1. Organic Halogen Compounds
Dr Nahed Elsayed 1

2. 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)

3. 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.

4. 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:

5. 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

6. 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 Fluoropropane
Class ° ° °
Common Cyclohexyl Iodide t-Butyl bromide Methylcyclopentyl bromide
IUPAC Iodocyclohexane Bromo-2- methylpropane bromo-1-methyl cyclopentane
Class ° ° °

7. 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

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

9. c) Halogenation of alkynes
Examples:

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

11. 2- Conversion of alcohols

12. Reactions of Organic Halides
1- Nucleophilic Substitution Reactions

13. 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.

14. 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

15. 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

20. Thank You for your kind attention !
Questions?