Auburn University - CHEM 2080Organic Chem II Final Exam.

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Chapter 14: Infrared Spectroscopy and Mass Spectrometry IR Problems: 9, 10, 12, 14(a), 15, 16, 29, 36 (a,b,d,e), 37(a,d,e,f) Mass Spec: 18, 19, 20(a,b,c,) 22, 23, 24, 26, 27, 38, 39, 40, 43, 44, 47,... 48(a,b), 50, 60, 70 Both: 41, 46, 57, 58 14.2 IR Spectroscopy • Infrared radiation causes vibrational excitation of the bonds in a molecule o Bonds can stretch and bend (focus on stretching) • Identification of Functional Groups o The energy gap between vibrational states is dependent on the nature of the bond § ex: C—H and C—O bonds will both absorb IR radiation, but C—H will absorb a higher energy photon 14.3 Wavenumber • wavenumber of absorption associated with bond stretching is dependent on bond strength and mass of atoms sharing the bond • a bond’s wavenumber indicates its location on the IR spectra • IR spectra o Two main regions: § Diagnostic: fewer peaks, all the bonds that arise from double bonds, triple bonds, and X—H bonds • 4000-1500cm-1 § Fingerprint: signals resulting from vibrational excitation of single bonds • <1500cm-1 14.5 Signal Characteristics: Shape • Effects of Hydrogen Bonding o Hydrogen bonding weakens existing bonds, like those in O—H o These weakening effect causes alcohols to give rise to broad signals o When O—H bonds do not participate in hydrogen bonding it produces a narrow signal at 3600cm-1 o Two types of O—H bonds participating in hydrogen bonding § Alcohol: 3200-3600cm-1, strong and broad § Carboxylic Acid: 2200-3600cm-1, broad, more pronounced than alcohols [Show More]

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