Halocompounds

• Completely halo substituted HCs have prefix Perhalo
• Alkyl halides - halogen is linked to sp3 C of an alkane
• Alkyl halides can be 1°, 2°, or 3°.
• Allylic halides - Halogen is linked to sp3 C which is bonded to olefinic group.
• Allylic halides can be 1°,2° or 3°
• Benzoyl halides - halogen is linked to sp3 C directly attached to Benzene ring
• cycloalkyl halide = alkenyl halide
• alkenyl halide - halogen is linked to sp3 C in a ring
• Vinylic halides - Halogen is linked to sp2 C of an alkene
• Aryl halides - halogen is directly linked to benzene ring
• Acid halides - halogen is bonded to alkyl ketonic group
• Chloramphenicol (natural) to control typhoid fever
• Thyroxine (natural) to bring down goitre disease
• Chloroquine (synthetic) to control malarial fever
• Halothane (synthetic) as anaesthetic in surgery
• Iodoform (synthetic) as anaesthetic
• Bithional (synthetic) an antiseptic in soap
• Westron/ Westrosol (synthetic) as solvents
• BHC/DDT (synthetic) as pesticides/insecticides
• Teflon (synthetic) in nonstick cookware
• Vinyl chloride (as pvc) (synthetic) water pipes
• Halo compounds exhibit 1. Structural isomerism - chain and positional

  2. Stereoisomerism - conformational, geometrical and optical
• HCs with a chiral carbon can exhibit optical isomerism
• Isomers which exhibit optical isomerism exist in 2 forms differing in optical activity
• Optical isomers are mirror images of one another that cannot be superimposed on one another
• Alkyl halides - CnH(2n+1)X
• A chiral carbon is a carbon with 4 different groups attached to it.
• Chiral C represents stereogenie centre of that molecule
• A carbon with 2 similar atoms or groups is called nonchiral carbon
• Direct halogenation of alkanes occurs in the presence of sunlight or at high temp (at 420° C) alkane undergoes FR substitution with Cl2 or Br2 to form respective haloalkanes
• In direct halogenation when Cl is taken in excess a mix of diff chloroalkanes which are hard to separate cause of their close BPs
• Alkane in excess than halogen forms monohaloalkane
• Reactivity order : F2> Cl2> Br2> I2
• Ease of replacement of H : 3°>2°>1°
• Direct flourination = less feasible cause fluorine has high reactivity and reaction is violent
• Direct iodonation is a reversible process hence it is carried out by using oxidising agents like conc. HNO3 or HIO3 (they oxidise HI to I2 or HIO3 and prevent backward reaction)
• Alkyl fluorides and alkyl iodides are better prepped via halogen exchange method
• Halogen exchange methods include Feinkelsteins reaction and Swart’s reaction
• Fienkelstei’s reaction is conversion of alkyl chloride/bromide to alkyl iodide using NaI in dry acetone
• The role of dry acetone is to precipitate NaCl or NaBr so as to prevent backward reaction