UH CHEM 3331 - infrared spectroscopy, mass spectrometry (2 pages)

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infrared spectroscopy, mass spectrometry

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infrared spectroscopy, mass spectrometry


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University of Houston
Chem 3331 - Organic Chemistry
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CHEM 3331 1nd Edition Lecture 26 Outline of Last Lecture I Reaction with PX3 or PX5 II Reaction with thionyl chloride III Dehydration IV Reaction of diols V Formation of esters Outline of Current Lecture I Mass spectrometry II Electromagnetic spectrum III Infrared spectroscopy Current Lecture I Mass spectrometry Through combustion we can determine the ratio of carbon to hydrogen However we need to know the mass to determine the proper structure information about functional groups and carbon skeleton Mass is provided by mass spectrometry Functional groups provided by infrared spectroscopy Carbon skeleton provided by NMR spectroscopy In mass spectrometry a sample is heated and the vapors are hit with electrons creating a cation The cation will travel to a negatively charged accelerator plate It will then enter a curved magnet deflecting it from a straight path You can choose the mass of particles will that pass through the magnets to a detector plate This gives a ratio of mass to charge m z the highest peak relative to m z axis is the cation molecular ion The other lines provided are fragmentation ions The molecular ion needs highest m z not the highest intensity Mass spectrometer detects only charged particles From this we can determine a molecular mass b prescence of N will tell you only if you have an odd number of N These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute c presence of Br or Cl these are mixtures of two odd numbered masses Br 79 or 81 Cl 35 or 37 Br is in a 1 1 ratio whereas Cl is a 3 1 ratio between M and M 2 Mass spectrometry cannot tell difference between structure or where functional groups are II Electromagnetic Spectrum E hv h c Gamma rays 10 16 10 18m xrays 10 11 10 8 UV 10 9 10 7 visible 300700nm infrared 10 6 10 3 microwave 10 3 10 1 radiowave 1 100m Nm 10 9m Gamma rays and xrays are destructive UV induce a change in e transition Infrared vibrates molecules along their bonds Microwaves induce rotation Radiowaves change the spin of e III Infrared spectroscopy Infrared light 2500 25000nm 400 4000 1 cm Water glass and snow absorb infrared light so NaCl is used for the lens V a k 1 2 reduced mass m1m2 m1 m2 V C O 1100 V C O 1700 V C H 3000 V C C 1200 V C D 2100 From infrared spectroscopy we gain a graph of v vs transmittance No two molecules have the same fingerprint region We have to analyze by comparison to computer database R2C 0 1630 1820 R2C CR2 1600 1800 moderate to weak OH 3200 3650 NH2 3100 3550 CH SP3 2800 3000 SP2 3000 3100 SP 3300 H C O 2700

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