R. Norman Jones

The shapes and intensities of infrared absorption bands—A review

Abstract The experimental and theoretical factors influencing the measurement of the profiles and intensities of infrared absorption bands for materials in condensed states are reviewed. The effects of the spectral slit function and of the time constants of the spectrophotometer recording system on the band shape are discussed, and the methods available for the experimental evaluation of these quantities are described. The theoretical and experimental problems associated with the determination of the true band-intensity parameters from the corresponding apparent band-intensity parameters are examined critically and the interrelationships among the various spectrophotometric variables, including spectral slit width, amplifier time constant, scanning rate and amplifier gain are considered both in terms of the theory of errors and with respect to general laboratory practice.

FURTHER OBSERVATIONS ON THE USE OF INDENE FOR THE WAVENUMBER CALIBRATION OF INFRARED SPECTROMETERS

Abstract New values are reported for the positions of the absorption maxima in the infrared spectrum of indene containing 0·8% by weight of both camphor and cyclohexanone. The personal error in locating the maxima has been reduced by fitting polynomial series of the second, third and fourth degrees through five points in the neighborhood of the maxima, and computing the roots of the first derivatives, using a computer technique previously described. The peak values are compared with independent measurements made by P. J. Krueger on a different spectrometer. The peaks most suitable for calibration purposes have been selected on the basis of their distribution in the spectrum and the low r.m.s. variation in the computed positions of the maxima.

Infrared Spectrometry Applied to Steroid Structure and Metabolism

Publisher Summary This chapter illustrates how infrared spectrometry has been utilized in the elucidation of the structure of steroids and in steroid metabolism. The specificity of the infrared spectrum is finding application in connection with problems of steroid synthesis. It has made possible the detection and identification of individual steroids and, in combination with adsorption chromatography, has permitted qualitative and quantitative analyses of complex mixtures of steroids to be performed. By the application of these methods, a considerable number of new steroids have been isolated from human urine. The introduction of deuterium atoms modifies the infrared spectra of steroids and infrared spectrometry is a valuable supplement to mass spectrometry in the detection, analysis, and identification of deuterium enriched compounds. Correlations between the positions of certain of the absorption bands and the molecular structure have been established. These permit the presence of all the functional groups which commonly occur in steroids to be recognized. In the case of carbonyl groups and double bonds, more specific information can also be derived as to their location in the molecule. By the use of microtechniques, it has been made possible to obtain this information on quantities of material of the order of 25 μg.

A Reflecting Microscope for Infrared Spectrometry

A reflecting microscope designed for use in front of the entrance slit of a Perkin-Elmer single-beam infrared spectrometer is described. It is shown that the heating effect of the condensed beam on the sample is not significant except in the case of compounds which absorb strongly in the 3-micron region of the spectrum, and then only if the sample is unsupported. The instrument is being applied to the study of small quantities of material in solution and to single crystals. Spectra adequate for identification purposes may be obtained from less than 10 micrograms of a sample in solution. The minimum sample size is limited at present by the technique of sample transfer and if this can be improved, spectra could be obtained with about 1 microgram. Preliminary results using polarized radiation in the study of fatty acid crystals are also presented.

Computer Programs for Absorption Spectrophotometry

Brief descriptions are given of twenty-two modular computer programs for performing the basic numerical computations of absorption spectrophotometry. The programs, written in Fortran IV for card input and output, are available from the National Research Council of Canada. The input and output formats are standardized to permit easy interfacing to yield more complex data processing systems. Though these programs were developed for ir spectrophotometry, they are readily modified for use with digitized visual and uv spectrophotometers. The operations covered include ordinate and abscissal unit and scale interconversions, ordinate addition and subtraction, location of band maxima and minima, smoothing and differentiation, slit function convolution and deconvolution, band profile analysis and asymmetry quantification, Fourier transformation to time correlation curves, multiple overlapping band separation in terms of Cauchy (Lorentz), Gauss, Cauchy-Gauss product, and Cauchy-Gauss sum functions and cell path length determination from fringe spacing analysis.

