Organic Compounds FT-IR Spectroscopy

Adina Elena Segneanu, loan Gozescu, Anamaria Dabici, Paula Sfirloaga and Zoltan Szabadai National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara (INCEMC-Timisoara) 

From the point of view of analytical control of medicinal products, this domain is the most used. At the base of absorption is being generated electromagnetic radiation in this area spectral transitions are the vibrations of individual molecules or of crystalline network (if the sample examined is solid). Show effects such transitions caused by the vibrations of individual molecules provides information about molecular structure of the sample examined, and show effects such crystalline network to identify a particular forms of crystallization of the substance of interest. 

The most frequent use of the absorption spectrophototometry in the middle infrared field lies in the identification of substances through molecular vibration. The wavelength (i.e, the wave numbers) of the of the absorption band are characteristic chemical identity of the substance in question. The intensity of the absorption bands allows quantitative analysis of the samples but, unlike in the ultraviolet and visible, in the infrared field diffuse radiation is much more refreshing, and for this reason quantitative determination infrared, are affected by notable errors. 

From the standpoint of analytical use, the spectra of molecular vibration is enjoying increased popularity in comparison to the study of the crystal latice s vibrations. A molecule may be considered to be a vibrator with more than one degree of freedom, able to execute more modes of vibration. In each mode of vibration every atom in the molecule oscillates about their own position of equilibrium. Such oscillations have different amplitudes for 

A molecule composed of N atoms has several possible modes of oscillation. In each mode of oscillation (in principle) all the atoms of molecule perform periodic shifts aroxmd level position with a frequency of oscillation mode which is a feature of the assembly. Because each of the N atoms can run periodic shifts in 3 perpendicular directions each other, the assembly of N atoms can have 3N ways of motion. But, those displacements that correspond to moving molecule as a whole (not deform the geometry of the molecule) and movements, which correspond to entire molecules rotation about an axis (also without deforming the molecule s geometry), do not represent actual oscillation (associated with actual deformation of the molecule). 

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Product analyses for the reaction of CH3S with NO2 were carried out in order to elucidate the mechanism for that reaction in air. S0180 was observed by means of FT-IR spectroscopy when N0180 was used as a reactant. This is a clear evidence for the formation of CH3SO and NO as products of the above reaction. Dependence of the yield of SO2 on the initial concentration of O2 ana NO2 was observed, which indicates that the secondary reactions of CH3SO with 02 or NOz are important in the atmospheric oxidation of reduced organic sulfur compounds. 

The concentration-time behaviours of DMS and the reference organic compounds were followed over 30 - 35 min time periods by FT-IR spectroscopy. After acquiring 10 - 15 spectra of the mixture in dark (to control that no dark reaction takes place and to follow possible wall losses), the photooxidation was initiated by switching on the lamps (6 Philips TLA 40W) and then 15-20 spectra were recorded. Spectra were obtained by co-adding 64 scans which yielded a time resolution of 1 min. 

Nuclear magnetic resonance spectroscopy and Fourier transform infrared (FT-IR) spectroscopy are two common techniques for structural characterizations of organic compounds and polymers, and they have been widely used to characterize the... 

Fourier transform infrared spectroscopy (FT-IR) is useful for identifying organic and inorganic compounds by comparison with library references. Perkin Elmer System 2000 offers near IR, mid IR, far IR 15,000-15,030 cm, transmittance (T), specular reflectance (SR Ref. 6) and diffuse reflectance (DR), horizontal and vertical attenuated total reflectance (ATR) microscope (>10-gm spot, 10,000-10,580 cmy ... 

Infrared spectroscopy is probably the most widespread analytical spectroscopic technique for identification and characterization of organic compounds. Because of this identification capability infrared spectroscopy is desirable as a detection technique for chromatographic separations. With the advent of Fourier transform infrared spectroscopy/ the speed and sensitivity of infrared detection is greatly enhanced making such applications feasible. FT-IR detection has been widely accepted as a detector for gas chromatography (GC/FT-IR) (1) and has been applied with limited success to liquid chromatography (LC/FT-IR) (2)/ and more recently to supercritical fluid chromatography (SFC/FT-IR) (3). The recent review articles cited here provide excellent introduction and references to current state-of-the-art in these areas. 

Figure 1 MI/FT-IR spectra (fingerprint region) of (A) menthol, (B) neomenthol, (C) isomenthol and (D) neoisomenthol, 25 ng each. Reproduced with permission of the Society for Applied Spectroscopy from Coleman III WM and Gordon BM (1989) Examinations of the matrix isolation infrared spectra of organic compounds Part XIII. Applied Spectroscopy4Z 303.

The production of potassium bromide discs for IR spectroscopy has never been automated, although at least one scheme has indicated the possibility. When dispersive spectrometers were used, this did not matter so much as spectrum acquisition was of the same order of duration as sample preparation, but FT-IR machines are much more rapid. Thus diffuse reflectance has recently become a very popular technique for monitoring the IR spectra of organic compounds that are soluble in volatile solvents as it only requires the placing of a drop of solution on a sm l layer of ground alkali metal halide powder. 

See also ATR and Reflectance IR Spectroscopy, Applications Biochemical Applications of Raman Spectroscopy Food Science, Applications of Mass Spectrometry Food Science, Appiications of NMR Spectroscopy Fourier Transformation and Sampiing Theory FT-Raman Spectroscopy, Appiications iR Spectrometers, IR Spectroscopy Sample Preparation Methods IR Spectroscopy, Theory IR Spectral Group Frequencies of Organic Compounds Nonlinear Optical Properties Raman Optical Activity, Spectrometers Raman Spectrometers. 

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