Infra red spectra

IR radiation is absorbed by a molecule when it has the same frequency as that of one of the molecular vibrations, provided the latter is associated with a change of molecular dipole moment. The IR absorption spectrum of a molecule is thus highly characteristic, and it can usually be used as a molecular fingerprint. In addition to use for identification purposes, the absorption of radiation at 

If a specific bond or atomic gronping is present it can be expected to prodnce an absorption peak somewhere within the characteristic range indicated on the chart. In spite of considerable overlap between some of these characteristic ranges, IR spectra have, in practice, proved very nsefnl for identification and characterisation of individual compounds, or confirmation of the presence of a particular chemical linkage. Particularly useful for structural diagnosis are the following absorption ranges (cm )  

Within particular families of phosphorus compounds, the characteristic absorption ranges are often narrower than indicated above or on the chart. Other correlations are available, although some, such as for P-C or P-N, are of limited diagnostic value because of their variable position and overlap with other ranges. 

Multiple bonds usually absorb at higher frequencies (cm ) than their single bond counterparts, for example. 

Lower absorption frequencies are to be expected when heavier atoms are involved  

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Bellamy, The Infra-Red Spectra of Complex Molecules, 1954 (Methuen). Randall, Fowler, Fuson and Dangl, Infrared Determination of Organic Structures, 1942 (Van Nostrand). 

Although no chemical reaction occurs, measurements of the freezing point and infra-red spectra show that nitric acid forms i i molecular complexes with acetic acid , ether and dioxan. In contrast, the infrared spectrum of nitric acid in chloroform and carbon tetrachloride - is very similar to that of nitric acid vapour, showing that in these cases a close association with the solvent does not occur. 

When mixed with Lewis acids, dinitrogen pentoxide yields crystalline white solids, which were identified as the corresponding nitronium salts by their infra-red spectra. The reaction with boron trifluoride can be formulated in the following way... 

An investigation of the infra-red spectra of mixtures of nitric acid and acetic anhydride supports these conclusions. The concentration of nitronium ions, measured by the absorption band at 2380 cm, was... 

C. D. Craver, Infra-Red Spectra of Plasticicyers and Other Additives, 2nd ed.. The Coblentz Society, Kirkwood, Mo., 1980. 

Measurements. Infra-red spectra for the region 600-4000 cm-1 were measured with a Perkin-Elmer Model 710B spectrometer on samples pressed in KBr pellets. Magnetic susceptibilities were measured with a vibrating sample magnetometer (Princeton Applied Physics) as previously described.(4)... 

Infra-red Spectra of Deuterium-labelled Carbohydrates, S. A. Barker, R. H. Moore, M. Stacey, and D. H. Whiffen, Nature, 186 (1960) 307-308. 

Ahlers, N. H. Eand S. P. Ligthelm The Infra-red Spectra of Methyl... 

L. J. Bellamy, Infra-Red Spectra of Complex Molecules, 2nd edn., John Wiley and Sons, New York, 1975. 

Infra-red, microwave, and X-ray photoelectron spectroscopy Infra-red and ultra-violet spectroscopy has been widely used for investigating the structure of intermolecularly hydrogen-bonded complexes in the solid state (Novak, 1974) and in solution (Zundel, 1976, 1978 Clements et al., 1971a,b,c Pawlak et al., 1984). By analysing the infra-red spectra of equimolar liquid mixtures of amines with formic or acetic acid, the relative importance of structures [10] and [11] was estimated (Lindemann and Zundel, 1977). It was proposed that [10] and [11] make equal contributions to the observed structure of the complex when the p -value of the carboxylic acid is approximately two units lower than that of the protonated amine. 

Structures for the hydrogen-bonded species [12], [13], and [14] have been suggested on the basis of their infra-red spectra in solution (Clements et al.,... 

Bellamy, L.J. (1975). The Infra-red Spectra of Complex Molecules, Chapter 11, p. 203, Chapman and Hall, London... 

