Chapter 6 - Introduction to General and Organic Chemistry...

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Chapter 6 Alkyl Halides: Nucleophilic Substitution and Elimination Dr. David P. Brown Department of Chemistry Introduction to General and Organic Chemistry II
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Chapter 6 2 Classes of Halides Alkyl : Halogen, X, is directly bonded to sp 3 carbon. Vinyl : X is bonded to sp 2 carbon of alkene. Aryl : X is bonded to sp 2 carbon on benzene ring. C H H H C H H Br alkyl halide C C H H H Cl vinyl halide I aryl halide
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Chapter 6 3 Polarity and Reactivity Halogens are more electronegative than C. Carbon-halogen bond is polar, so carbon has partial positive charge. Carbon can be attacked by a nucleophile. Halogen can leave with the electron pair.
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Chapter 6 4 Classes of Alkyl Halides • Methyl halides : only one C, CH 3 X Primary : C to which X is bonded has only one C-C bond. Secondary : C to which X is bonded has two C-C bonds. Tertiary : C to which X is bonded has three C-C bonds.
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Chapter 6 5 Examples: CH 3 CH CH 3 Cl CH 3 CH 2 F (CH 3 ) 3 CBr Br 2 1 3 2
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Chapter 6 6 Dihalides Geminal dihalide : two halogen atoms are bonded to the same carbon Vicinal dihalide : two halogen atoms are bonded to adjacent carbons. C H H H C H Br Br geminal dihalide C H H Br C H H Br vicinal dihalide
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Chapter 6 7 IUPAC Nomenclature Named as haloalkanes . Choose the longest carbon chain, even if the halogen is not bonded to any of those C’s. Use lowest possible numbers for position. CH 3 CH CH 2 CH 3 Cl CH 3 (CH 2 ) 2 CH(CH 2 ) 2 CH 3 CH 2 CH 2 Br 2-chlorobutane 4-(2-bromoethyl)heptane
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Chapter 6 8 Systematic Common Names Name as alkyl halide . Useful only for small alkyl groups. Examples: CH 3 CH CH 2 CH 3 Cl CH 3 CH CH 3 CH 2 F sec -Butyl chloride Isobutyl fluoride
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Chapter 6 9 Common Names CH 2 X 2 called methylene halide. CHX 3 is a haloform. CX 4 is carbon tetrahalide. Examples: CH 2 Cl 2 is methylene chloride
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Chapter 6 10 Uses of Alkyl Halides Solvents - degreasers and dry cleaning fluid Reagents for synthesis of other compounds Anesthetic : Halothane is CF 3 CHClBr CHCl 3 used originally (toxic and carcinogenic) Freons , chlorofluorocarbons or CFC’s Freon 12, CF 2 Cl 2 , now replaced with Freon 22, CF 2 CHCl, not as harmful to the ozone layer. Pesticides - DDT banned in the U.S .
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Chapter 6 11 Dipole Moments μ = 4.8 x δ x d , where δ is the charge (proportional to EN) and d is the distance (bond length) in Angstroms. Electronegativities: F > Cl > Br > I Bond lengths: C-F < C-Cl < C-Br < C-I Bond dipoles: C-Cl > C-F > C-Br > C-I Dipole moments 1.56 D 1.51 D 1.48 D 1.29 D Molecular dipoles depend on shape , too!
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Chapter 6 12 Boiling Points Greater intermolecular forces, higher b.p. Dipole-dipole attractions not significantly
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Chapter 6 - Introduction to General and Organic Chemistry...

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