Analytical Chemistry Lecture 1 PDF

Analytical Chemistry Lecture 1 Analytical Chemistry  Definition Analytical chemistry is often described as the area of chemistry responsible for characterizing the composition of matter, both qualitatively (what is present) and quantitatively (how much is present). IN...

Analytical Chemistry Lecture 1 Analytical Chemistry  Definition Analytical chemistry is often described as the area of chemistry responsible for characterizing the composition of matter, both qualitatively (what is present) and quantitatively (how much is present). INFRARED SPECTROSCOPY IR  Learning Objectives To know analytical uses of infrared spectroscopy.✓ To understand the origin of electromagnetic radiation.✓  Uses of Infrared spectrum Qualitative:✓ Identification Structure elucidation. Quantitative.✓  Introduction in Spectroscopy and Electromagnetic Radiation Spectroscopy: Is a method of analysis based on the interaction of electromagnetic radiation and matter. Modern experimental chemistry uses many spectroscopic techniques : Ultraviolet and visible spectroscopy, infrared spectroscopy, and nuclear magnetic resonance spectroscopy. All depend in some manner on the absorption of energy by a molecule , the energy involved being in different regions of electromagnetic spectrum. Spectroscopy can involve any interaction between light and matter, including absorption, emission, scattering. Data obtained from spectroscopy is usually presented as a spectrum. How spectroscopy work? When a beam of electromagnetic radiation passes through a sample ,the photons interact with the sample , they may be absorbed,reflected,..etc. Absorbed radiation affects the electrons and chemical bonds in a sample. In some cases, the absorbed radiation leads to the emission. Emitted and absorbed spectra can be used to gain information about the material.  What Is Electromagnetic Radiation The optical properties of electromagnetic radiation, are explained best by describing light as a wave. Many of the interactions between electromagnetic radiation and matter, such as absorption and emission, however, are better described by treating light as a particle, or photon. Electromagnetic radiation : Consists of oscillating electric and magnetic fields that propagate through space along a linear path and with a constant velocity. When a sample absorbs electromagnetic radiation it undergoes a change in energy. The interaction between the sample and the electromagnetic radiation is easiest to understand if we assume that electromagnetic radiation consists of a beam of energetic particles called photons. When a photon is absorbed by a sample, it is “destroyed,” and its energy acquired by the sample. Electromagnetic radiation wavelength The distance between any two consecutive maxima or minima of an electromagnetic wave Wavenumber The reciprocal of wavelength. Wavenumbers are frequently used to characterize infrared radiation, with the units given in reciprocal centimeter (cm–1). Electromagnetic spectrum Absorbance of Electromagnetic Radiation In absorption spectroscopy a beam of electromagnetic radiation passes through a sample. Note: Energy is quantized and absorption of radiation causes a molecule to move to a higher internal energy level. Energy levels for a molecule are: Electronic>Vibrational>Rotational. Two general requirements must be met if an analyte is to absorb electromagnetic radiation. The first requirement is that there must be a mechanism by which the radiation’s electric field or magnetic field interacts with the analyte. For ultraviolet and visible radiation, this interaction involves the electronic energy of valence electrons. A chemical bond’s vibrational energy is altered by the absorbance of infrared radiation. The second requirement is that the energy of the electromagnetic radiation must exactly equal the difference in energy, DE, between two of the analytes quantized energy states.  IR Infrared Spectra for Molecules The energy of infrared radiation is sufficient to produce a change in the vibrational energy of a molecule. At room temperature most molecules are in their ground vibrational state (v = 0). A transition from the ground vibrational state to the first vibrational excited state (v = 1) requires the absorption of a photon. For example, a carbon–carbon single bond (C—C) absorbs infrared radiation at a lower energy than a carbon–carbon double bond (C=C) because a C—C bond is weaker than a C=C bond.  IR IR spectroscopy is a simple and rapid instrumental techniques that can give evidence for the presence of the various functional groups. IR spectroscopy deals with the interaction between a molecule and radiation from the IR region of the EM(Electromagnetic) spectrum (IR region =4000-400cm-1). Absorption of IR light causes changes in the vibrational motions of a molecule. IR radiation causes the excitation of the vibrations of bonds within that molecule. IR radiation is readily absorbed by molecular substances because photon energy in this region corresponds to the difference between vibrational energy states corresponding to stretching and bending. Note: Photons in the infrared region of the electromagnetic spectrum have ✓ Characteristic energies corresponding to those of molecular vibrations. IR region is subdivided into three regions: Near IR,mid IR,far IR Most of the IR used originate from the mid IR region Near IR,mid IR,far IR IR