Chapter 3 Slides- Solomons and Fryhle

Chapter 3 Slides- Solomons and Fryhle - Chapter3...

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Chapter 3 An Introduction to Organic Reactions: Acids and Bases
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Reactions and Their Mechanisms There are four general types of organic reactions: Substitutions Additions Eliminations
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Rearrangements Cleavage of Covalent Bonds g Homolysis Heterolysis y
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In Class Problem: Designate each of the following reactions as (a) a substitution, (b) an elimination, (c) an addition, (d) a rearrangement, or (e) some combination of the former. CH 2 Cl CH 2 CN + CN - + Cl - (1) CC CH 3 CH 2 H 3 C H 2 C + 2H 2 CH CH CH 3 CH 3 H 3 C H 3 C (2) + HNO 3 H 2 SO 4 NO 2 + H 2 O (3) H 3 CH 3 C CH 3 CH 3 H 2 SO 4 H 3 CH 3 CH 3 + H 2 O (4) OH OH O CH
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Heterolytic reactions almost always occur at polar bonds. The reaction is often assisted by formation of a new bond to another molecule. The following two examples illustrate two types of heterolytic cleavage reactions: (1) An example of a unimolecular reaction process:
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(2) An example of a bimolecular reaction process:
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Introduction to Acid Base Chemistry Brønsted Lowry Definition of Acids and Bases Acid: a substance that can donate a proton. Base: a substance that can accept a proton. ample: ydrogen chloride is a very strong acid. When dissolved in water Example: Hydrogen chloride is a very strong acid. When dissolved in water essentially all hydrogen chloride molecules transfer their proton to water. ample: queous hydrogen chloride and aqueous sodium hydroxide are mixed. Example: Aqueous hydrogen chloride and aqueous sodium hydroxide are mixed. The actual reaction is between hydronium and hydroxide ions.
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Lewis Definition of Acids and Bases Lewis Acid: electron pair acceptor wis Base: ectron pair donor Lewis Base: electron pair donor (Curved arrows show movement of electrons to form and break bonds.) Opposite Charges Attract and React BF 3 and NH 3 react based on their relative electron densities. BF 3 has substantial positive charge on the boron. NH 3 has substantial negative charge localized at the lone pair on nitrogen. p g
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In Class Problem: Write an equation that shows the Lewis acid and Lewis base in the reaction of (a) molecular chlorine (Cl 2 ) with aluminum chloride (AlCl 3 ). ) oron ifluoride F with rt utyl alcohol ((CH OH) (b) boron trifluoride (BF 3 ) with tert butyl alcohol ((CH 3 ) 3 COH).
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Heterolysis of Bonds to Carbons: Carbanions and Carbocations Reaction can occur to give a carbocation or carbanion depending on the nature of Z. Carbocations (Lewis acids) have only 6 valence electrons and a positive charge. Carbanions (Lewis bases) have 8 valence electrons and a negative charge. ( ) g g
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Organic Chemistry Terms for Lewis Acids and Bases Electrophiles (“electron loving” reagents ): seek electrons to obtain a stable valence shell of electrons. They are electron deficient species e.g. carbocations. Nucleophiles (“nucleus loving” reagents): seek a proton or some other positively charged center. They are electron rich species e.g. carbanions.
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Chapter 3 Slides- Solomons and Fryhle - Chapter3...

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