Chapter 6: Alkyl Halides


Homework:  1-3, 8-10, 13-15, 17-19, 21-23, 25, 27, 30, 36, 40, 44, 45, 53, 54 and 64.

Goal:  To understand the types of reactions which alkyl halides undergo.  You will learn the differences between substitution and elimination reactions.  You will be able to predict the products of these reactions.

Lecture Outline 10/14/97
             Reading:  Sections 1-6

A.  Types of Alkyl halides - be able to differentiate among alkyl, vinyl and aromatic halides.
B.  Nomenclature of Alkyl Halides - we have seen many of these compounds in the previous chapter.  Read this section and practice nomenclature with problem 2.
C.  Properties of Alkyl Halides - polarity of bond and density.
D.  Preparation of Alkyl Halides 
        1.  Free-radical halogenation
        2.  Allylic halogenation 
                a.  stability of allylic radical
                b.  bromination with NBS

Lecture Outline 10/17/97
             Reading:  Sections 7-12 

E.  Reactions of Alkyl Halides - Substitution and Elimination Reactions
        1.  Sn2 Reactions -concerted reactions of a nucleophile with an electrophile (alkyl halide)
                a.  Rate - dependent on the concentrations of both the nucleophile and electrophile
                b.  Nucleophile - relative strengths of nucleophiles
                c.  Substrate (alkyl halide) - 1° and some 2° alkyl halides
                        1)  leaving group ability
                        2)  steric interactions
                d.  Stereochemistry - always inverts the configuration

Lecture Outline 10/20/97
                Reading:  Section 13-16

        2.  Sn1 Reactions - stepwise reaction of a nucleophile and an electrophile
                a.  Rate - dependent only on the concentration of the electrophile 
                b. Substrate - 3° and some 2° alkyl halides
                        1)  substituent effects
                        2)  leaving group ability
                c.  Stereochemistry - racemize product (equal amounts of both enantiomer)
                d.  Rearrangements

Lecture Outline 10/22/97
                Reading:  Section 17-19

        3.  E1 Reactions - elimination reaction of a halide providing an alkene
                a.  Rate - dependent on the concentration of the electrophile
                b.  Mechanism - carbocation intermediate, competes with Sn1
        4.  E2 Reactions - elimination reaction generating an alkene
                a.  Rate - depends on concentration of both nucleophile and electrophile
                b.  Orientation - Saytzeff's rule  "Always form the most highly substituted double bond
 
Lecture Outline 10/24/97
                Reading:  Sections 20-22

               c.  Stereochemistry
                        1) Diastereomers give different geometric isomers (cis/trans)
                        2) Cyclohexanes must assume an anti-periplanar conormation for elimination.
        5.  Comparing and contrasting Sn1, Sn2, E1 and E2 reactions