Organic Halogen Compounds Dr Nahed Elsayed 1

Learning Objectives Chapter five discusses the following topics and by the end of this chapter the students will: Recognize the structure and classes of organic halogen compounds Recognize the structure and classes of alkyl halides Know the common names and understand the IUPAC rules for nomenclature of halo compounds Understand the physical properties of halo compounds (solubility and boiling points) Know the different methods used in preparation of halo compounds Know the reactions of halo compounds; nucleophilic substitution, elimination, reduction reactions of Grignard reagents and know the previously discussed methods of reducing alkyl halides (Chapter-1)

Classes of organic halogen compounds They are classified according to the type of hydrocarbon group into: 1. Alkyl halides( R-X); compounds contain the C-X bond where X is a halogen (F, Cl, Br or I) bonded to one sp3 hybridized carbon atom Note that the halogen atom is more electronegative than carbon therefore the bond is polarized with the electron density concentrated on the halogen as shown in the electrostatic maps of CH3-X molecules below.

Classes of alkyl halides: They are classified according to the type of carbon atom bearing the halogen into: Primary alkyl halide CH3-X and R-CH2-X Secondary alkyl halide (R)2-CH-X Tertiary alkyl halide (R)3-C-X Examples:

has a halogen atom bonded to one sp2 hybrid C atom 3. Allyl halide C=C-C- X 2.Vinylic halide C=C-X has a halogen atom bonded to one sp3 hybrid C atom but in third position of allylic group has a halogen atom bonded to one sp2 hybrid C atom CH2=CHBr Vinyl bromide Bromoethene Ex. CH2=CHCH2Cl Allyl chloride Ex. 4. Benzylic halide: Ar-C-X has a halogen atom bonded to Carbon that one atom away from aromatic ring 5. Aryl halides: Ar-X (X directly attached to phenyl ) has a halogen atom bonded directly to an aromatic ring

Nomenclature OF Alkyl halides IUPAC names derived from the names of parent organic compound (alkane or alkene or alkyne or alcohol or aldehyde and so on) with a prefix indicating halogens and their positions. Common names derived from the corresponding alkyl group followed by the name of halogen atom. CH3-Cl CH3-CH2-Br (CH3)2-CH-F Common Methyl Chloride Ethyl bromide Isopropyl fluoride IUPAC Chloromethane Bromoethane 2-Fluoropropane Class 1° 1° 2° Common Cyclohexyl Iodide t-Butyl bromide Methylcyclopentyl bromide IUPAC Iodocyclohexane 2-Bromo-2- methylpropane 1-bromo-1-methyl cyclopentane Class 2° 3 ° 3 °

Physical Properties Solubility : All organic halides are insoluble in water and soluble in common organic solvents. Boiling point : The boiling points increases with increasing in molecular weights. Therefore, the boiling points increases in the order F < Cl < Br < I Alkyl halides have higher melting points than alkanes, alkenes, alkynes because of: 1. Polarity 2. Molecular weight

Preparation Of Halocompounds 1- Direct Halogenation of Hydrocarbons Halogenation of alkanes b) Halogenation of alkenes Examples:

c) Halogenation of alkynes Examples:

d) Halogenation of alkyl benzene and aromatic ring N.B.

2- Conversion of alcohols

Reactions of Organic Halides 1- Nucleophilic Substitution Reactions

2- Elimination Reactions: Alkyl halides can lose HX molecule to give an alkene If the haloalkane is unsymmetrical (e.g. 2-bromobutane or 2-bromopentane) a mixture of isomeric alkene products is obtained.

3) Formation of Grignard reagent and its reactions a) Formation of Grignard reagent b) Reactions of Grignard reagent Reactions of Grignard reagent with aldehydes and ketones will be discussed in alcohol chapter

4- Reduction of alkyl halides a) Reduction by Zinc metal and acids or by metal hydrides b) By sodium metal (Coupling reaction) (Wurtz reaction) Symmetrical alkane c) Reduction using lithium dialkyl cuprate

Thank You for your kind attention ! Questions?