Chem241a_Lecture_13 - Or ganic Chemistry 241a Prof. Bogdan...

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Unformatted text preview: Or ganic Chemistry 241a Prof. Bogdan Olenyuk Contact Information Office: Old Chemistry 309 olenyuk@email.arizona.edu Phone: (520) 626-0754 Course web site: http://www.chem.arizona.edu/courseweb/074/CHEM241A1_2/FrameSet.html Chapter 5: Reactions and Mechanisms Organic mechanisms Today we will cover: Reading Assignment: McMurry (the BOOK), Ch. 5.1-5.1 1 Generalized Polar Reactions A n electrophile , an electron-poor species, combines with a nucleophile , an electron-rich species An electrophile is a Lewis acid A nucleophile is a Lewis base The combination is indicate with a curved arrow from nucleophile to electrophile An Example of a Polar Reaction: Addition of HBr to Ethylene HBr adds to the part of C-C double bond T h e bond is electron-rich, allowing it to function as a nucleophile H-Br is electron deficient at the H since Br is much more electronegative, making HBr an electrophile Mechanism of Addition of HBr to Ethylene HBr electrophile is attacked by electrons of ethylene (nucleophile) to form a carbocation intermediate and bromide ion Bromide adds to the positive center of the carbocation , which is an electrophile, forming a C-Br bond The result is that ethylene and HBr combine to form bromoethane All polar reactions occur by combination of an electron- rich site of a nucleophile and an electron-deficient site of an electrophile Using Curved Arrows in Polar Reaction Mechanisms Curved arrows are a way to keep track of changes in bonding in polar reaction...
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This note was uploaded on 08/23/2008 for the course CHEM 241A taught by Professor Olenyuk during the Fall '07 term at University of Arizona- Tucson.

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Chem241a_Lecture_13 - Or ganic Chemistry 241a Prof. Bogdan...

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