CHEM 2211 1st Edition Lecture 8 Outline of Last LectureI. Ring flip with two substituents on a cyclohexaneII. Fused cyclohexane ringsIII. Functional groupsOutline of Current LectureI. Infrared SpectroscopyII. Infrared SpectrumIII. Determining Functional GroupsIV. ReferenceCurrent LectureI. The Last Functional Groups and FT-IRVocabularyInfrared SpectroscopyInfrared SpectrumAbsorption bandsFourier transform IRFunction Group RegionFingerprint RegionI. Infrared SpectroscopyA. Infrared radiation is wavelengths 4000-600cm-1B. When infrared radiation (IR) strikes a molecular bond at the right frequency, the molecule absorbs the radiationC. This absorption of IR causes the molecule to bend and stretch a little bit moreII. Infrared SpectrumA. The IR spectrum is the graph produced when a sample molecule is bombarded with IR.B. It plots wavelength (cm-1) vs % transmittanceC. Each downward spike on the graph represents absorption and are called absorption bandsD. Fourier transform IR (FT-IR) is the main type of spectrophotometer used today because of its speed and accuracy at measuring absorptionIII. Determining functional groupsA. 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 groupB. The right side of the IR spectrum (1400-600 cm-1) is known as the fingerprint region because this region is unique to each moleculei. For this class we only need to know the functional group region. In-depth discussion of the fingerprint region will happen in physical chemistryIV. Absorption Band IntensityA. A large change in dipole moment results in a high intensity absorption bandB. The more polar the more intense the absorption bandV. ReferenceType of Bond Wavenumber (cm-1) IntensityCarbon to NitrogenTRIPLE bond2260-2220 MediumCarbon to CarbonTRIPLE bond2260-2100 Medium to weakCarbon to CarbonDOUBLE bond1680-1600 MediumCarbon to NitrogenDOUBLE bond1650-1550 mediumBenzene ~1600 and ~1500-1430 Strong to weakCarbon to OxygenDOUBLE bond1780-1650 StrongCarbon to OxygenSINGLE bond1250-1050 StrongCarbon to NitrogenSINGLE bond1230-1020 MediumOxygen to HydrogenALCOHOL3650-3200 Strong, BroadOxygen to HydrogenCARBOXYLIC ACID330-2500 Strong, Very BroadNitrogen to Hydrogen 3500-3300 Medium, BroadCarbon to Hydrogen 3300-2700
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