Infrared Spectroscopy Review PDF

International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 International Journal of Research Publication and Reviews Journal homepage: www.ijrpr.com ISSN 2582-7421 Review Article AN OVERVIEW ON I...

International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 International Journal of Research Publication and Reviews Journal homepage: www.ijrpr.com ISSN 2582-7421 Review Article AN OVERVIEW ON INFRARED SPECTROSCOPY KARTHIKA.B. R*1, Mr. NISHAD V.M * 2, Dr. PRASOBH G.R*3 1 B.Pharm student, Sree Krishna College of Pharmacy and Research Centre,Parassala, Thiruvananthapuram, Kerala, India. 695502 2 Associate professor, Sree Krishna College of Pharmacy and Research Centre, Parassala,Thiruvananthapuram, Kerala, India. 695502 3 Principal, Sree Krishna College of Pharmacy and Research Centre, Parassala, Thiruvananthapuram, Kerala, India. 695502 ABSRACT This review mainly focuses on the principal, instrumentation, interpretation, application of infrared spectroscopy. Infrared (IR) radiation refers broadly to that part of the electromagnetic spectrum between the visible and microwave region. Of greatest practical use to the organic chemist is the limited portion between 4000 and 400cm -1. Infrared spectroscopy monitors the interaction of functional groups in chemical molecules with infrared light resulting predictable vibrations that provides a “fingerprint” characteristic of chemical or biochemical substances present in the sample. Infrared spectroscopy is a technique that probes the vibrations within a material. Infrared spectroscopy has always been a powerful tool for the identification of organic materials. The development of Fourier transform infrared (FTIR) spectroscopy has introduced a popular method for the quantitative analysis of complex mixtures, as well as for the investigation of surface and interfacial phenomena. KEY WORDS- IR, FTIR *Author for correspondence: Karthika B.R Sree Krishna College of Pharmacy and Research Centre, Parassala,Thiruvananthapuram, Kerala, India.695502 E-mail: [email protected]  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 527 INTRODUCTION Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or functional groups in solid, liquid, or gaseous forms. The method or technique of infrared spectroscopy is conducted with an instrument called an infrared spectrometer (or spectrophotometer) which produces an infrared spectrum. An IR spectrum can be visualized in a graph of infrared light absorbance (or transmittance) on the vertical axis v/s frequency or wavelength on the horizontal axis. Typical units of frequency used in IR spectra are reciprocal centimetres (sometimes called wave numbers), with the symbol cm−1. Units of IR wavelength are commonly given in micrometres (formerly called "microns"), symbol μm, which are related to wave numbers in a reciprocal way. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectroscopy. Infrared (IR) radiation refers broadly to that part of the electromagnetic spectrum between the visible and microwave region. Of greatest practical use to the organic chemist is the limited portion between 4000 and 400cm -1. There has been sum interest in the near-IR (14,290-4000cm-1) and the far-IR region (700-200cm-1) Although the IR spectrum is characteristics of the entire molecule, it is through that certain groups of atoms give rise to bands at or near the same frequency regard less of the structure of the rest of the molecule. It is the persistence of these characteristics band that permits the chemist to obtain useful structural information by simple inspection and reference to generalized charts of characteristics group frequencies. HISTORY Chemical IR spectroscopy was emerged as a science in 1800 by Sir William Herschel. Michelson invented interferometer in 1881. Infrared spectrometers have been commercially available since the 1940s. At that time, the instruments relied on prisms to act as dispersive elements, but by the mid 1950s, diffraction gratings had been introduced into dispersive machines. The most significant advances in infrared spectroscopy, however ,have come about as a result of the introduction of Fourier-transform spectrometers. In 1960 Cooley -Turkey  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 528 developed an algorithm which quickly does a Fourier transform.This type of instrument employs an interferometer and exploits the well-established mathematical process of Fourier-transformation. PRINCIPLE Infrared radiation of frequencies less than about 100cm-1 is absorbed and converted by an organic molecule into energy monocular rotation. These absorptions is quantized; thus a molecular rotation spectrum consist discrete lines. IR radiation in the range from about 10000 -100cm-1 is absorbed and converted by an organic molecule into energy of molecular vibration. This absorption is also quantized, but vibration spectra appear as bands rather than as lines because a single vibrational energy change is accompanied by a number of rotational energy changes. It is with these vibrational- rotational band, particularly those occurring between 4000 and 400cm-1. The frequency or wavelength of absorption depends on the relative masses of the atoms, the force constants of the bonds, and the geometry of the atoms. This technique is based upon the simple fact that a chemical substance show marked selective absorption in the infrared region.after absorption of IR radiation , the molecule of the chemical substance vibrates at many rates of vibration, giving rise to close packed absorption bands ,called an IR absorption spectrum which may extend over a wide wavelength range. Various bands will be present in the IR spectrum which will corresponding to the characteristic functional group and bond present in the chemical substance. Thus, an IR spectrum of a