Chemistry

17 Alkyl Halides and Amines197Key Points Monohalo derivates of alkanes are called alkyl halides. The general formula of alkyl halides in CnH2n+1X. The best method for the preparation of alkyl halides is by the reactions of alcohols withinorganic halides like SOCl2, PX3 and PX5. Alkyl halides are very reactive class of organic compounds. They undergo nucleophilicsubstitution reactions and elimination reaction in the presence of nucleophile or a base. Nucleophilic substitution reactions can take place in two distinct ways. A one stepmechanism is called SN2 while a two step mechanism is called SN1. SN1 reaction showfirst order kinetics whereas SN2 reaction show 2 nd order kinetic. Nucleophilic substitution reactions take place simultaneously with elimination reactionand often compete with them. Elimination of two atoms or groups from adjacent carbon atoms in the presence of anucleophile or a base is called elimination reaction. Like nucleophile substitution,β-elimination reactions also take place in two distinct ways E2 and D1. A nucleophile is an the electron rich species that will react with an electron poor species A substitution implies that one group replaces another. Grignard reagent can be prepared by adding alkyl halide in a stirred suspension ofmagnesium metal in diethyl ether. Grignard reagent ahs a reactive nucleophilic carbon atom which can react withelectrophilic centered to give the products in high yields. Primary, secondary and tertiaryalcohols can be best prepared by reacting Grignard reagent with formaldehyde, any otheraldehydes and ketones, respectively. The polar nature of the N-H bond (due to the electronegativity difference of the two atoms)results in the formation of hydrogen bonds with other amine molecules. Primary amines, R-NH2 or ArNH2, undergo nucleophilic addition with aldehydes orketones to give carbinolamines which then dehydrate to give substituted imines. Primary alkyl or aryl amines yield diazonium salts.Exercise1. Choices given with each question.i. In primary alkyl halides, the halogen atom is attached to a carbon which is furtherattached to how many carbon atoms;a. Two b. Three c. One d. Fourii. SN2 reactions can be best carried out with:a. Primary alkyl halides b. Secondary Alkyl halidesc. Tertiary alkyl halides d. All the three