notes_14C_stereo01 - Stereochemistry A brief history…...

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Unformatted text preview: Stereochemistry A brief history… Christian Huygens discovered plane-polarized light in the late 17 th century. In 1815, Jean Baptiste Biot found that certain natural organic compounds, both liquids and solutions, rotate plane-polarized light. Carl Wilhelm Scheele made an important contribution to stereochemistry when studying the barrels and corks during grape juice fermentation. He discovered racemic acid in 1819 which had the identical structure (same chemical formula) of tartaric acid. Joesph Achille LeBel and Joobus Henricus van’t Hoff, in 1874, proposed carbon is tetrahedral and that a molecule possessing a tetrahedral carbon can exist as a pair of isomers. (source: Thinkbook 14-C; Hardinger; pgs 11-14) Cis-Trans Isomers (Bruice 4 th edition, 5.1) • A.K.A. geometric isomers o Cis isomer: hydrogens lie on same side of the double bond o Trans isomer: hydrogens lie on opposite sides of the double bond • Are a result of restriction rotation cause by a double bond or ring structure Non-Cyclic Example (Bruice ath edition, pg.183) H 3 C C H C CH 2 CH 3 H H 3 C C H C H CH 2 CH 3 cis-2-pentene trans-2-pentene Cyclic Example (Bruice 4 th edition, pg. 183) H Br H Cl Br H H Cl cis-1-bromo-3-chlorocyclobutane trans-1-bromo-3-chlorocyclobutane Chirality (Bruice 4 th edition, 5.2) • Chiral: object with a nonsuperimposable mirror image o Ex: hands, left hand looks like right hand in mirror; molecule with one asymmetric carbon • Achiral: object that has a superimposable image o any object that isn’t chiral o Ex: a spoon Asymmetric Carbons, Chirality Centers, and Stereocenters (Bruice 4 th edition, 5.3, 5.17, Hardinger Thinkbook 14C, pg.13) • Asymmetric carbon: a carbon with 4 different substituents o A.K.A Chirality Center (there are other types of chirality centers, see below) o the most usual cause of chirality in compounds o only sp3 hybridized carbons can be asymmetric carbons since sp and sp2 hybridized carbons can’t have four substituents • Chirality Centers o A type of stereocenter...
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This note was uploaded on 07/27/2009 for the course CHEM 14C-14D taught by Professor Hardinger during the Fall '08 term at UCLA.

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notes_14C_stereo01 - Stereochemistry A brief history…...

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