INFRARED SPECTROSCOPY: INFRARED SPECTROSCOPY BY CH.ARJUN M.PHARM 1 st YEAR PHARMACEUTICAL ANALYSIS CONTENTS: CONTENTS Theory and principle Types of vibrations Instrumentation FTIR Interference of IR spectra Applications THEORY: THEORY Infra red spectroscopy is also called as vibrational spectroscopy The study of absorption of infrared radiation, which results in vibrational transitions of I.R spectra. It is mainly used for structural elucidation to determine the functional groups The ranges of infrared radiations are Very near IR radiation:1.2-2.5µ Mid IR radiation:2.5-25µ Far IR radiation:25-400µ TYPES OF VIBRATIONS: TYPES OF VIBRATIONS There are two types of vibrations Stretching vibrations These are the vibrations in which bond length is altered i.e. increase or decrease .There are two types Symmetrical stretching: in which two bonds increase or decrease, symmetrically. Asymmetrical stretching: in which one bond length increase the other one decrease Slide 5: Bending vibrations : In-plane bending: In these vibrations there is change in bond angle. Bending of bonds takes place with in the plane. Scissoring: In which bond angle decreases Rocking: in which bond angle is maintained,but bond moves within the plane Out-plane bending :(out side plane of the molecule) Wagging: In which both atoms move to one side of the plane Twisting: In which one atom is above the plane and the other is below the plane INSTRUMENTATION: INSTRUMENTATION The main parts of IR spectrometre are : IR radiation sources Incandescent lamp Nernst glower Globar source Mercury arc Slide 8: Monochromators Prism monochromators Grating monochromators Sampling methods Sampling of solids Solids run in solution Solid films Mull technique Pressed pellet technique Slide 9: Sampling of liquids: 2t=N/w 1 -w 2 Sampling of gases Detectors: Bolometres Thermocouple Thermistor Golay cell Photo conductivity cell Pyroelectric detectors Slide 10: Golay cell FTIR: FTIR Slide 12: Dispersive IR FTIR Many moving parts only mirror moves Stray light –spurious readings Stray light does not effect Small amount of IR beam Large amount of IR beam Narrow frequency range falls on the detector All frequency falls on the detector Scan the sample slowly It is rapid Sample undergoes thermal effect It doesn’t occurs SPECTRAL INTERFERENCE: SPECTRAL INTERFERENCE IR spectra of ALKANES C—H bond “saturated” (sp 3 ) 2850-2960 cm -1 + 1350-1470 cm -1 -CH 2 - + 1430-1470 -CH 3 + “ and 1375 -CH(CH 3 ) 2 + “ and 1370, 1385 -C(CH 3 ) 3 + “ and 1370(s), 1395 (m) Slide 15: IR of ALKENES =C—H bond, “unsaturated” vinyl (sp 2 ) 3020-3080 cm -1 + 675-1000 RCH=CH 2 + 910-920 & 990-1000 R 2 C=CH 2 + 880-900 cis -RCH=CHR + 675-730 (v) trans -RCH=CHR + 965-975 C=C bond 1640-1680 cm -1 (v) Slide 17: IR spectra BENZENE s =C—H bond, “unsaturated” “aryl” (sp 2 ) 3000-3100 cm -1 + 690-840 mono-substituted + 690-710, 730-770 ortho -disubstituted + 735-770 meta - disubstituted + 690-710, 750-810(m) para -disubstituted + 810-840(m) C=C bond 1500, 1600 cm -1 APPLICATIONS: APPLICATIONS For organic compounds: Identification of substance like ( hydrocarbons.hydroxy compounds,aldehydes and ketomes,carboxylic groups,amines etc) Determination of molecular structure Studying the progress of the reaction Detection of impurities For in organic compounds: High modes of vibrations Lower symmetry of complexes Formation of chelates Geometrical isomerism REFERENCE: REFERENCE INSTRUMENTAL METHOD OF CHEMICAL ANALYSIS,GURUDEEP R CHATWAL,SHAM K ANAND.