CHEM301 F08 CA6key

CHEM301 F08 CA6key - CHEM301, Fall 2008 Dr. Ruder 1 Class...

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CHEM301, Fall 2008 Dr. Ruder 1 Class Activity 6 Radical Halogenation Reactions Model 1: Heterolytic and Homolytic Bond Cleavage When compounds undergo reactions bonds are broken and new bonds are formed. Bond breakage can be described as heterolytic or homolytic as outlined below. X Y X + Y heterolytic X Y X + Y homolytic Questions 1. (a). Describe what happens to the electrons that make up the X-Y bond during heterolytic bond cleavage in Model 1. The pair of electrons in the sigma bond is transferred to one of the atoms making up the bond. (b). Explain what a full arrow (double barbed) illustrates. A full arrow depicts movement of a pair of electrons. 2. (a). Describe what happens to the electrons that make up the X-Y bond during homolytic bond cleavage in Model 1. A single electron is transferred to each of the atoms making up the original sigma bond. (b). Explain what a half arrow (single barbed) depicts. A half arrow depicts movement of one electron. 3. A radical species is a species that has an unpaired electron. Circle any radicals in Model 1. Model 2: Radical Bond Formation Homolytic bond cleavage results in formation of radical species. Once a radical species is formed, it can form a new bond by combining with another radical, or reacting with one electron of a sigma bond. X Y Z X Z Y + X Y X Y Questions 4. (a). Describe how the bond is forming in the top reaction of Model 2. Two electrons are combining, one from each radical species, to form a single bond. (b). Describe how the bond is forming in the bottom reaction of Model 2.
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CHEM301, Fall 2008 Dr. Ruder 2 Two electrons are combining, one from a radical species, and one from a sigma bond, to form another single bond. (c). The lower reaction shown in Model 2 is one of two sigma bond forming reactions that could have taken place with these two reactants. Use curved half arrows to show the mechanism of a reaction that yields Z-X and Y radical from these same reactants. X Y Z Y X Z + Model 3: Reaction of Bromine Radical With Alkanes The radical halogenation below illustrates the most likely radical products from reaction of bromine radical with various alkanes. C H Br H + Br H C H H H H C H C H H H H C H Br H + Br H C H H H C C H C H H C C CH 3 Br H + Br H C CH 3 H H H 3 C C CH 3 C CH 3 H H H 3 C H H H + H H H H + eq. a eq. b eq. c Questions 5. (a). Label the carbon radicals in Model 3 as methyl, primary, secondary or tertiary. C
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This note was uploaded on 02/17/2011 for the course CHEM 301 taught by Professor Sahli during the Fall '07 term at VCU.

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CHEM301 F08 CA6key - CHEM301, Fall 2008 Dr. Ruder 1 Class...

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