CNGNGE JOHN MCMURRY CHAPTER 10 Structure Determination: Mass Spectrometry, Infrared Spectroscopy, H IRD EDITION and Ultraviolet Organic Chemistry with Biological applications Spectroscopy
CHAPTER 10 Structure Determination: Mass Spectrometry, Infrared Spectroscopy, and Ultraviolet Spectroscopy
Introduction Modern techniques for structure determination of organic compounds include: Mass spectrometry n Size and formula of the compound Infrared spectroscopy Functional groups present in the compound Ultraviolet spectroscopy Conjugated z electron system present in the compound Nuclear magnetic resonance spectroscopy Carbon-hydrogen framework of the compound
Modern techniques for structure determination of organic compounds include: ▪ Mass spectrometry ▪ Size and formula of the compound ▪ Infrared spectroscopy ▪ Functional groups present in the compound ▪ Ultraviolet spectroscopy ▪ Conjugated p electron system present in the compound ▪ Nuclear magnetic resonance spectroscopy ▪ Carbon-hydrogen framework of the compound Introduction
10-1 Mass Spectrometry of Small Molecules: Magnetic-Sector Instruments Mass spectrometry (MS)measures the mass and molecular weight (MW)of a molecule Provides structural information by finding the masses of fragments produced when molecules break apart Three basic parts of mass spectrometers: Sample Display Ionization source Mass analyzer Detector Electron impact(EI),or Magnetic sector,or Photomultiplier,or Electrospray ionization(ESI),or Time-of-flight(TOF),or Electron multiplier,or Matrix-assisted laser Quadrupole(Q) Micro-channel plate desorption ionization(MALDI) Cengge Leaming.All Rights Reserved
Mass spectrometry (MS) measures the mass and molecular weight (MW) of a molecule ▪ Provides structural information by finding the masses of fragments produced when molecules break apart ▪ Three basic parts of mass spectrometers: 10-1 Mass Spectrometry of Small Molecules: Magnetic-Sector Instruments
Mass Spectrometry of Small Molecules: Magnetic-Sector Instruments Electron-impact,magnetic- sector instrument Sample is vaporized into ionization source Magnet Ionsdeflected Bombarded by electron beam according to m/z (70 eV)dislodging valence Heated filament electron of sample producing cation-radical RH 。 RH+.+e- Sample Organic Cation molecule radical beam LCD display Most cation-radicals fragment and are separated in magnetic field according to their mass-to- charge ratio (m/z) Since z 1 for most ions the value of mz is mass of ion
Electron-impact, magneticsector instrument ▪ Sample is vaporized into ionization source ▪ Bombarded by electron beam (70 eV) dislodging valence electron of sample producing cation-radical ▪ Most cation-radicals fragment and are separated in magnetic field according to their mass-tocharge ratio (m/z) ▪ Since z = 1 for most ions the value of m/z is mass of ion Mass Spectrometry of Small Molecules: Magnetic-Sector Instruments
Mass Spectrometry of Small Molecules: Magnetic-Sector Instruments Mass spectrum of propane(C3Ha;MW=44) 100 80 -m/2=29 60 40 -m2=44 20 0 1020 40 60 80 100 120 140 m/2 Base peak Tallest peak Assigned intensity of 100% Base peak at m/z=29 in propane mass spectrum -Parent peak Unfragmented cation radical-molecular ion(M) Parent peak only 30%of base peak for propane
Mass spectrum of propane (C3H8 ; MW = 44) ▪ Base peak ▪ Tallest peak ▪ Assigned intensity of 100% ▪ Base peak at m/z = 29 in propane mass spectrum ▪ Parent peak ▪ Unfragmented cation radical – molecular ion (M+ ) ▪ Parent peak only 30% of base peak for propane Mass Spectrometry of Small Molecules: Magnetic-Sector Instruments