chemical substance is a fingerprint for its identifications. Frequency, ν (nu), is the number of wave cycles that pass through a point in one second. It is measured in Hz, where 1 Hz = 1 cycle/sec. Wavelength, λ (lambda), is the length of one complete wave cycle. It is often measured in cm (centimetres). Wavelength and frequency are inversely related:  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 529 ν =c/λ and λ=c/v where c is the speed of light, 3 x 1010 cm/sec Energy is related to wavelength and frequency by the following formulas: E= h v = h c/λ where h = Planck‟s constant, 6.6 x 10–34 joules-sec Note that energy is directly proportional to frequency and inversely proportional to wavelength. The IR region is divided into three regions: the near, mid, and far IR. The mid IR region is of greatest practical use to the organic chemist. This is the region of wavelengths between 3 x10 -4and 3x 10 -3 cm. Chemists prefer to work with numbers which are easy to write; therefore, IR spectra are sometimes reported in µm, although another unit, ν (nu bar or wavenumber), is currently preferred. A wavenumber is the inverse of the wavelength in cm: v--- = 1/λ where ν is in units of cm–1, λ is in units of cm and now; E = h c ν- In wavenumbers, the mid IR range is 4000–400 cm–1. An increase inwavenumber corresponds to an increase in energy. Infrared radiation is absorbed by organic molecules and converted into energy of molecular vibration. In IR spectroscopy, an organic molecule is exposed to infrared radiation. When the radiant energy matches the energy of a specific molecular vibration, absorption occurs. The wavenumber, plotted on the X-axis, is proportional to energy; therefore, the highest energy vibrations are on the left. The percent transmittance (%T) is plotted on the Y- axis. An absorption of radiant energy is therefore represented by a “trough” in the curve: zero transmittance corresponds to 100% absorption of light at that wavelength. Band intensities in IR spectrum may be expressed either as transmittance (T), or absorbance (A). transmittance is defined as the ratio of radiant power transmitted by a sample  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 530 to the radiant power incident on the sample. On the other hand, absorbance is defined as the logarithm, to the base, 10, of the reciprocal of transmittance, i.e., A=log10 (1/T) RANGE OF INFRARED REGIONS Region wavelength (λ), µm wavenumbers (v--) frequencies cm-1 (v), Hz Near 0.78 to 2.5 12800 to 4000 3.8 x 1014 to 1.2 x 1014 Middle 2.5 to 50 4000 to 200 1.2 x 10 14 to 6.0 x 1012 Far 50 to 1000 200 to 10 6.0 x 10 12 to 3.0 x 1011 Most used 2.5 to 15 4000 to 670 1.2 x 1014 to 2.0 x 1013 Near-Infrared Region  In the near-infrared (NIR) region, which meets the visible region at about 12,500cm- 1 (0.8micrometer) and extend to about 4000cm-1(2.50micrometer), there are many absorption band that result from harmonic overtones of fundamental and combination band often associated with hydrogen atoms.  The first overtones of the O-H and N-H stretching vibration near 7140cm-1 and 6667cm-1 respectively, and combination band that result from the C-H stretching and deformation vibration of alkyl group at 4548cm-1 and 3850cm-1.  The absorptivity of near infrared bands is from 10-1000 times less than that of mid infrared bands.  Thicker sample layer (0.5-10mm) compensates for this smaller molar absorptivity. Because the absorptivity is so low, the NIR beam penetrate deeper into a sample in reflectance techniques, giving a more representative analysis.  Near infrared spectroscopy is valuable tool for the analyzing mixture of the aromatic amines.  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 531  Primary aromatic amines are characterised by two relatively intense absorption band near 1.97 and 1.49μm.  The band at 1.97μm is combination of N-H bending and stretching modes.  1.49μm is the first over tone of the symmetric N-H stretching vibrations.  Secondary amines exhibit an over tone band but do not absorb appreciably in the combination region. These difference in absorption provide the basic for the rapid quantitative analytical methods. The analyses are normally carried out on 1% solutions in CCl4 using 10-cm cells. Background correction are obtained at 1.575 and 1.915μm.  Tertiary amine does not exhibit appreciable absorption at either wavelength. The overtone and combination bands of aliphatic amines are shifted to about 1.525and 2.000μm respectively.  Near infrared reflectance spectra find wide acceptance in the food and grain industry for the determination of protein, fat, moisture, sugar, oils, iodine number etc.  NIR reflectance spectra have also been used for the determination of the substance in wood, components of polymer, and even geological exploration from aircraft. The intensities are weak but measurable and reproducible. Mid -infrared region  This region is divided into, 1. Group frequency region, 4000-1300cm-1(2.50-7.69μm). 2. Fingerprint region, 1300-650cm-1(7.69-15.38µm).  In the group frequency region the principle absorption bands are assigned to vibration units consisting of only two atoms of a molecule that is , units that are more or less dependent on only the functional group that gives the absorption and not on the complete molecular structure. Structural influence does reveal themselves, however, as significant shift from one compound to another.  The C-H stretching frequencies are especially helpful in establishing the type of compound present, for example, # C Ξ C-H occur around 3300cm-1(3.03µm) # aromatic and unsaturated compounds around 3000-3100cm-1(3.33-3.23µm) # Aliphatic compound at 3000-2800cm-1(3.33-3.57µm)  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 532  The intermediate frequency range ,2500-1540cm-1 is often called the unsaturated region. Triple bonds, and very little else, appear from 2500-2000cm-1. Double bond frequencies fall in the region from 2000-1540cm-1.  