Chapter 3 Notes - 9/24/2010 Reactions and Their Mechanisms...

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9/24/2010 1 Chapter 3 Intro to Organic Reactions Acids and Bases 1 Substitutions ( b chpt. 6) Additions ( b chpt. 7) Eliminations ( b chpt. 7) Rearrangements Reactions and Their Mechanisms (3.1) 2 Cleavage of Covalent Bonds(3.1A) Homolysis (rare – needs weak bonds. Example: Cl 2 + light or peroxide bond cleavage with light) WHY are these weak? Heterolysis ( more common ) = 1 electron = 2 electrons 3 Brønstead-Lowry Acid-Base Reactions (3.2A) Brønstead-Lowry Acid: Substance that can donate (or lose) a proton (to give it’s conjugate base) Brønstead-Lowry Base: Substance that can accept (or gain) a proton (to give it’s conjugate acid) Strong acids will fully dissociate (give up proton) in water HCl, H 2 SO 4 (first proton), HBr, HI WHY? Why is HCl a strong acid? 4
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9/24/2010 2 Example A/B Reaction We add Na OH to a solution of H Cl (aq) The actual reaction is between hydronium and hydroxide ions 5 Lewis Acid/Base (more broad definition) Lewis Acid: Electron pair acceptor Lewis Base: Electron pair donor All Brønstead-Lowry A/B are Lewis A/B but not the other way around! Lewis A/B plays a big part in inorganic chemistry 6 Opposite Charges Attract and React Why does this reaction occur? 7 Electrophiles/Nucleophiles/LG Electrophiles (electron loving): Reagents which seek extra electrons Are often attacked by nucleophiles in chemical reactions Nucleophile (positive loving): Reagents which seek a positive center Often attack electrophiles (using an electron pair) in chemical reactions Leaving Group: A group which is capable of accepting an electron pair (by heterolytic bond cleavage) and leaving 8 Sir Christopher Kelk Ingold 1893-1970
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9/24/2010 3 Inductive Effects An effect felt through the sigma bond Can be electron withdrawing or electron donating Electron withdrawing (EW) inductive effects are caused by electronegative groups, or electron deficient groups, they PULL electron density to themselves Halogens often cause EW inductive effects Electron donating (ED) inductive effects are caused by electron donating groups (have a rich electron cloud), they PUSH electron density away from themselves Alkyl groups (carbon/hydrogen groups) are considered electron
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Chapter 3 Notes - 9/24/2010 Reactions and Their Mechanisms...

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