Organic Chemistry: Reaction Mechanisms II

substitution reaction

only single bond is present between two atoms

free radical substitution reaction

it takes place in the presence of light or peroxide.

nucleophilic substitution reaction

if a single bond is present between two electronegative atoms.

electrophilic substitution reaction

it takes place in aromatic compounds like benzene.

addition reaction

it takes place in a pie-bond containing compounds.

free radical addition reaction

pie-bond present between same electro-negative elements in presence of peroxide (alkene, alkyne)

nucleophilic addition reaction

pie-bond present between different electronegative elements

electrophilic addition reaction

pie- bond is present between the same electro negative (alkene and alkyne)

elimination reaction

it gives alkene, alkyne and cyclic compounds.

hydrohalogenation of alkene

it follows markonikov's rule (the chlorine gets attached to the carbon having less number of hydrogen)

hydration of alkene

• water acts as a nucleophile and gives no reaction
• it requires dil h2so4, h30+, h2o/h+ to get the final product

halogenation of alkene

• when alkene reacts with halogen 1,2 dihaloalkane is formed.

addition of hypohalous acid

• HOCl > HOBr > HOI (reactivity order)
• when alkane reacts with hypohalous acid, halohydrine is formed.
• follows markonikov's rule

addition of tiden's reagent

• NO+Cl-
• propylenenitrosylchloride is formed

oxymercuration-demercuration reaction

• markonikov's rule
• forms secondary alcohol
• reagent: Hg(OCOCH3)2.H2O, NaBH4, NaOH
• alkene reacts with mercuric acetate followed by treatment with sodium borohydride in basic medium.

hydroboration reaction

• anti-markonikov's rule
• primary alcohol
• reagent: B2H6, H2O2, OH-
• when alkene reacts with diborane then tri-alkyl borane is formed.
• no rearrangement possible
• syn/cis addition takes place

trialkyl borane

• H2O/OH- ---> PRIMARY ALCOHOL
• CH3COOH ---> ALKANE
• NH2CL ---> AMINE
• CL2 -->ALKYL HALIDE
• AGNO2 ---> DIMERISATION

markonikov's rule

• negative part of the reagent is attached to those carbon of the unsymmetrical alkene which has the minimum number of hydrogen.
• -M, -H, -I, symmetrical alkene it fails

--anti-markonikov's rule

• negative part of the reagent is attached to the carbon of the unsymmetrical alkene which has more number of hydrogen in the presence of peroxide.
• kharasch rule/ peroxide effect
• failed in case of symmetrical alkene
• also failed in case of HCL, HBr, HI

electrophilic addition reaction

directly proportional to the stability of carbocation
directly proportional to (-M,-H,-I) & electron donating tendency

reactivity

alkene > alkyne
sigma bond resonance is more stable than pie bond resonance

free-radical addition

free-radical attacks on substrate molecule to form product.

Kucherov reaction (addition of h2o to alkyne)

• reagent: dil h2so4/hg2+
• to form enol
• then it further tautomerism to acetone

addition of alcohol

• in the presence of BF3 and HgO, alkyne reacts with alcohol to form acetal and ketal.

addition of AsCl3

• alkyne reacts with AsCl3 to form lewisite gas which is a poisonous gas.

nucleophilic addition reaction

• nucleophile attacks on the substrate
• directly proportional to magnitude of +charge if sp2 hybridized carbon
• inversely proportional to steric hindrance
• directly proportional to -M,-H,-I (electron withdrawing group)

addition of HCN

• carbonyl compound reacts with HCN to form cyanohydrin.
• cyanohydrin --> (partial hydrolysis) lactamide
• cyanohydrin --> (complete hydrolysis) lactic acid
• cyanohydrin --> (reduction LiAlH4) hydroxyamine/aminoalcohol