Group frequency correlation

The normal modes at the centre of the Brillouin zone, ( 4.3.1), (A = 0) can be deduced by a conventional factor group analysis [4,5]. Since there are two chains in the unit cell, equivalent modes on each chain couple to give an in-phase and out-of-phase pair of modes (Davydov splitting). Above 600 cm the modes can be described using standard group frequency correlations CH2 rock 720-1170 cm, C-C stretch... 

Compounds containing P—C Bonds. Vibrational data for CFgPXg, X = halogen or hydrogen, have been assigned on the basis of symmetry but there is considerable mixing of the internal co-ordinates of vibration, and simple group-frequency correlations cannot be made for all bands. 

The main purpose of a dynamical analysis of a molecule is to assign the vibrational transitions observed in infrared and Raman in terms of molecular motions. As mentioned above, chemical group frequency correlations have been the justification of most of the vibrational assignment. The description of the normal modes has posed some problems throughout the years. 

The first theoretical approach seeded by the explosive development of chemical spectroscopic group frequency correlations has been presented by King and Crawford who gave the dynamical conditions under which a normal mode can be defined as localized [38]. 

The reader is certainly familiar with the traditional group-frequency approach generally used in the past 50 years for the chemical application of the infrared spectra (Section 3.4). Correlation tables and books have been written which discuss group-frequency correlations and provide the way to carry out a chemical diagnosis from the vibrational spectrum (so far, the infrared spectra have enjoyed great popularity the reader is advised to extend their interest to the very useful and easily available Raman spectra). 

The message we wish to send to the reader of this book is that modern machines provide beautiful infrared and Raman spectra of polymers full of specific, unique and detailed information which can be extracted, not just merely and lazily using group frequency correlations. We will be very pleased to find that this book has provided the reader with enough motivation to overcome the potential barrier of some theoretical technicalities in order to enjoy fully the wealth of information inherently contained in the vibrational spectra of ordered or disordered chain molecules. 

In a few cases, enough spectra are presented of a group to illustrate a group frequency correlation. Examples of this would include groups such as methyl, tertiary butyl, phenyl, and a few others. Spectra 1-12 illustrate a spectra-structure correlation of a long chain aliphatic group. 

In this third edition, the general plan of the previous editions has been retained in order to provide a book that covers in one volume those aspects of vibrational spectroscopy that a chemical spectroscopist will find useful in the study of chemical structure or composition. This includes introductory theory of vibrational and rotational spectra, basic infrared instrumental components and experimental techniques, quantitative analysis, the use of symmetry in vibrational spectroscopy, and a detailed example of theoretical vibrational analysis. The most extensive part of this book (Chapters 4-13) is an in-depth study of group frequency correlations and how to use them in spectral interpretation. 

As in the case of infrared absorption spectroscopy, the bands in a Raman spectrum can be assigned through the use of group frequency correlation tables. Significant insight can be obtained from the compilations of functional group vibrational frequencies associated with infrared absorption spectroscopy, but... 

Infrared and Raman Spectra of Pristine Systems I. The infrared spectra of undoped oligomers and polymers do not show unusual features and can be interpreted with traditional group frequency correlations or with more detailed vibrational analysis. In contrast to what is observed in the Raman spectra, the infrared spectra show the expected vibrational transitions common to organic molecules. Vibrational frequencies are generally independent... 

Group frequency correlations for fluorocarbons are quite limited. It appears that interaction between vibrations occurs more extensively for fluorocarbons than for the corresponding hydrocarbons. Because of this it is difficult to find vibrations for fluorocarbons which remain constant for a series of compounds. Even though the extensive interaction of frequencies of fluorocarbons does not lead to good group frequency correlations, this interaction results in quite distinct spectra for each different type of fluorocarbon structure, so that small structural differences can often be detected by studying the infrared spectra of these compounds. 

Raman spectra have similar group frequency correlations, but two features are... 

Infrared spectroscopy is a widely used industrial tool for the structural and compos tionai analysis of organic, inorganic, or polymeric samples and for quality control of raw materials and commercial products. It is a relatively simple technique, non-destructive, versatile enough to handle solids, liquids and gases with a minimum of sample preparation, and accurate enough for both the qualitative identification of the structure of unknown materials and the quantitative measurement of the components in a complex mixture. An extensive body of literature on group frequency correlations exists as well as excellent reference spectral collections Instrumen-... 

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