CH6 - Chapter 6 Alkyl Halides: Nucleophilic Substitution...

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Unformatted text preview: Chapter 6 Alkyl Halides: Nucleophilic Substitution and Elimination 6-1 Introduction Alkyl Halide: Halogen atom bonded to one of the sp 3 hybrid carbon atoms of an alkyl group Vinyl Halide: Halogen atom bonded to one of the sp 2 hybrid carbon atoms of an alkene Aryl halide: halogen bonded to one of the sp 2 hybrid carbon of an aromatic ring Carbon halogen bond is polar because halogen atoms are more electronegative than carbon atoms. Most reactions breaking this polarized bond Halogen can be eliminated or substituted- this versatility allows alkyl halides to serve as intermediates in the synthesis of many other functional groups 6-2 Nomenclature of Alkyl Halides IUPAC or common names Common names- name alkyl group then halide (p273) CH 2 X 2 (methylene group with 2 halogens) methylene halide CHX 3 (haloform) CX 4 (carbon tetrahalide) Primary Halide (1) Halogen bearing carbon bonded to one other carbon Secondary Halide (2) Halogen bearing carbon bonded to two other carbons Tertiary Halide (3) Halogen bearing carbon bonded to three other carbons Geminal Dihalide: Two halogen atoms bonded to the same carbon Vicinal Dihalide: To halogens bonded to adjacent carbons 6-3 Common Uses of Alkyl Halides 6-3A Solvents Industrial and household solvents, cleaning degreasing Potentially toxic and carcinogenic 6-3B Reagents Use as starting materials for making more complex molecules 6-3C-Anesthetics (CHCl 3 ) first substance for general anesthetics Halothane- safer 6-3D Refrigerants and Foaming Agents Freons (Chlorofluorocarbons) Used to cool down Foam- harden plastics CFCs gradually diffuse into ozone. Deplete the ozone layer HCFCs are destroyed at lower altitude 6-3E Pesticides DDT- prevented death of malaria An ounce will kill a human but that same amount will protect an acre of land 6-4 Structure of Alkyl Halides Halogen atom is bonded to an sp 3 hybrid carbon atom Halogen is more electronegative than carbon, and the C X bond is polarized with a partial positive charge on carbon and partial negative charge on the halogen = 4.8 x x d equals charge and d is bond length dipole moment Electronegativities of halogens increase in order Smaller halogens have greater electronegativities I < Br < Cl < F Carbon Halogen bond lengths increase as the halogen atoms become bigger *larger halogens have larger bonds Bond length: C F < C Cl < C F < C I Two effects oppose each other. Bond Dipole moments increase in order (D) C I < C Br < C F < C Cl Molecular dipole- vector sum of individual dipole moments 6-5A Boiling Points London Force- Strongest intermolecular attraction in alkyl halides Surface attractions from coordinated temporary dipoles Larger Surface area larger London attractions higher boiling points Dipole Dipole attractions ( from polar C X ) bond affect boiling point (but not as much) Molecules with higher molecular weights generally have higher boiling points 6-5B Densities...
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This note was uploaded on 05/08/2008 for the course CHE 1120 taught by Professor Brown during the Spring '08 term at St. Johns Duplicate.

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CH6 - Chapter 6 Alkyl Halides: Nucleophilic Substitution...

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