By judicious application of accumulated empirical data, it is possible to distinguish among C=O, C=C, C=N, N=O, and S=O bands.  The major factors in the spectrum between 1300 and 650cm-1 are single bond stretching frequencies and bending vibration of polyatomic system that involve motions of bonds linking a substituent group to the remainder of the molecule. this is the fingerprint region. Far infrared region  The region 667-10cm-1(15.0-1000µm) contains the bending vibration of carbon, nitrogen, oxygen and fluorine with atom heavier than mass 19, and additional bending motions in cyclic or unsaturated systems.  The low frequency molecular vibration in the far infrared are particularly sensitive to changes in the overall structure of the molecule; thus, the far infrared bands often differ in a predictable manner for different isomeric forms of the same basic compound.  The infrared frequency of the organometallic compounds is often sensitive to the metal ion or atom.  This region mainly used for the study of the organometallic or inorganic compounds. MOLECULAR VIBRATIONS The relative position of atoms in a molecule are not fixed but instead fluctuate continuously because of a multitude of different types of vibrations and rotations about the bonds in the molecules. For a simple diatomic or triatomic molecule, it is easy to define the number and nature of such vibrations and relate these to energies of absorption. An analysis of these kind becomes difficult if not impossible for molecule made up of many atoms. Not only do large molecule have a large no. of vibrating centers, but also interactions among several centers can occur and must be considered for a complete analysis. Vibration falls into two categories,  Stretching vibration.  Bending vibration. Stretching vibration: A stretching vibration involves a continuous change in the interatomic distance along the axis of the bond between two atoms.  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 533 a). Symmetric stretching The atoms of a molecule either move away or towards the central atom, but in the same direction. b) Asymmetrical stretching One atom approach towards the central atom which other departs from it.. Bending vibration : They involve the movement of atoms which are attached to a common central atom, such that there is change in the bond axis and bond angle of each individual atom without change in their bond length.  Bending vibrations generally required less energy and occur at longer wavelength than stretching vibration.  Bending vibrations are of two types: 1. In plane bending 2. Out plane bending a) In plane bending vibration Rocking: in plane bending of an atom occur where in they swing back and forth with respect to central atom. Scissoring: in the plane bending of atoms occur where in they move back and forth that is, theyapproach to each other. b) Out plane blending : Wagging: two atoms oscillate up and below the plane with respect to central atom. Twisting: one of the atoms moved up the plane while other down the pane with respect to the central atom. INSTRUMENTATION OF INFRARED (IR) SPECTROSCOPY The usual optical materials, glass or quarts absorb strongly in the infrared region consequently the apparatus for measuring infrared spectra is appreciably different from that for the visible ultraviolet regions. The main part of an IR spectrometer are as follows  IR radiation sources  Monochromators.  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 534  Sample cells and sampling of substances.  Detectors. The IR Radiation Sources. In common with other types of absorption spectrometers, infrared instruments require a source of radiant energy which provides a means for isolation narrow frequency bands. The radiation source must emit IR radiation which must be (i) Intensive enough for detection (ii) Steady (iii) Extend over the desired wavelength Although these radiations are continuous, only selected frequencies will be absorbed by the sample. The various popular sources of IR radiations are: (a)Incandescent lamp: In the near infrared instruments an ordinary incandescent lamp is generally used. However, this fails in the far infrared because is it glass enclosed and has low spectral emissivity. (b)Nernst Glower: It consists of a hollow rod which is about 2mm in diameter and 30mm in length. The glower composed of rare earth oxides as zirconia, yttria and thoria. Nernst glower is non- conducting at room temperature and must be heated by external means to bring it to a conducting state. Glower is generally heated temperature between 1000 to 18000C. It provides maximum radiation at about 7100 cm-1 (1.4µ). The main disadvantage Nernst glower is that is emit IR radiation over wide wavelength range; the intensity of radiation remains steady and constant over long periods of time. One main disadvantage of Nernst is its frequent mechanical failure. Another disadvantage is that its energy also concentrated in the near infrared regions of the spectra. (c) Globar source: It is a rod of sintered silicon carbide which is about 50mm in the length and 4mm in diameter. When it is heated to a temperature between 1300 and 17000C, it strongly emits radiation in the IR region. It emits maximum radiation at 5200 cm-1.  International Journal of Research Publication and Reviews, Vol 3, no 4, pp 526-552, March 2022 535 Unlike the Nernst glower, it is self-starting. As its temperature coefficient positive, it have been conveniently controlled with variable transformer. Unlike the Nernst glower, it is more satisfactory, for it work at wavelengths longer than 650 cm-1 (0.15µ). The main disadvantage is that it is a less intense source than the Nernst glower. (d)Mercury Arc: In the far infrared region (wave number