Chapter 6 - 1 Classes of Halides Alkyl Halogen X is...

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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. Examples: 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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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. => C H H H Br δ+ δ- Nu + Nu C H H H Br +
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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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5 Classify These: CH 3 CH CH 3 Cl CH 3 CH 2 F (CH 3 ) 3 CBr CH 3 I =>
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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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7 IUPAC Nomenclature Name as haloalkane. 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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8 “Trivial” 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 CHCl 3 is chloroform CCl 4 is carbon tetrachloride. =>
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9 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 ozone layer. Pesticides - DDT banned in U.S. =>
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10 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 1.56 D 1.51 D 1.48 D 1.29 D Molecular dipoles depend on shape , too! x =>
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Boiling Points Greater intermolecular forces, higher b.p. dipole-dipole attractions not significantly different for different halides London forces greater for larger atoms Greater mass, higher b.p. Spherical shape decreases b.p.
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This note was uploaded on 01/12/2009 for the course CHE 201 taught by Professor Bong during the Fall '08 term at SUNY Buffalo.

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Chapter 6 - 1 Classes of Halides Alkyl Halogen X is...

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