Showing papers in "Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy in 1964"

The infra-red spectra of layer silicates

Abstract: The infra-red absorption bands arising from the structural hydroxyl groups of a number of dioctahedral and trioctahedral layer silicates are reported with grating resolution in the 3750–3500 cm−1 region. The frequency differences and orientation behaviour of these bands are discussed in terms of the known structures of the minerals. The effect of the deviation from hexagonal symmetry shown by the tetrahedral layers of dioctahedral minerals on their vibrations is theoretically analyzed, and shown to account for some of the principal differences between the spectra of dioctahedral and trioctahedral layer silicates in the 1300 to 400 cm−1 region. Comparison of the spectra of random and oriented specimens of dioctahedral layer silicates in this region permits an assignment of some of the principal absorption bands to particular vibrational modes of the crystal lattice, and reveals some surprising differences between corresponding vibrational frequencies in related structures. Effects on the spectra of Al-for-Si substitution in the lattice of both dioctahedral and trioctahedral minerals are reported. A striking effect of particle size on the appearance and position of some of the stronger absorption bands of the kaolin minerals is related to the direction of the dipole moment change associated with these vibrations. Minerals examined include pyrophyllite, beidellite, rectorite, muscovite, margarite, montmorillonite, nontronite, celadonite, lepidolite and kaolins in the dioctahedral series, and talc, hectorite, saponite, phlogopite and biotite in the trioctahedral series.

Infrared absorption study of metal oxides in the low frequency region (700-240 cm−1)

Abstract: The characteristic frequencies of oxides of 52 metals have been studied in the region 700-240 cm−1. Data for oxides of metals of different valence states and the frequencies of polymorphic forms of several oxides are presented. A particle size of 10 μ or smaller was found to give the best representative spectrum.

Infrared absorption spectra of aquo complexes and the nature of co-ordination bonds

Abstract: The infrared spectra of aquo complexes, MSiF 6 .6H 2 O (M = Ni, Mn and Fe), NiCl 2 .6H 2 O, MnCl 2 .4H 2 O, MSO 4 .7H 2 O (M = Zn and Mg), CuSO 4 .5H 2 O and CrCl 3 .6H 2 O, and some of their deuterium compounds have been reported for the frequency range from 4000 to 270 cm −1 . In addition to the OH stretching and OH 2 scissors frequencies of the co-ordinated water, there have been observed two or three absorption bands in the low-frequency range 1000-270 cm −1 . The band of weak intensity observed in the range 900-600 cm −1 and that of medium intensity observed in the range 650-450 cm −1 have been assigned to the OH 2 rocking and wagging modes, respectively, because of the isotopic shift of their frequencies. The broad band observed in the range 500-300 cm −1 has been assigned to the metal—oxygen stretching vibration. A normal co-ordinate treatment has been made for one complex ion of T h symmetry and for D 4 h symmetry on the basis of Urey—Bradley type potential and the bond stretching force constants for the various metal—oxygen bonds have been calculated. The values for the force constants vary in the order Cr(III) > Ni(II) > Mn(II) ≈ Fe(II) > Cu(II) ≈ Zn(II) > Mg(II), showing that the degree of covalent character of the metal—oxygen bonds decreases in the same order. The largest value of bond stretching force constants K(CrO) is 1·3 md/A, which is still smaller than those for the metal—nitrogen bonds of amine and nitro complexes and those for the metal-carbon bonds of cyanide complexes.

Nuclear magnetic resonance study of some α-amino acids—II. Rotational isomerism

Abstract: It is shown that the average coupling constant [Jav = 1 3 (Jt + 2Jg)] for the system CCH2CH(NH2)CO2− derived from different measurements and calculated from data reported in literature does not change appreciably although the molecules containing the above fragment are chemically quite different. The parameters derived are used to calculate relative residence times and free energy differences for the rotational isomers of some α-amino acids in alkaline solution. The accuracy of determination5 of this kind is discussed.

