318-7 - Organic Lecture Series CH 318 N LECTURE 7 Textbook...

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Organic Lecture Series 1 CH 318 N LECTURE 7 Textbook Assignment: Chapter 14- Mass Spec Homework (for credit): POW 3 posted Today’s Topics: Mass Spec Cont’d Notice & Announcements: Next Class: “Name That Structure!!” Organic Lecture Series 2 M M ass ass S S pectrometry pectrometry
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Organic Lecture Series 3 A Mass Spectrometer A Mass Spectrometer A mass spectrometer is designed to do three things 1. convert neutral atoms or molecules into a beam of positive (or negative) ions 2. separate the ions on the basis of their mass-to-charge ( m/z ) ratio 3. measure the relative abundance of each ion Organic Lecture Series 4 Electron Ionization MS – in the ionization chamber, the sample is bombarded with a beam of high-energy electrons – collisions between these electrons and the sample result in loss of electrons from sample molecules and formation of positive ions + + + CH H H H C H H H e - 2e - H Molecular ion (a radical cation) A Mass Spectrometer A Mass Spectrometer
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Organic Lecture Series 5 Molecular ion (M): Molecular ion (M): a radical cation formed by removal of a single electron from a parent molecule in a mass spectrometer • It does not matter which electron is lost; radical cation character is delocalized throughout the molecule; therefore, write the molecular formula of the parent molecule in brackets with – a plus sign to show that it is a cation – a dot to show that it has an odd number of electrons Organic Lecture Series 6 –at times, however, it is useful to depict the radical cation at a certain position in order to better understand its reactions CH 3 2 OCH(CH 3 ) 2 . 3 2 3 ) 2 .
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Organic Lecture Series 7 Mass Spectrum Mass Spectrum Mass spectrum: Mass spectrum: a plot of the relative abundance of ions versus their mass-to- charge ratio Base peak: Base peak: the most abundant peak –assigned an arbitrary intensity of 100 •The relative abundance relative abundance of all other ions is reported as a % of abundance of the base peak Organic Lecture Series 8 MS of dopamine MS of dopamine – a partial MS of dopamine showing all peaks with intensity equal to or greater than 0.5% of base peak M-29
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Organic Lecture Series 9 Resolution Resolution: Resolution: a measure of how well a mass spectrometer separates ions of different mass – low resolution: low
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This note was uploaded on 03/23/2010 for the course CH 310n taught by Professor Iverson during the Spring '08 term at University of Texas at Austin.

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318-7 - Organic Lecture Series CH 318 N LECTURE 7 Textbook...

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