: VII. A 19F NMR study of complexation of CF3 HgX (X = Cl,I, OCOCF3)

The concentration and temperature dependence of J(¹⁹⁹HgC¹⁹F) for solutions of CF₃HgX (X = Cl, I, OCOCF₃) in various solvents shows that in inert solvents these molecules exist mainly as non-solvent dimers (X = I or OCOCF₃) or as monomers (X = Cl). In strongly coordinated solvents $\text{1}\text{2}$ complexes are largely formed from CF₃HgX and the electron-donating solvent molecules. In pyridine solution an equilibrium exists between the $\text{1}\text{1}$ and $\text{1}\text{2}$ complexes. Complexes of the type CF₃HgX·D are T-shaped and have a higher relative content of s-electrons in the HgCF group compared with tetrahedral CF₃HgX·2D complexes.     

Far-i.r. spectra of charge-transfer complexes between IX (X = Cl,Br) and some pyridine and quinoline bases

Far-i.r. spectra of charge-transfer (CT) complexes of IX (X = Cl, Br) with pyridine, quinoline and their derivatives have been measured in solids. Assignments for the intermolecular NI stretching and the modified IX stretching vibrations are proposed. The force constants for these vibrations have been calculated assuming a linear triatomic model, putting a donor molecule as a point mass. The relationship between the relative decrease in the IX stretching force constants and the pK_a values of donor molecules is discussed.     

C-H stretching frequencies and C-H bond strengths of CH3X compounds

The influence of the X-group in CH₃X type molecules on the frequency of the C-H symmetrical stretching vibration has been investigated by means of normal coordinate analysis and CNDO/2 partial force constant and localized orbital calculations. The frequency of the C—H symmetrical stretching vibration was found to be dependent on the HCH angle α and the C—H symmetrical stretching force constant F_CH. By studying the partial force constants for a number of CH₃X type molecules a distinct relation between F_CH and the C—H bond length could be shown. With the help of localized orbital calculations a relation was found between the C—H bond length and the percentage ionic character of the C—H bond.     

Local modes and x,k relations in ethene and propadiene

The results recently obtained by Mills and Robiette on local-mode effects in H₂O, NH₃ and CH₄ type molecules are extended to ethene (C₂H₄) and propadiene (C₃H₄) type molecules. General relations among the anharmonic x_rs constants and the Darling-Dennison K_rrss constants for the stretching vibrations are derived, called “x,K relations”, which allow local-mode effects to be generated by adding the appropriate anharmonic and Darling-Dennison constants to the familiar normal-mode model of molecular vibrations. The general utility of x,K relations is discussed, and the results are reviewed for the molecular types for which they have so far been derived.     

Vibrational spectrum and force field of trimethyl- methoxysilane

The IR and Raman spectra of (CH₃)₃SiOCH₃, (CH₃)₃SiOCD₃, (CD₃)₃SiOCH₃ and (CD₃)₃ SiOCD₃ are presented together with results of normal coordinate calculations. Numerical values of certain force constants and effects of mechanical coupling between Si-O-C bridge vibrations and some of internal vibrations of (CH₃)₃Si and OCH₃ groups are briefly discussed.     

Metallomethanes: XII. Vibrational spectra and force fields of methylmercurimethanes

The vibrational spectra data, the assignments, and the results of normal coordinate calculations for CH_{4 − n}(HgCH₃)_n molecules (2 ⩽ n ⩽ 4) are reported. The central CHg valence force constants are 1.870, 1.653, and 1.582 N cm⁻¹ while the terminal ones are 2.121, 2,101, and 2.160 N cm⁻¹ for n = 2, 3 and 4, respectively. The latter values are 12, 21, and 27% higher than the central CHg force constants, but all of them are substantially lower than those in dimethylmercury (2.379 N cm⁻¹). These findings can be accounted for in terms of increasing shift of electron density towards the periphery of these molecules and increasing non-bonded metal-metal interaction. The nature of the normal modes is discussed.     

The vibrational spectra and normal coordinate analysis of tetracyclopropyllead

All the fundamental frequencies observed in IR and Raman spectra have been assigned to the normal modes of the molecule (C₃H₅)₄Pb (C₃H₅ = cyclopropyl). The calculated force field is compared to that of (C₃H₅)₂Hg and the Cmetal stretching force constants are discussed along with those of Me₄Pb and Me₂Hg; The similarity of the spectra of cyclopropyllead and cyclopropyl-mercury proves that the vibrations of cyclopropyl structural units are isolated in both molecules.     