The ultraviolet spectra of some methyl-substituted aromatic hydrocarbons

Abstract The ultraviolet absorption spectra of anthracene, phenanthrene, 3:4-benzphen-anthrene and several of their methyl and methylene derivatives have been measured at − 100°C in n-pentane solution and at room temperature in n-heptane solution. The effects of the position of methyl substitution on the band envelopes have been analysed. This work is in continuation of similar studies on methyl derivatives of 1:2-benzanthracene which have been described in a previous publication.

The use of indene for the calibration of small infrared spectrometers

Abstract Seventy-seven bands in the infrared spectrum of indene in the range 4000–690 cm −1 have been measured with an absolute precision varying from ±3 to ±0.2 cm −1 , using a grating spectrometer. Cyclohexanone and camphor (0.8 weight per cent) can be added to provide additional bands in the 1750–1700 cm −1 region without significantly displacing the position of the indene maxima that lie outside of this range. These liquid systems are chemically stable, provided they are stored in sealed ampules; they are recommended for the calibration of prism spectrometers.

Vibrational Spectroscopy of Liquid Crystals: IV. Infrared and Far Infrared Spectra of the MBBA and EBBA Liquid Crystals

Infrared spectra have been recorded for N(p-methoxy) benzylidene- (p-n-butyl) aniline (MBBA) and its ethoxy analog in the crystalline, mesomorphic and isotropic phases. From the spectra obtained fo...

Determination of deuterium in organic compounds by infrared spectrophotometry

Abstract The Trenner-Arison-Walker method for the micro-analysis of deuterium in organic compounds involves oxidation of the compound with copper oxide in a sealed tube, collection of the water by vacuum distillation, and analysis of the water by infrared spectrophotometry. Experience in applying this technique to a variety of organic compounds in our laboratory has suggested a number of procedural modifications. These principally affect the methods of sample handling and water collection. Difficulties associated with temperature changes on the spectrophotometry of the deuterium-enriched water are overcome by differential analysis against natural-abundance water using a double-beam spectrophotometer.

INFRARED INTENSITY MEASUREMENTS APPLIED TO THE DETERMINATION OF MOLECULAR STRUCTURE

Chemists have been using absorption spectra for many years as aids to the interpretation of the molecular structure of complex organic compounds. The spectra studied in the ultraviolet and visible regions are almost invariably reported on an absolute intensity basis of molecular extinction coefficient (emax.). The E , , , ~ . values are a useful means of distinguishing between different ultraviolet chromophores that absorb in the same region of the spectrum, and they are also useful for evaluating purity, particularly in following the isolation of pure compounds from natural sources. A few infrared spectroscopists, including Rose,’ Anderson and Seyfried,2 Hampton and N e ~ e l l , ~ RicMurry and T h ~ r n t o n , ~ Cross and Rolfe,6 and Reggiani, Casu, and Caroti,E have used molecular extinction coefficients, but it is still the general practice to express infrared band intensities in arbitrary units of percentage absorbed or percentage transmitted. For spectra measured in the solid phase as Nujol mulls or halide disks, the extinction coefficients cannot be determined, as there are no adequate methods to correct for scattering errors or for the nonhomogeneous distribution of the sample. However, for spectra measured in solution the molecular extinction coefficients can be evaluated in the same way as in the visible and ultraviolet regions of the spectrum. It has been recognized for a long time that measurements of infrared intensity are liable to greater errors than similar measurements made at higher frequencies, and it is often stated that infrared molecular extinction coefficients are subject to such large errors that they cannot usefully be transferred from one spectrometer to another. I t is true that there are instrumental factors that make it advisable, for the present, to report infrared intensities in “apparent” units; nevertheless, if proper precautions are taken in setting up and operating the spectrometer these errors need not be excessive. Our laboratory has been looking into this problem with respect to the measurement of both molecular extinction coefficients and integrated absorption intensities, and the reproducibility of such measurements on various types of spectrometers has been examined. The conclusions of this study will be mentioned briefly below and described in more detail in a forthcoming publication.? I t should be emphasized a t the outset that with the instruments now available, the recording of absolute intensity measurements is slow and