Spectra of phosphorus compounds—I the infra-red spectra of orthophosphates

Abstract: Infra-red spectra of PO3−4, HPO2−4, H2PO−4 ions, phosphoric acid, and their deuterated analogues, in aqueous solution and in a number of crystalline salts, are reported. The spectra, together with published Raman data, are assigned on the basis of changes in symmetry through the series PO3−4 (Td), HPO2−4 (pseudo—C3v), H2PO−4 (C2v, or lower), H3PO4 (lower than pseudo-C3v). The origin of subsidiary or double OH stretching bands is discussed. Bands in the region of 2300–2400 cm−1 (1750–1850 in deuterated compounds) are attributed to proton-tunnelling effects; bands in the 1600–1850 cm−1 region probably arise from combination tones. The POH in-plane deformation mode absorbs in the region of 1250 cm−1.

The calculation of force constants and normal coordinates—IV XH4 and XH3 molecules

Abstract: Normal coordinate calculations of XH 4 and XH 3 molecules are reviewed and discussed. It is shown that for most of these molecules the true values of the force constants in the most General Harmonic Force Field can be uniquely determined only by making use of vibration-rotation interaction constants. It is emphasized that without these extra data the GFF is not determined. The results are compared with various model force fields for these molecules.

Characteristic infrared absorption frequencies of organophosphorus compounds—I The phosphoryl (PO) group

Abstract: The frequency limits, between which the phosphoryl valence vibration is found, are tabulated for over 900 organophosphorus compounds distributed between 69 general types of structure. These correlations are further broken down to cover more detailed structures, in those cases for which the evidence shows the frequency to vary significantly with changes in the structure. The dependence of the phosphoryl frequency upon the inductive effects of substituent groups attached to the phosphorus atom is also discussed. A modified linear relationship between the phosphoryl frequency and the sum of the ‘phosphorus inductive (II) constants’ is proposed together with new and revised values for such constants. The accuracy of the relationship is shown to be better than ± 12 cm −1 for most of the compounds considered. The partial failure of the relationship for some classes of organophosphorus compounds is discussed in terms of possible perturbing factors such as hydrogen bonding, resonance, tautomerism and field effects.

The infra-red spectra of chloro- and bromobenzene derivatives—II. Nitrobenzenes

Abstract: This paper is the second in a series to assign CX stretching and deformational modes in halogeno-benzenes. The assignment of these CCl and CBr modes are easily achieved by comparison of the chloro and bromo-compounds. The CN stretching frequencies of the halogeno-nitrobenzenes have been assigned in the region 1280–1240 cm−1, and these frequencies have been chosen by comparison of known CN stretching frequencies of other nitrogen compounds with the known CN bond lengths. The low frequency band at about 800 cm−1, previously assigned to the CN stretch, is now shown to be the NO2 in-plane deformation. The modification of the substitution pattern in the o-, m- and p- isomers due to the presence of a deactivating group has been considered. In the o-isomers the band at 775 cm−1 has been considered as indicative of electronic interaction between the two ortho groups.

Characteristic infrared absorption frequencies of organophosphorus compounds—II. PO(X) bonds

Abstract: The characteristic infrared absorption frequencies associated with POH, POP and POC bonds are discussed. It is shown that the observed frequencies can be correlated with the overall chemical structure of the molecule, although not to the same extent as with the phosphoryl (PO) bond. In the case of the PO stretching vibration of the PO(H) bond, a linear relationship, between the vibration frequency and the sum of the phosphorus inductive (π) constants of the substituents attached to the phosphorus atom, is derived.

The calculation of force constants and normal coordinates—V constrained force fields for a series of methyl and dimethyl compounds of 3-fold symmetry

Abstract: Using a general refinement programme developed for use with an electronic computer, force constants and normal coordinates have been determined for the series of molecules: methyl acetylene, methyl cyanide, methyl isocyanide, 1-chloro-, 1-bromo-, 1-iodo-propyne, dimethyl acetylene and ethane. In each case a method of successive refinements was used to obtain the best set of force constants consistent with all the available data on vibration frequencies, Coriolis zeta constants and centrifugal stretching constants for all possible isotopes. The experimental data were weighted according to their estimated reliability, and the standard errors of the force constants have been calculated in the last cycle of refinement. Constrained force fields have had to be used in order to obtain well-conditioned sets of force constants; all force constants insensitive to the data used have been constrained to equal zero. The final sets of force constants, which form a remarkably consistent group, are discussed briefly and compared with previous estimates for the same molecules. A force field of general applicability for the CHC group is postulated in Tables 19 and 20.

