alkyl halides

Question 1

 Nucleophile

Answer 1

 Electron rich species
 Having unshared pair of electrons available for bonding
 Mostly basic in character
 Negatively charged or neutral
 nucleus loving

Question 2

 Electrophile:

Answer 2

 Electron deficient specie
 Carbon attached to halogen bears partial positive charge and is Electrophilic in character
 Electrophile may be neutral or positively charged.
 e- loving

Question 3

 Leaving group:

Answer 3

 Leaving group is the group which departs with an unshared pair of electrons.
 It departs when comparatively stronger nucleophile approaches.
 Good leaving groups include: Cl-, Br-, I- and HSO4-
 Poor leaving groups include: OH-, OR- and NH2-

Question 4

 Substrate:

Answer 4

 The alkyl halide molecule on which a nucleophile attacks is called a substrate molecule.

Question 5

Nucleophilic Substitution Bimolecular (SN2)

Answer 5

 Single step
 The extent of bond formation is equal to the extent of bond breakage.
 Transition state exists
 Coming nucleophile always attack from side opposite to leaving group.
 The substrate carbon atom changes its state of hybridization from tetrahedral sp3to planar sp2 in transition state.
 The attack of the nuclephile, the change in the state of hybridization and the departure of the leaving group, everything occurs at the same time
Inversion of configuration (Stereochemistry)
 Rate = k [Alkyl halide]1 [Nucleophile]1
 2nd order reaction (Chemical kinetics

Question 6

Nucleophilic Substitution Unimolecular (SN1)

Answer 6

 Two step process; first step involves reversible ionization and second step involves the attack of nucleophile
 Intermediate state exists
 Coming nucleophile attacked from both sides
 Ionization is carried out in aqueous acetone or aqueous ethanol.
 First step is the rate determining step.
 Racemic mixture (50% retention of configuration and 50% inversion of configuration) is formed (stereochemistry)
Rate = k [Alkyl halide]
 1st order reaction (chemical kinetics)