CH238_Study_Guide_Fall_2009[1]

CH238_Study_Guide_Fall_2009[1] - CH 238 Final Exam Study...

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CH 238 Final Exam Study Guide FRIEDELCRAFTS REACTION: What is an Electrophile? Any positive species that can accept electrons. In this case, t-butyl alcohol lost the alcohol to become a tertiary carbocation. That was the electrophile. Method and Mechanisms of forming Alkyl Electrophiles Mechanism for Electrophilic Aromatic Substitution. Steric and Electronic Effects (ortho, para or meta directing effects) of substituents on Electrophilic Aromatic Substitution. Electron donating groups are ortho-para. Electron withdrawing groups are meta. Examples. . NITRATION OF METHYL BENZOATE: Mechanism of formation of Nitronium ion . Role of Sulfuric acid. Sulfuric acid donates a H+ to nitric acid. It helps generate the electrophile, the nitronium ion. Effect of temperature on nitration products.
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The maintenance of cold temperature (5-20 degrees) is important as it allows just enough energy to generate a meta-sub product and no other orientations. If temperature > 20 degrees, the there will be EXCESS energy in the system to create more nitro-sub’d products that desired (i.e. ortho-para is possible). If temperature < 5 degrees, then there will NOT be enough energy to create the desired nitro-sub’d product. Mechanism for Electrophilic Aromatic Substitution. Refer to Page 1. Friedel Crafts. Steric and Electronic Effects (ortho, para or meta directing effects) of substituents on Electrophilic Aromatic Substitution. Refer to Page 1. Friedel Crafts. SODIUM BOROHYDRIDE REDUCTION OF BENZIL: Reaction of Aldehydes or Ketones with Sodium Borohydride and its Mechanism. Application of Mechanism to Benzil and Stereochemistry involved. THE GRIGNARD REACTION: Formation of Grignard Reagent (What is different about it? Function as a carbon nucleophile)
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Grignard reagent is a carbon anion that can act as a nucleophile. Why are the reaction conditions to be maintained anhydrous? Different methods to assist in the formation of the Grignard Reagent. 1. Crushing the Mg turnings carefully with a glass stirring rod 2. Warming up the flask 3. Adding tiny crystals of iodine to the flask (not used in our experiment) Mechanism for Grignard Reaction and its application. Use of Hydrochloric acid during isolation of the product. As shown in above mechanism, H+ is needed for work up to get rid of MgX from O - . ALDEHYDES AND KETONES: Qualitative Tests for Aldehydes and Methyl Ketones. Tollens’ Test uses a weak oxidizing agent thus giving a POSITIVE reading for ALDEHYDES and not ketones.
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Iodoform Test reads positive for METHYL KETONES. Iodoform Test is more reliable than Tollens’. Structural difference between Methyl ketones and other ketones and the test to distinguish between the two. Methyl ketones have a methyl on a ketone; whereas, other ketones may not. You may run an iodoform test. If iodoform test is positive, then you have a methyl ketone. Mechanism for the formation of an imine (Reaction of an aldehyde or ketone with any generic amine) and
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CH238_Study_Guide_Fall_2009[1] - CH 238 Final Exam Study...

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