Alkyl Halides Dr. Noha Elnagdi

Introduction (just read) Organic halogen compounds are very common and important classes of organic molecules. Many organic halides occur in nature and others are produced in the laboratory. Thyroxine, a thyroid hormone, is an aryl iodide. Alkyl halides are nonflammable and nonpolar. These properties have made them useful as solvents for dry cleaning and degreasing applications. However, the toxicity of these compounds has led to substitutes for most of these applications. Even though chlorofluorocarbons are nonflammable, nontoxic and have mechanical properties that make them good refrigerants in air conditioners and refrigerators, the stability of these compounds in the troposphere and their ability to break down stratospheric ozone have led to a ban on these compounds. Chlorinated organic compounds have been widely used as pesticides. The discovery of the insecticidal properties of DDT in 1939 led to the development of the pesticide industries. The general anesthetic halothane is used instead of toxic agents like chloroform or flammable compounds like ether.

IUPAC Nomenclature Haloalkane (one word)

Common Nomenclature Alkyl + Halide

CH3F CH3CH2CH2CH2CH2Cl Methyl fluoride Pentyl chloride CH3CH2CHCH2CH2CH3 Br Cyclohexyl iodide hexyl bromide

1) Classes of alkyl halides Depending on the type of carbon to which the halogen is attached 1o alkyl halides 2o alkyl halides 3o alkyl halides

A halogen attached to a carbon next to a doubly bonded carbon is an Allylic Halide

A halogen is attached directly to a doubly bonded carbon is called: Vinylic halides

A halogen one carbon away from an aromatic ring is Benzylic Halide

A halogen attached directly to a benzene ring is an Aryl halide

Physical Properties of Organic Halides All organic halides are insoluble in water and soluble in common organic solvents. The boiling points increases with increasing in molecular weights. Therefore, the boiling points increases in the order RF< RCl< RBr< RI. See Videos: 1

Preparation of Halogen Compounds a- Halogenation of alkanes (video) b- Halogenation of alkenes (Video)

c- Halogenation of alkynes

d- Halogenation of alkyl benzenes and aromatic ring

2- Conversion of alcohols

Reactions of Organic Halides 1- Nucleophilic Subtitution Reactions Nu= OH, OR, OCOR, NH2, RNH, SH, SR, RC=C, CN, X’

3- Reaction of Grignared reagent a- Formation of Grignard reagent b- Reaction of Grignard reagent

4- Reduction of alkyl halides a- Reduction by metal and acid b- From coupling with metal c- Using Gilman reagent