lectures 5-6 sp 09 preview

lectures 5-6 sp 09 preview - Lecture 5 Chemistry 310N...

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Unformatted text preview: Lecture 5 Chemistry 310N Chemistry 310N Organic Chemistry II for Prehealth Professionals Unique number: 53185 Tu,Th 12:30-2:00 pm, Welch 2.224 Professor: Jonathan Sessler, Ph.D. sessler@mail.utexas.edu Guest Lecturer: Dr. Brett Rambo, Ph.D. Notes: Dr. Sessler is out of town today. He will be back Thursday for class. Dr. Rambo will hold office hours from 2-4 pm in Dr. Sesslers office 13 C NMR spectroscopy, although in the book, will not be on Exam I Chemical Shift - 1 H-NMR Average values of chemical shifts of representative types of hydrogens. Chemical Chemical Shifts Shifts H-NMR H-NMR RC H 2 OR ( C H 3 ) 4 Si ArC H 3 RC H 3 RC C H RCC H 3 RO H RC H 2 OH ArC H 2 R O O RC H 2 R R 3 C H R 2 N H RCC H 2 R R 2 C= CRC H R 2 R 2 C= C H R RC H O RCO H O RC H 2 Cl RC H 2 Br RC H 2 I RC H 2 F Ar H O O R 2 C= C H 2 RCOC H 3 RCOC H 2 R ArO H 9.5-10.1 3.7-3.9 3.4-3.6 Type of Hydrogen 0 (by definition) Type of Hydrogen Chemical Shift ( 29 1.6-2.6 2.0-3.0 0.8-1.0 1.2-1.4 1.4-1.7 2.1-2.3 0.5-6.0 2.2-2.6 3.4-4.0 (29 3.3-4.0 2.2-2.5 2.3-2.8 0.5-5.0 4.6-5.0 5.0-5.7 10-13 4.1-4.7 3.1-3.3 3.6-3.8 4.4-4.5 6.5-8.5 4.5-4.7 Chemical Shift Chemical shift depends on the (1) electronegativity of nearby atoms, (2) hybridization of adjacent atoms, and (3) diamagnetic effects from adjacent pi bonds. Electronegativity C H 3 OH C H 3 F C H 3 Cl C H 3 Br C H 3 I (C H 3 ) 4 C (C H 3 ) 4 Si CH 3-X Electroneg- ativity of X Chemical Shift ( 29 4.0 3.5 3.1 2.8 2.5 2.1 1.8 4.26 3.47 3.05 2.68 2.16 0.86 0.00 Chemical Shift Hybridization of adjacent atoms. RC H 3 , R 2 C H 2 , R 3 C H R 2 C=C H R, R 2 C=C H 2 RC H O R 2 C=C(R)C H R 2 RC C H Allylic Type of Hydrogen (R = alkyl) Name of Hydrogen Chemical Shift ( 29 0.8 -1.7 1.6 -2.6 4.6 -5.7 9.5-10.1 2.0 -3.0 Chemical Shift Diamagnetic effects of pi bonds A carbon-carbon triple bond shields an acetylenic hydrogen and shifts its signal to lower frequency (to the right) to a smaller value. A carbon-carbon double bond deshields vinylic hydrogens and shifts their signal to higher frequency (to the left) to a larger value. RC H 3 R 2 C=C H 2 RC C H Type of H Name Alkyl Vinylic Acetylenic 0.8- 1.0 4.6 - 5.7 2.0 - 3.0 Chemical Shift ( 29 Chemical Shift Magnetic induction in the bonds of a carbon-carbon triple bond shields an acetylenic hydrogen and shifts its signal lower frequency. Chemical Shift Magnetic induction in the bond of a carbon-carbon double bond deshields vinylic hydrogens and shifts their signal higher frequency. Chemical Shift The magnetic field induced by circulation of electrons in an aromatic ring deshields the hydrogens of the aromatic ring and shifts their signal to higher frequency. This will become more clear as we work through some examples....
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lectures 5-6 sp 09 preview - Lecture 5 Chemistry 310N...

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