2,2'-dipyridyl complexes of rare earths. i. preparation, infra-red and some other spectroscopic data

Abstract: Complexes of rare earths with 2,2′-dipyridyl of the type [M(Dip)2(H2O)n]+3 X3 (where M+3 = Pr, Sm, Eu, Gd, Tb, Dy and Er; Dip = dipyridyl, x = Cl− or No3− and n = no of water molecules) are described. Infra-red studies with probable assignments are presented. The dipyridyl band at 990 cm−1 is shifted to higher frequency (∼1010 cm−1) in the chelates indicating the formation of a complex. Two new peaks between 1480–1500 cm−1 are observed in the spectra of all chelates. Preliminary observations on the fluorescence properties of the chelates are included. Sm(III) and Dy(III) chelates showed weak fluorescence. The characteristic line emission is present in Eu(III) and Tb(III) chelates. The fluorescence of the Gd(III) complex is due to the presence of minute Eu(III) and Tb(III) impurities, and the energy transfer from dipyridyl molecules bound to Gd(III) is quite effective.

A comparison of Urey Bradley and valence force-fields for chlorinated benzenes

Abstract: Urey-Bradley and valence force-constants are obtained from a least-squares refinement of ∼344 planar vibrational frequencies of a series of chlorinated benzenes. The valence force-field was found to give a significantly better frequency fit with 26 adjustable parameters than the Urey Bradley force-field which contained 38 adjustable parameters. Comparisons are made between the force field constants of the two models.

Valence force calculation of the vibrational spectra of crystalline isotactic polypropylene and some deuterated polypropylenes

Abstract: The vibrational frequencies of crystalline isotactic polypropylene, poly(333d3-propylene), poly(11d2-propylene), poly(2d1-propylene), and poly(d6-propylene) have been calculated using valence force constants derived from saturated hydrocarbons. Good agreement with the observed frequencies is found. Normal coordinates and potential energy distributions have been determined.

Vibrational assignments for glyoxal, acrolein and butadiene

Abstract: The infrared spectra of glyoxal, acrolein and butadiene have been re-examined and the range of observation has been extended down to 100 cm−1. Low frequency fundamentals have been found for the first time for all three molecules, and a complete vibrational assignment has been made for acrolein. Approximate frequencies for the Raman-active modes of glyoxal have been deduced from infrared-active combination bands, and the vibrational assignments for glyoxal and butadiene have been revised.

The fundamental vibrational spectra of the formates of the main group elements

Abstract: The infra-red spectra of twenty formates have been measured as mulls in Nujol and hexachlorobutadiene. The influence of the metal ion on the carboxylate stretching frequencies has been investigated, and possible correlations between spectra and structure considered.

The infrared spectrum of carbon suboxide

Abstract: The infrared spectrum of gaseous and solid C 3 O 2 has been examined from 70 to 4000 cm −1 . Because impurity bands have been a problem in the past, strenuous efforts were made to obtain an authentic spectrum. Samples were prepared by three different methods. (1) by dehydration of malonic acid with P 2 O 5 , (2) by dehydration of malonic acid-d 4 with P 2 O 5 , and (3) by pyrolysis of diacetyl tartaric anhydride. All three gave samples whose infrared spectra were quantitatively identical. In addition only traces of impurities were found by gas chromatography. The spectrum reported here is therefore surely that of pure C 3 O 2 . The range 70–400 cm −1 was examined with very thick gas and solid samples in an effort to locate the lowest fundamental. It was not observed, and is surely outside this region. The spectrum of the gas from 400 to 4000 cm −1 was examined with a resolution of 0·5–1 cm −1 . Six of the seven fundamentals for the linear form are known with certainty, and the seventh is believed to be below 70 cm −1 . Nonetheless there are many features of the spectrum which are still unexplained, and the analysis is far from satisfactory.

