Chapter 12: Mass Spectrometry, Infrared Spectroscopy, and Ultraviolet/VisibleSpectroscopyLearning Objectives:1. Be able to predict the fragmentation patterns expected to arise in the mass spectrum of alkanes, alkyl halides, ethers, alcohols, and ketones.2. Be able to describe what happens to a compound in a mass spectrometer3. Be able to use the mass spectrum of a compound to find the molecular mass, and to help identify the structure of a compound.4. Be able to describe what happens to a compound when it absorbs infrared radiation.5. Be able to use of a chart of functional group IR absorptions, and to help identify the structure of a compound.6. Be able to use result from elemental analysis to deduce the number of carbon, hydrogen, and nitrogen in the molecular formula.** Supplemental material, not included in the textbookSections:12.1 Mass Spectrometry12.2 The Mass Spectrum – Fragmentation12.3 Isotope in Mass Spectrometry12.4 High-Resolution Mass Spectrometry Can Reveal Molecular Formulas12.5 Fragmentation Patterns of Functional Groups*12.6 Spectroscopy and the Electromagnetic Spectrum#12.7 Infrared Spectroscopy12.8 Characteristic Infrared Absorption bands12.9 The Intensity of Absorption bands#12.10 The Position of Absorption bands12.11 The Position of an Absorption band Is Affected by Electron Delocalization, Electron Donation and Withdrawal, and Hydrogen Bonding.12.12 The Shape of Absorption Bands*12.13 Absence of Absorption Bands#12.14 Some Vibrations are Infrared Inactive12.15 A Lesson in Interpreting Infrared Spectra12.16 Ultraviolet and Visible Spectroscopy#12.17 The Beer-Lambert Law#12.18 The Effect of Conjugation on λmax#12.19 Visible Spectrum and Color#12.20 Some Uses of UV/VIS Spectroscopy#Additional material: Calculation of molecular formula using information from mass spectrometry and elemental analysis* Sections that will be focused1# Sections that will be skipped Recommended additional problems41, 43, 45, 54Class Note12.1 Mass Spectrometry and 12.2 The Mass Spectrum – FragmentationMmoleculeelectron beamM+emolecular ion(a radical cation)Cations detected by collector:fragmentationM (M-m)(M-n)mpnfragmentation(M-n-p)M (M-m) (M-n)(M-n-p)qfragmentation(M-m-q)qA. Most of the instrument is designed to detect cations.B. Relative abundance of fragmentation pattern depends on the energy of the electron beam.212.3 Isotope in Mass SpectrometryA. Relative abundance of carbon on molecular ion12C: 98.89% (0.989)13C: 1.11% (0.011)(M) (M+1)Each carbon contributes 0.011 abundance to the abundance of M+1 peak =>relative abundance of M+1 peak = (number of carbon in the analyzed molecule) x relative abundance of M x 0.011=> (number of carbon in the analyzed molecule) = relative abundance of M+1 peak ÷ (relative abundance of M x 0.011)* Not very accurate for compound with high molecular weightExample: M (150): 16.28 and (M+1) (151): 1.663B. Relative abundance of Cl on molecular ion35Cl: 75.77% (0.76)37Cl: 24.23% (0.24)(M) (M+2)For compound with one Cl: M/(M+2) ≈ 3/1relativeabundancem/z (m/e)M+(M+2)+(M-n)+Compound with one chloride(M-n+2)+n(M-n-Cl)+ClC. Relative abundance of Br on molecular ion479Br: 50.69% (0.51)81Br: 49.31% (0.49)(M) (M+2)For compound with one Br: M/(M+2) ≈ 1/1relativeabundancem/z (m/e)M+ (M+2)+(M-n)+Compound with one bromide(M-n+2)+n(M-n-Br)+Br12.4 High-Resolution Mass Spectrometry Can Reveal Molecular Formulas5Use Table 12.312.5 Fragmentation Patterns of Functional Groups*A. Alkyl halides (CH3CH2CH2Br and (CH3)2CHCl)B. Ethers (CH3CH2CH(CH3)OCH(CH3)2)6C. Alcohols (CH3CH2CH2CH2CH(OH)CH3)7D. Ketones (CH3CH2CH2COCH3)812.6 Spectroscopy and the Electromagnetic Spectrum#9Figure 12.1112.7 Infrared SpectroscopyFigure 12.12 (stretching and bending)12.8 Characteristic Infrared Absorption bandsTable 12.4 (OH, NH, and C=O)12.10 The Position of Absorption bands and 12.11 The Position of an Absorption bandIs Affected by Electron Delocalization, Electron Donation and Withdrawal, and Hydrogen Bonding.A. Effect of massB. Effect of bond order10D. Effect of resonance and inductive effectacyl halide > ester > aldehyde > ketone > amideE. C-H Absorption Bands11RC C H R2C CHH R2HC CH2HRHH RRRH Htranscis* NMR provides more reliable characterization. 12.12 The Shape of Absorption Bands*NH, NH2, OH, and CO2H12.14 Some Vibrations are Infrared Inactive1212.15 A Lesson in Interpreting Infrared SpectraC=O and H-bondAdditional material: Calculation of molecular formula using information from massspectrometry and elemental analysis13A. Example 1From Mass Spec M+: 99From elemental analysis: C: 60.5%; H: 9.1%; N: 14.1%B. Example 2From Mass Spec M+: 142, relative intensity: (M+/(M+2)+ = 100/35From elemental analysis: C: 58.9%; H: