CHEM 2211 1st Edition Lecture 8 Outline of Last Lecture I II III Ring flip with two substituents on a cyclohexane Fused cyclohexane rings Functional groups Outline of Current Lecture I II III IV Infrared Spectroscopy Infrared Spectrum Determining Functional Groups Reference Current Lecture I The Last Functional Groups and FT IR Vocabulary Infrared Spectroscopy Fourier transform IR Infrared Spectrum Function Group Region Absorption bands Fingerprint Region I II III IV V Infrared Spectroscopy A Infrared radiation is wavelengths 4000 600cm 1 B When infrared radiation IR strikes a molecular bond at the right frequency the molecule absorbs the radiation C This absorption of IR causes the molecule to bend and stretch a little bit more Infrared Spectrum A The IR spectrum is the graph produced when a sample molecule is bombarded with IR B It plots wavelength cm 1 vs transmittance C Each downward spike on the graph represents absorption and are called absorption bands D Fourier transform IR FT IR is the main type of spectrophotometer used today because of its speed and accuracy at measuring absorption Determining functional groups A The left portion of an IR spectrum 4000 1400 cm 1 is known as the functional group region because this region is similar among a functional group B The right side of the IR spectrum 1400 600 cm 1 is known as the fingerprint region because this region is unique to each molecule i For this class we only need to know the functional group region In depth discussion of the fingerprint region will happen in physical chemistry Absorption Band Intensity A A large change in dipole moment results in a high intensity absorption band B The more polar the more intense the absorption band Reference Type of Bond Carbon to Nitrogen TRIPLE bond Carbon to Carbon TRIPLE bond Carbon to Carbon DOUBLE bond Carbon to Nitrogen DOUBLE bond Benzene Carbon to Oxygen DOUBLE bond Carbon to Oxygen SINGLE bond Wavenumber cm 1 Intensity 2260 2220 Medium 2260 2100 Medium to weak 1680 1600 Medium 1650 1550 medium 1600 and 1500 1430 Strong to weak 1780 1650 Strong 1250 1050 Strong Carbon to Nitrogen SINGLE bond Oxygen to Hydrogen ALCOHOL Oxygen to Hydrogen CARBOXYLIC ACID 1230 1020 Medium 3650 3200 Strong Broad 330 2500 Strong Very Broad Nitrogen to Hydrogen 3500 3300 Medium Broad Carbon to Hydrogen 3300 2700 Medium
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