CHEM301 F10 CA9A key

CHEM301 F10 CA9A key - CHEM301, Fall 2010 Dr. Ruder 1 Class...

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CHEM301, Fall 2010 Dr. Ruder 1 Class Activity 9A Substitution Nucleophilic Bimolecular, SN2 One-step nucleophilic substitution. Model 1 : Nucleophilic Substitution Reactions In a substitution reaction, an incoming group replaces another group referred to as the leaving group. Two examples of substitution reactions are shown below. Br H H H I + I H H H + Br H O O H H H S O O CH 3 HO H H H O S O O CH 3 + + incoming group incoming group leaving group leaving group δ + δ + δ - δ - Questions 1. For each reaction in Model 1: (a). Identify the incoming group (on the reactants side) by drawing a box around it. See above. (b). Circle the leaving group (on the reactants side). (c). Can incoming groups and leaving groups contain more than one atom? (d). Provide an explanation for why these reactions are called substitution reactions. One group replaces or is substituted for another. An incoming group replaces a leaving group. 2. Add a δ + and δ - on the compounds that contain the leaving group to indicate which way the C- leaving group bond is polarized. See above. 3. Use curved arrows to illustrate the mechanism that will accomplish each substitution reaction shown in Model 1. (Remember that curved arrows show electron movement.) See above. 4. For the following questions remember that “phile ” means “lover of”: (a). What is the charge of a nucleus, (circle one) + or - ? (b). A nucleophile is attracted to another atom with what charge, (circle one) + or –? (c). A nucleophile has electrons to (circle one) donate / accept . Based on this answer, would a nucleophile be considered a Lewis Acid or a Lewis Base ? (d). For the two reactions in Model 1, identify the nucleophile in each reaction. The incoming group is the nucleophile in both cases. (e). An electrophile is an atom that is attracted to another atom with (circle one) + or charge? (f). An electrophile has electrons to (circle one) donate / accept . Based on this answer, would an electrophile be considered a Lewis Acid or a Lewis Base? (g). For the two reactions in Model 1, identify the atom that is acting as the electrophile. The carbon that is labeled d+ is the electrophile.
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CHEM301, Fall 2010 Dr. Ruder 2 Model 2: One-Step Nucleophilic Substitution (SN2) The mechanism for an SN2 reaction is shown below. The transition state is the highest potential energy species between the reactant and the product. Nu- E+ Br H H H I + I H H H + Br Br I H H H transition state Questions 5. For the reaction shown in Model 2: (a). How many reactants are involved in the reaction? two (b). Label the nucleophile (Nu-) and electrophile (E+), and circle the leaving group. (c). What bond is being formed in this reaction? _ I-C __ What bond is being broken? _ C-Br __ (d). Draw curved arrows to show electron movement. See above. 6.
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CHEM301 F10 CA9A key - CHEM301, Fall 2010 Dr. Ruder 1 Class...

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