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Lec-38-Chap-12-1 - Lewis Acids and Bases acid base => =>...

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1 Lecture 37 1 Lewis Acids and Bases • acid => electron pair acceptor • base => electron pair donor the base donates a pair of electrons to the acid forming a coordinate covalent bond Lecture 37 2 Lewis acids include: all Brønsted-Lowry acids molecules with vacant valence orbitals (BH 3 ) molecules with polar π bonds (CO 2 , RCO 2 H) metal cations Lewis bases include: all Brønsted-Lowry bases molecules with high energy filled orbitals such as – lone pairs (Brønsted-Lowry bases) π bonds
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2 Lecture 37 3 Lewis Acid and Base Reactions H + + NH 3 Ù ΝΗ 4 + acid base Cu +2 + 4 NH 3 Ù [Cu(NH 3 ) 4 +2 ] acid base Acid-Base Theories Arrhenius Acid-Base Theory : Acid: H + donor HF Base: OH donor NaOH Brønsted-Lowry Acid-Base Theory : Acid: H + donor HF Base: H + acceptor F Lewis Acid-Base Theory : Acid: e pair acceptor H + Base: e pair donor F Lewis acid-base theory extends the simplicity of acid-base chemistry to many other reactions.
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3 Avoid confusion!!! H + is the perfect acid in all theories Brønsted-Lowry – it gives of itself Lewis – it accepts electron pairs donor acceptor acid: H + e pair base: e pair H + Summary Common acids include binary acids, oxoacids, carboxylic acids, and hydrated metal ions Common bases include hydroxides, salts of weak acids, ammonia and amines Acid strength tends to increase with: Increasing electronegativity for binary acids in the same period Decreasing bond strength for binary acids in the same column Increasing numbers of oxygens for oxoacids Increasing electronegative substituents for carboxylic acids A Lewis acid is a lone pair acceptor; a Lewis base is a lone pair donor
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4 Lecture 38 & 39: Functional Groups of Organic Molecules; Introduction to Organic Reaction Mechanisms Moore et al Chapter 12.5-7 Review: 3.3-4, 8.11, 16.2 Questions for the Day: How can we understand the structures and properties of the enormous number of known organic molecules? How can we use Lewis acid-base theory to understand organic reactions? As the material on organic reactions is not in the text, be sure to use the following resources in learning this material: The link under workshops for Organic Reactions contains an additional discussion. Links to homework assignments are also provided Learning Objectives Know the names and formulas of the functional groups Know how each functional group can be created Use curved arrows to illustrate the mechanisms for: proton transfer substitution reactions addition-elimination reactions addition reactions elimination reactions Understand why particular atoms serve as Lewis acids and bases in these reactions Identify missing reagents or products associated with the above reactions
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5 Vocabulary Functional group Alkyl halide Alcohol Primary alcohol Secondary alcohol Tertiary alcohol Ether Aldehyde Ketone Carboxylic acid Ester Acid halide Amine Primary amine Secondary amine Tertiary amine Amide Substitution reaction Addition reaction Elimination reaction Addition-elimination reaction
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