The calculation of force constants and normal coordinates—VI. Force constants of the silyl group

Abstract: Normal coordinate calculations have been carried out for a number of molecules of three-fold symmetry containing the silyl group. All available data on frequencies and Coriolis interaction constants for all isotopic species (where possible) were used in force constant refinement calculations. Since these data were not sufficient to fix the general harmonic force field (GFF), the silyl group force field was constrained according to the model which has been successfully applied to the methyl group in previous papers in this series. In general, the refinements were made independently for each molecule, and the results show a pleasing degree of uniformity for the silyl group when the nature of the fourth atom attached to the Si atom is taken into account. On the basis of the transferability of force constants in almost identical molecules, some assignments for silyl acetylene and methyl silyl acetylene are questioned, and alternative assignments proposed.

Infrared spectra of normal higher alcohols—I

Abstract: A The infrared spectra of the solid normal primary alcohols C12H25OH through C37H75OH (except C36H73OH) have been measured. The correlation between the crystal forms and the spectra has been studied. The band progressions have been analysed and compared with those of n-paraffins.

Characteristic infra-red absorption frequencies of organophosphorus compounds—III. Phosphorus-sulphur and phosphorus-selenium bonds

Abstract: The characteristic infra-red absorption frequencies of the PS, PS(C), PS(P), PS(H) and PSe bonds are tabulated as a function of the overall chemical structure of the molecule. The PSe(X) absorption bands are found to fall outside the region (2–25 μ) for which data are available. Both the PS and the PSe bonds are found to be characterised by two absorption bands and possible reasons for this are discussed. The dependence of the characteristic absorption frequencies on molecular environment is demonstrated and this is found to be less dependent on the inductive effects of substituents than was the case for bonds between phosphorus and oxygen.

Infrared spectra of some hexahalogeno complexes

Abstract: Infrared spectra of hexachloro complexes have been measured from 14 to 35 μ A strong band observed in the range 350 ∼ 300 cm −1 was assigned to the triply degenerate stretching vibration, ν 3 A normal co-ordinate treatment has been made for these complex ions on the basis of the molecular force field adequate for some hexafluorides The nature of metal-halogen co-ordination bonds has been discussed on considering the bond stretching force constants obtained The result is in agreement with that of the pure quadrupole resonance study of halogens

Characteristic group frequencies of bromo and iodoalkanes in the cesium bromide region

Abstract: The infrared spectra of 74 normal and branched bromo and iodoalkanes have been recorded and studied in the range of 667-286 cm−1. It was found that the number and position of the frequencies characteristic of the CX stretching vibration are dependent on the rotational isomers present as well as the structure of the alkyl substituents in the vicintiy of the CX group. Conformational structures and representative spectra are presented along with correlation charts which list the CX stretching vibration for various primary, secondary and tertiary bromo and iodoalkanes.

Vapour and crystal spectra in polarized light of pyrazine-d0, cis pyrazine-d2 and pyrazine-d4

Abstract: The infrared spectra of pyrazine-d0, cis pyrazine-d2 and pyrazine-d4 have been measured between 4000 and 400 cm−1. The spectra have been obtained in the vapour and solid states. The dichroic behaviour of the bands has been measured on polycrystalline fully oriented samples. The vibrational assignment of the three isotopic species id discussed on the basis of the rotational band envelopes, of the polarization measurements and of the product rule. All infrared active modes are assigned and from the infrared spectrum of cis pyrazine-d2 evidence is obtained for the choice of infrared inactive modes of pyrazine.

Vibrational spectra of fumaronitrile, maleonitrile and tetracyanoethylene

Abstract: Infrared and Raman spectra are reported for fumaronitrile, maleonitrile, and tetracyanoethylene. The infrared observations extend from 4000 to at least 100 cm−1. The Raman data include polarizations, although they are incomplete for tetracyanoethylene. The data and assignment for fumaronitrile agree very well with the recent results of Devlin , Overend and Crawford . Two fundamentals which they inferred have been confirmed by direct observation. All fundamentals are now known except for two au modes. Values are given for all but one of the fundamentals of maleonitrile. For tetracyanoethylene the assignment of the planar vibrations has been aided by comparison with frequencies calculated from Urey-Bradley force constants. The latter were obtained from an overlay treatment of three other cyanoethylenes. The assignments for the out-of-plane fundamentals are still unsatisfactory.

