lecture 8 - Structure Haloalkanes, RadicalReactions Chapter...

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1 Haloalkanes Haloalkanes , RadicalReactions RadicalReactions Chapter 8 Chapter 8 Structure Structure ± Haloalkane (alkyl halide): a compound containing a halogen covalently bonded to an sp 3 hybridized carbon; given the symbol RX ± Haloalkene (vinylic halide): a compound containing a halogen bonded to an sp 2 hybridized carbon ± Haloarene (aryl halide): Haloarene (aryl halide): a compound containing a halogen bonded to a benzene ring; given the symbol ArX (we do not study vinylic or aryl halides in this chapter) Nomenclature Nomenclature number the parent chain to give the substituent encountered first the lowest number, whether it is a halogen or an alkyl group indicate halogen substituents by the prefixes fluoro-, chloro-, bromo-, and iodo-, and list them in alphabetical order with other substituents Nomenclature locate each halogen on the parent chain by giving it a number preceding the name of the halogen in haloalkenes, number the parent chain to give carbon atoms of the double bond the lower set of numbers Nomenclature Nomenclature examples Br 2-Bromo-4-methyl- pentane 1 2 3 4 5 4-Bromo- cyclohexene 1 2 3 4 5 6 trans -2-Chloro- cyclohexanol Br Cl OH
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2 Nomenclature Nomenclature ± Common names: Common names: name the alkyl group followed by the name of the halide Br Cl 2-Bromobutane ( sec -Butyl bromide Cnhloroethene (Vinyl chloride) 3-Chloropropene (Allyl chloride) Nomenclature Nomenclature several polyhaloalkanes are common solvents and are generally referred to by their common or trivial names CHCl 3 CH 2 2 Dichloromethane (Methylene chloride) Trichloromethane (Chloroform) CCl 2 =CHCl 3 3 Trichloroethyne (Trichlor) 1,1,1-Trichloroethane (Methyl chloroform) Nomenclature hydrocarbons in which all hydrogens are replaced by halogens are commonly named as perhaloalkanes or perhaloalkenes Perchloroethylene Perfluoropropane Perchloroethane CC FCCCF F F F F F F IUPAC practice Dipole Moments ± Dipole moment of RX depends on: the sizes of the partial charges the distance between them the polarizability of the unshared electrons on halogen 3 3 F 3 3 I Halomethane Electronegativity of Halogen Carbon-Halogen Bond Length (pm) Dipole Moment (debyes; D) 4.0 3.0 2.8 2.5 139 178 193 214 1.85 1.87 1.81 1.62 van der Waals Forces van der Waals Forces ± Haloalkanes are associated in the liquid state by van der Waals forces ± van der Waals forces: van der Waals forces: a group intermolecular attractive forces including dipole-dipole forces dipole-induced dipole forces induced dipole-induced dipole (dispersion) forces
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3 van der Waals Forces van der Waals Forces ± van der Waals forces pull molecules together as molecules are brought closer and closer, van der Waals attractive forces are overcome by repulsive forces between electron clouds of adjacent atoms or molecules van der Waals Forces van der Waals Forces the energy minimum is where the attractive forces are the strongest nonbonded interatomic and intermolecular distances at these minima can be measured by x-ray
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This note was uploaded on 09/06/2009 for the course CHEM chem 12 AB taught by Professor Valentin during the Spring '09 term at Evergreen Valley.

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lecture 8 - Structure Haloalkanes, RadicalReactions Chapter...

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