CBSE Class 12 Chemistry Haloalkanes Haloarenes Summary

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HALOALKANES

INTORDUCTION:

The replacement of hydrogen atom(s) in a hydrocarbon, aliphatic or aromatic, by halogen atom(s) results in the formation of –alkyl halide (haloalkane) and aryl halide (haloarene), respectively. Haloalkanes contain halogen atom(s) attached to the sp3 hybridised carbon atom of an alkyl group whereas haloarenes contain halogen atom(s) attached to sp2 hybridised carbon atom(s) of an aryl group.

Many Halogen containing organic compounds are clinically useful & find wide applications in industry as well as in day-to-day life.

Examples: 1. Chlorine containing antibiotic, chloramphenicol, produced by soil microorganisms is effective for the treatment of typhoid fever.

2. Our body produces iodine containing hormone, thyroxine, the deficiency of which causes a disease called goiter.

3. Chloroquine is used for the treatment of malaria;

4. Halothane is used as an anaesthetic during surgery.

5. Certain fully fluorinated compounds are being considered as potential blood substitutes in surgery.

6. Haloalkanes are used as solvents for relatively non-polar compounds and as starting materials for the synthesis of wide range of organic compounds.

CLASSIFICATION

1.On the Basis of Number of Halogen Atoms-mono, di, or polyhalogen (tri-,tetra-, etc.) compounds depending on whether they contain 1, 2 or more halogen atoms in their structures.

NOMENCLATURE

1. The common name of alkyl halide =name of the alkyl group followed by the halide (i.e. Alkyl halide)

2. IUPAC name of Alkyl halide = halo substituted hydrocarbons (i.e. Haloalkane)

3. Haloarenes are the common as well as IUPAC names of aryl halides. For dihalogen derivatives, the prefixes o-, m-, p- are used in common system but in IUPAC system, the numerals 1,2; 1,3 and 1,4 are used.

4. The dihalogen derivatives having same type of halogen atoms on the same carbon are known as geminal dihalides and assigned common name alkylidene halides or alkylidene dihalides. The dihalogen derivatives having same type of halogen atoms on adjusant carbon atoms are known as vicinal dihalides and assigned common name alkylene halides or alkylene dihalides.Nature of C-X Bond

 Remember:

1. Polarity affects the physical properties like b.pt., physical state etc. More polar compounds have higher boiling points. That is why B.Pt. of Haloalkanes > B.Pt. of hydrocarbons of comparable molecular mass.

2. Since the size of halogen atom increases as we go down the group in the periodic table, consequently for the same alkyl group boiling points of alkyl halides decrease in the order: RI> RBr> RCl> RF

3. The C atom bears a +δ charge whereas the halogen atom bears a -δ charge. Therefore haloalkanes undergoes nucleophilic substitution reaction, elimination reaction, reaction with metals, reduction.

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