Spectra and structure of gallium compounds: Part VII. Microwave,infrared and raman spectra and normal coordinate analysis of trimethylamine-trimethylgallane

The infrared (100–3500 cm^?1) and Raman (25–3200 cm^?1) spectra of the solid phases of (CH₃)₃NGa(CH₃)₃ and (CH₃)₃¹⁵NGa(CH₃)₃ have been recorded near liquid nitrogen temperatures as well as the Raman spectrum (100–3200 cm^?1) of the liquid phase at ~50°C and the low resolution microwave spectrum (26.5–39.0 GHz) of (CH₃)₃NGa(CH₃)₃. The spectra have been interpreted on the basis of C_3v molecular symmetry and a vibrational assignment is proposed for all but the torsional modes. The B value calculated from the microwave spectrum is consistent with published structural parameters reported from an electron diffraction study. A modified valence force field has been used to calculate the observed frequencies and the potential energy distribution. The force constants presented are consistent with changes in the structural parameters of the Lewis acid and base upon adduct formation. Extensive mixing has been observed among the low-frequency modes. The Ga-N stretching force constant (1.6 mdyn A^?1) has a value intermediate between those of (CH₃)₃NGaH₃ and H₃NGa(CH₃₃).The lack of apparent factor group splitting indicates that only one molecule occupies each primitive cell, situated on either a C₃ or C_3v site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

Vibrational analysis of chlorinated methylphosphonic acid and its anions

The vibrational spectra (IR and Raman) of CH₂ClPO₃H₂ and of its anions in solutions of H₂O and D₂O are reported. The IR spectra of the solid dibasic sodium and potassium salts, the solid normal and O-deuterated monobasic sodium and potassium salts and of the solid normal and O-deuterated acid are discussed. Symmetry and internal stretching force constants, stretch-stretch interactions and potential energy distributions are obtained from normal coordinate analysis of CH₂C1PO₃H₂, CH₂ClPO₃H^? and CH₂C1PO₃^2?, and the calculated and observed frequencies for O-deuterated acid and monobasic anion are compared.     

Synthesis,Raman and NMR spectroscopy of the trimetallic complexes [IrCl(SnCl3)(HgCl)(CO)(PR3)2]

Synthesis, Raman and NMR studies are presented for the new octahedral trimetallic complexes with composition [IrCl(SnCl₃)(HgCl)(CO)(PR₃)₂], R = p-XC₆H₄; X = H, CH₃O, F, Cl. Only the isomer containing the Cl₃SnIrHgCl fragment and trans phosphine ligands is observed. Force constants for the IrSn and IrHg bonds as well as ³¹P, ¹¹⁹Sn and ¹⁹⁹Hg NMR data are reported. The presence of a spin-spin coupling constant of more than 40,000 Hz between the ¹⁹⁹Hg and ¹¹⁹Sn atoms is shown to originate from a two-bond and not a one-bond interaction.     

Spectra and structure of gallium compounds: Part VI. Infrared and Raman spectra of trimethylgalliumtrimethylphosphine

The infrared (50–4000 cm^?1 ) and Raman (50–3500 cm^?1) spectra of (CH₃)₃GaP(CH₃)₃ have been recorded for the solid state at the temperature of boiling liquid nitrogen. The spectra have been interpreted on the basis of C_3v molecular symmetry and a complete vibrational assignment except for the methyl torsional modes is presented. A modified valence force field model has been utilized in calculating the frequencies and potential energy distribution. The calculated potential constants for the adducts are compared to those previously reported for the Lewis acid and the Lewis base moieties and the differences are shown to be consistent with structural changes upon adduct formation. Extensive coupling has been observed between the Ga-P stretching mode and the PtC₃ and GaC₃ deformational modes. Substantial coupling is also observed between the PC₃ and the GaC₃ rocking motions. The magnitude of the Ga-P stretching force constant is found to be much smaller (0.88 mdyn Å^?1) than that reported for (CH₃)₃PGaH₃ and the difference possibly reflects the relative stabilities of the donor-acceptor bond in the two complex species.The fact that none of the A, modes appear as doublets in the spectra, nor are any of the E modes split except for the GaC₃ antisymmetric stretch, which is believed to be due to the two isotopes of gallium, indicates that there is only one molecule per primitive cell sitting on a C_3v or C₃ site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

IR spectra of long-chain α,ω-alkanediols: 1,22-docosanediol and 1,44-tetratetracontanediol

The IR absorption spectra of α,ω-alkanediols with different chain lengths, HO(CH₂)₂₂OH and HO(CH₂)₄₄OH, in the spectral range of 400–5000 cm^?1 are analyzed. The assignment of numerous absorption bands to vibration modes in short methylene sequences and terminal hydroxyl groups is suggested. The splitting of IR absorption bands into doublets at 720–730 cm^?1 (rocking vibrations of CH₂ groups) and 1463–1473 cm^?1 (bending vibrations of CH₂ groups) testifies that the crystal unit subcells in the lamellae of alkanediols are orthorhombic with parameters typical of normal hydrocarbons. The specific features of absorption bands due to O-H stretching and C-O-H bending vibrations have been analyzed. These bands appear during formation of lengthy associates from hydrogen bonds formed by hydroxyl groups on the surface of elementary lamellae. A sharp increase in the intensity of the absorption bands in progression of C-C stretching and CH₂ wagging vibrations due to the anharmonic Fermi resonance with the stretching vibrations of C-O groups in the terminal hydroxyl groups has been detected.