Infrared absorption spectra of inorganic solids—III Selenates and selenites

Abstract: The infrared absorption spectra of four selenates and five selenites are presented for the region 400–4000 cm −1 . Spectral information below 400 cm −1 was obtained, using CsBr optics, and is also tabulated. The infrared-active, characteristic vibrational modes for the SeO 4 = ion in solid inorganic selenates fall in the regions ∼420 cm −1 (bending) and ∼895 cm −1 (stretching) whereas for solid inorganic selenites they are at ∼460 cm −1 and ∼740 cm −1 , respectively. In crystalline environments the bands often show considerable splitting. Hydrated selenites and selenates have complicated spectra probably due to the formation of selenic or selenious acids, and hydrogen-bonded structures. The thermal decomposition of calcium and cadmium selenates to selenites has been qualitatively followed by spectral curves. Silver selenate gradually decomposes to a black selenide at ∼200°C.

Infrared and Raman spectra of polyethyleneglycol dimethylethers in the liquid state

Abstract: Infrared spectra of ethylene- through heptaethyleneglycol dimethylethers and Raman spectra of ethylene- through tetraethyleneglycol dimethylethers have been measured in the liquid state. Assignments of the vibrational frequencies have been made and the effect of the chain length on the spectra has been discussed with reference to the nature of vibrational modes. The CH2 rocking and the CO and CC stretching modes are appreciably coupled. In the liquid state the internal rotation angles (trans and gauche) about the CC and the CO bonds of the molecular chain are randomly distributed.

A high resolution investigation of the visible absorption spectrum of p-benzoquinone-H4 and -D4

Abstract: The visible absorption spectrum of p -benzoquinone is shown to consist of two electronic systems, an allowed (by spin-orbit interaction) 3 A u ← 1 A g system and an electronically forbidden 1 B 1 g ← 1 A g system. The latter is made vibronically allowed through the activity of two a u vibrations (a ring-twisting and a CH vibration) and one (or possibly two) b 3 u vibrations. The activity of the a u (CH) vibration contributes most of the intensity. These conclusions contradict previous analyses of the vapour spectrum but agree well with Sidman's conclusions from the low-temperature crystal spectrum [8]. The a u vibrations produce parallel bands which show regularly diverging R -branch heads from about K = 16 to K = 48. Computation of rotational contours for parallel and perpendicular bands, assuming that p -benzoquinone is a symmetric top (in fact κ = −0·79 in the ground state), has confirmed the identification of parallel bands and also aided the identification of perpendicular-type (type B) bands involving b 3 u vibrations. In the 1 B 1 g excited state the ∠HCC decreases by 12° and it is possible that Δ r cc = + 0·10A and Δ r cc = −0·09 A. There is no evidence for any deviation from planarity in either the 1 B 1 g or 3 A u excited states.

Non-planar vibration frequencies of anthracene

Abstract: A normal co-ordinate treatment of the vibrations of anthracene is carried out using a valency force field transferred from benzene. There have been previous partial assignments for only two of the four non-planar symmetry classes. Most of these are supported by the present calculations, which are of zero order.

Normal vibrations of dimers of aluminum trichloride, trimethyl aluminum and dimethyl aluminum chloride

Abstract: The calculation of normal vibrations of Al 2 Cl 6 , Al 2 Me 6 and Al 2 Me 4 Cl 2 has been made with a modified Urey—Bradley type potential. The force constants for Al 2 Cl 6 and Al 2 Me 6 have been calculated to agree with their observed frequencies. The frequencies of Al 2 Me 4 Cl 2 have been calculated with reference to the force constants transferred from those obtained for the two molecules. They are in satisfactory agreement with the observed values. The assigmnents of vibrational frequencies and the nature of ring modes are discussed on the basis of the calculations. The far infrared spectra of Al 2 Me 6 and Al 2 Et 6 in the region of 700-280 cm −1 were measured. The medium bands observed at 367 cm −1 for Al 2 Me 6 and at 338 cm −1 for Al 2 Et 6 have been assigned to one of the ring vibrations.