Chapter06notes

Chapter06notes - 1. Alkyl Halides CX Bond Lengt h ( ) 1.39...

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1 1. Alkyl Halides C–X Bond Length (Å) 1.39 1.78 1.93 2.14 C–X Bond Strength (kJ/mol) 472 350 293 239 increase decrease
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2 1. Types of Alkyl Halides
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3 Alkyl halides are weakly polar molecules. They exhibit dipole-dipole interactions because of their polar C-X bond. Since the rest of the molecule contains only C-C and C-H bonds, they are incapable of intermolecular hydrogen bonding. 1. Polarity of Alkyl Halides
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4 1. Physical Properties of Alkyl Halides Boiling Point (bp/oC) C h l o r i d e -23.8 13.1 78.4 68 69 51 G r o u p Me Et Bu s Bu i Bu t Bu F l u o r i d e -78.4 -37.7 32 - - 12 B r o m i d e 3.6 38.4 101 91.2 91 73.3 I o d i d e 42.5 72 130 120 119 100(dec)
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5 1. Physical Properties of Alkyl Halides Density ( ρ ) C h l o r i d e 0.92 0.91(15) 0.89 0.87 0.87 0.84 G r o u p Me Et Bu s Bu i Bu t Bu F l u o r i d e 0.84(-60) 0.72 0.78 - - 0.75(12) B r o m i d e 1.73(0) 1.46 1.27 1.26 1.26 1.22 I o d i d e 2.28 1.95 1.61 1.60 1.60 1.57(0)
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6 1. Common Alkyl Halides
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7 2. Reaction Types for Alkyl Halides
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8 But what is the order of bond making and bond breaking? Two mechanisms: Bond making and breaking occur at the same time. Bond breaking occurs first. 2. Bond Breaking and Making in Nucleophilic Substitution Mechanisms
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9 Three components are necessary in any substitution reaction. 2. Substitution Reactions
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10 Nucleophiles are Lewis bases that can be negatively charged or neutral. Negatively charged nucleophiles like HO¯ and HS¯ are used as salts with Li+, Na+, or K+ counterions to balance the charge. Since the identity of the counterion is usually inconsequential, it is often omitted from the chemical equation. 3. Nucleophiles in Substitution Reactions
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11 When a neutral nucleophile is used, the substitution product bears a positive charge. 3. Neutral Nucleophiles The substitution product’s positive charge is usually caused by a proton bonded to O or N. That proton is readily lost from this in a BrØnsted-Lowry acid-base reaction, forming a neutral product.
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12 3. Common Nucleophiles
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13 In a nucleophilic substitution reaction of R-X, the C-X bond is heterolytically cleaved, and the leaving group departs with the electron pair in that bond, forming X: ¯ . The more stable the leaving group X: ¯ , the better able it is to accept an electron pair. For example, H2O is a better leaving group than HO ¯ because H2O is a weaker base. 3. The Leaving Group
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14 The overall effect of any nucleophilic substitution is the replacement of the leaving group by the nucleophile. To draw any nucleophilic substitution product: Find the sp 3 hybridized carbon with the leaving group. Identify the nucleophile, the species with a lone pair or  bond. Substitute
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This note was uploaded on 11/09/2011 for the course CHEM 2341 taught by Professor Staff during the Fall '11 term at Texas State.

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Chapter06notes - 1. Alkyl Halides CX Bond Lengt h ( ) 1.39...

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