Introduction to organic spectroscopy Basic

spectroscopy intro

1. Introduction to Spectroscopy 1

2. What is Spectroscopy? Measurement of the amount of radiations absorbed by a substance at various wavelengths is called spectroscopy . OR Spectroscopy is the study of interaction of electromagnetic radiations with matter and measurement of absorption of radiations of various frequencies upon interaction with the matter. 2

3. Wavelength, λ : Distance between two adjacent crests and troughs of the wave in the beam of electromagnetic radiations. Units; angstrom, nanometer, micrometer and meter. Frequency, v : Number of waves passing a fixed point on the path of a beam of radiation per unit time. Units; Hertz (Hz) or cycle per second. Wavenumber, ῡ : Number of waves per centimeter. Its unit is cm-1. Energy, E: Every photon of specific radiation possesses exactly the same amount of energy which is, however different from the energy possessed by the photon of different radiations. The unit of energy commonly used is Joule. Parameters to characterize Electromagnetic radiations: Electromagnetic Radiation: From of energy: commonly known as radiant energy. Ordinary light: more visible form of radiant energy . 3

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5. Electromagnetic Spectrum: 5

6. Relation between Energy, frequency, wavelength and wavenumber. E = hv = hc/ λ = hc ῡ E = Energy h = planks constant v = frequency c = velocity of radiations λ = wavelength ῡ = wavenumber 7

7. Spectroscopic techniques Techniques Underlying principle Information obtained UV (200-400 nm) VIS (400-800 nm) Quantized absorption of UV/VIS radiations leading to electronic excitations. Presence and nature of unsaturation, particularly conjugation. IR (2.5-16 µm or 4000-625 cm-1) Quantized absorption of IR radiations leading to vibrational excitations. Presence and environment of functional groups, especially those containing X-H type bonds such a C-H, O-H and N-H or multiple bonds. NMR (60-6000 MHz) Quantized absorption of radio waves leading to transitions between different spin orientations of nuclei in the magnetic field. Environment of magnetically active nuclei, such as 1H, 13C etc., and number of nuclei of each type. MS (~70 eV ) Determination of mass-to-charge ratio and relative abundance of the ions formed on electronic bombardment of molecules. Molecular weight, molecular formula, molecular structure and isotopic abundance. 8

8. Elemental Analyzer Carbon Hydrogen & Nitrogen Analyzer can be used to determine the carbon, hydrogen and nitrogen content in coal, coke, food, soil, fertilizer, etcin the fields of power plant, coal mine, metallurgy, steel factory and so on.

9. Mass spectrometry Mass spectrometry (MS) is the study of ions created as a result of ionization/fragmentation as determined electrically in the gas phase (neutral molecules are not observed) Mass spectrometer

10. UV Spectrophotometer UV-visible spectrophotometer uses light over the ultraviolet range (185 - 400 nm) and visible range (400 - 700 nm) of electromagnetic radiation spectrum.

11. IR Spectrophotometer IR spectrophotometer: uses light over the infrared range (700 - 15000 nm) of electromagnetic radiation spectrum.

12. NMR Spectroscopy Nuclear magnetic resonance (NMR) spectroscopy is the study of molecules by recording the interaction of radiofrequency (Rf) electromagnetic radiations with the nuclei of molecules placed in a strong magnetic field. NMR machine

13. 15 Instrumentation: Detector Although different instruments are used for measuring absorbance in different spectral regions, in their simplest form they all consist of five main components: (1) source of electromagnetic radiations, (2) monochromator, (3) sample cell, (4) a detector and (5) readout device.