Each dip in the spectrum is called a band or peak. The transmittance is 0 % if all the radiation is absorbed and with no absorption the transmittance is 100%. The absorption of infrared radiations can be expressed either in terms of wave length (A.) or in wave number (y). Mostly infra red spectra of organic compounds are plotted as percentage transmittance against wave number. The relationship between wave length and wave number is as follows ... 

It has been found that no two compounds except the enantioners have similar infra red spectra. 

In the symmetric one, since there is no change in the dipole moment, it is not seen in the infra red spectra but there is also an asymmetric vibration, one oxygen atom approaches the carbon atom and the other moves away. Thus this asymmetrical stretching appears in the infrared spectrum in the region 2330 cm-1. 

It will be obvious from my account that although I consider myself primarily a physical chemist, my concern was always with finding the most efficient solution to a problem. If that meant doing phase-rule studies with a vacuum line (hardly ever attempted before), or getting infra-red spectra of polymers to identify end-groups when the only IR instrument in the City of Manchester at that time was in the ICI laboratories at Blackley, or synthesising new model compounds or super-pure A1C13, we just overcame the practical obstacles and got on with it. 

Infra-red spectra of charge-transfer salts as contact (inner-sphere) ion pairs in the solid state and in solution... 

Allen, R. J. L. (1940). Micro-determination of phosphorus. (Colorimetric estimation molybdate blue.) Biochem. J. 34, 858. Bellamy, L. J. (1954). Infra-red Spectra of Complex Molecules. Methuen and Co. 

Holmstead, B. and Larson, L. (1951). Infra-red spectra of some organic phosphoryl compounds. Acta Chem. Scand. 5, 1179. 

Cole, A. R. H. Infra-red Spectra of Natural Products. Part II. Compounds... 

The infra-red spectra of the trimethyl, dimethyl- and dimethylethyl-carbonium salts in excess antimony pentaduoride are shown in Figs. 4a, b, and c. The IRTRAN cells used are not transparent below 770 cm , thus obscuring the 650 cm SblY absorption which would, however, be overlapped by the solvent SbFs absorption. The broad, intense absorption band which appears in all the spectra near 1550 cm is present in the solvent spectrum. It was found to be dependent on the purity of the SbFs, but the nature of the impurity was not established. It should also be mentioned that Deno found an intense absorption at 1533 cm in cyclohexenyl cations thus, secondary carbonium ions formed from the reaction with olefins (which arise from deprotonation) could add to this broad absorption. 

Using assumed molecular models and force constants based on the force constants derived from the paraffin series, normal co-ordinate calculations for the simple alkylcarbonium ions were carried out. These calculations were made in order to predict the vibrational spectra. Comparison with the experimentally obtained infra-red spectra show that the main observed features can indeed be reasonably explained in terms of the modes calculated for the planar models of the ions and allowed an assignment of the fundamentals (Table 11). 

The following conclusions can be established from the infra-red spectra ... 

Davis, M.. and G. H. Thomas. The lattice energies, infra-red spectra, and possible cyclization of some dicarboxylk acids. Trans. Faraday Soc. 56 185-192, 1960. 

The ultra-violet spectra of guanidines have often been determined in connection with the measurements of dissociation constants [17, 38,41], and other studies have been repotted [42-44]. There have been many reports on the infra-red spectra [31, 35, 42, 45-48], the nuclear magnetic resonance spectra [38, 49-51] (see also p. 134), the Raman spectra [52-54], force constants [35, 36], and mass spectra [55] of substituted guanidines. 

As was mentioned in the preceding section, the infra-red stretching vibration bands of chalcogenoanions appear usually as more or less smeared-out bands. In contrcist, the infra-red spectra of small amounts of polyatomic anions isolated in eilkah halide host lattices have very sharp bands [see results in Refs. 204—209)]. Thus, one can clearly see that the bands are better defined when the anion can be effectively isolated and thereby ehminate the coupling between neighboring identical ions as well as reducing the other effects discussed earlier. More will be said about this in the next section. 

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