2444-083111

2444-083111 - Everything is on-line http:

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Unformatted text preview: Everything is on-line http: //orgchem.chem.uconn.edu/courses/testhome.html old exams and quizzes syllabus all answer keys will be posted here To add the class - see me after class for a permission number Office: A-416 Phone: 486-2881 michael.smith@uconn.edu Office hours: 10-1, MWF THIS IS THIS IS NOT NOT ON HUSKY-CT ON HUSKY-CT When a molecule is placed in the mass spectrometer: Ejection of an electron gives a radical cation The molecular ion (parent ion) H 3 C O CH 3 H 3 C O CH 3 H 3 C O CH 3 + mass = 58 mass = 58 - 1e- Molecular ion or Parent ion 70 eV High energy Mass of acetone 1 e H 3 C O CH 3 H 3 C O CH 3 + mass = 58 mass = 58 - 1e- 70 eV H 3 C O CH 3 + + 1 2 3 mass = 43 mass = 15 Molecular ion fragments into daughter ions Ion Fragmentation: Daughter Ions m/z Abundance m 3 m 2 m 1 m=0 m=100 Separation of the ions, and detection leads to the mass spectrum Abundance is the amount of each ion detected, relative to the ion detected in greatest abundance (base ion = B) m/ z = mass/charge mass of each ion divided by the charge of that ion. If the charge is +1, then m/z= mass of the ion Mass Spectrum Mass spectrum for the ionization of acetone 10 20 30 40 50 60 70 m/z Relative Abundance H 3 C O CH 3 + H 3 C O + + CH 3 M 15 (loss of methyl) It is difficult to identify the ions a priori , but we can take the parent ion (M or P) and look for the mass of lost fragments. Loss of 15 mass units, for example, corresponds to loss of a methyl group from the parent. MS of Acetone 58 43 High Resolution Mass Spectrometry 5 Detection of radical cation fragments in modern mass spectrometers has been refined to the point where it is possible to determine the mass of a fragment to 4-5 decimal places. A molecular ion may be determined to 100.1251, or better. With this level of accuracy, a molecular formula may be obtained directly from the molecular ion. The values in the periodic table are the masses of the elements as found in Nature. However, carbon in Nature is not just carbon 12 ( 12 C), but a mixture of three isotopes, 12 C, 13 C, and 14 C. Since the mass spectrometer separates ions by mass, fragments containing different isotopes may be detected. High Resolution Mass Spectrometry 6 Isotopic abundance of common isotopes and Isotopic Masses 12 C 13 C 1 H 2 H 14 N 15 N 16 O 17 O 18 O 32 S 33 S 34 S 35 Cl 37 Cl 79 Br 81 Br I s o t o p e R e l a t i v e A b u n d a n c e ( % ) 100 1.1 100 0.106 100 0.38 100 0.14 0.20 100 0.78 4.40 100 32.5 100 98.0 I s o t o p e M a s s 12.00000 13.00336 1.00782 2.01410 14.00307 15.00010 15.99491 16.99913 17.99916 31.97207 32.9716 33.96786 34.96885 36.96590 78.91839 80.91642 High Resolution Mass Spectrometry 7 High resolution mass spectrometry provides a high level of accuracy for the molecular ion, but how is this translated to a formula?...
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2444-083111 - Everything is on-line http:

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