Thermal and Photochemical Reactions

Paper Code: 
CHY 321
Contact Hours: 

To learn about the importance of light in organic reactions.

Unit I: 
Basics of Photochemistry

Electromagnetic radiation, photochemical excitation – interaction of electromagnetic radiation with organic molecules, types of excitations (π → π*, n → π* etc.) fate of excited molecules - Jablonskii diagram, intersystem crossing, energy transfer, photosensitization, quenching, quantum yield, Frank-condon principle Stern-Volmer equation.

Unit II: 
Photochemical Reactions of Carbonyl Compounds

Photochemical reactions of ketones – alpha cleavage or Norrish type I cleavage, gamma hydrogen transfer or Norrish type II cleavage; photo reductions; Paterno-Buchi reactions; photochemistry of α,β-unsaturated ketones, β,γ-unsaturated ketones, cyclohexadienones (cross conjugated and conjugated).

Unit III: 
Photochemistry of Alkenes and Aromatic Compounds

Photochemistry of alkenes: intramolecular reactions of the olefinic bond cis-trans  isomerisation (stilbene), cyclization reactions, rearrangement of 1, 4 and 1, 5-dienes, di-π methane rearrangement.

Photochemistry of aromatic compounds: photochemical rearrangement, photostationary state, 1, 3, 5 – trimethyl benzene to 1, 2, 4-trimethyl benzene.

Miscellaneous Photochemical Reactions: Barton reaction, Photo Fries rearrangement of ethers and anilides, singlet oxygen reactions (Photo oxygenation)

Unit IV: 
Pericyclic Reactions -I

General characteristics, classification, molecular orbital symmetry.
Electrocyclic reactions: theories of explanation (FMO, Woodword-Hoffmann and PMO approach), frontier orbitals of ethylene, 1, 3-butadiene, 1, 3, 5-hexatriene and allyl systems, valence tautomerism.

Unit V: 
Pericyclic Reactions –II

Cycloaddtion Reactions: 2+2, 4+2 cycloaddition, 1, 3-dipolar cycloaddition and cheletropic reactions; stereoselectivity (endo, exo), stereospecific and regioselective hydrogen reactions, Lewis-acid catalysis in Diels’ Alder reaction.

Sigmatropic rearrangements: suprafacial and antarafacial shifts of H, sigmatropic shifts involving carbon moieties, 3, 3- and 5, 5-sigmatropic rearrangements; Claisen, Cope and Aza-Cope rearrangements; isomerization of divinyl cyclopropane; fluxional tautomerism (bullvalene); ene reaction.


Essential Readings: 
  1.  Photochemistry; Horsepool;
  2.  Fundamentals of Photochemistry; First Edition; K.K. Rohatagi – Mukherjee; New Age International Publishers Pvt. Ltd., New Delhi, 2005.
  3.   Molecular Reactions and Photochemistry; First Edition; Charles H. Depuy and Orville L. Chapman; Prentice-Hall of India Pvt. Ltd, New Delhi, 1988.
  4.  Reaction Mechanism in Organic Chemistry; Third Edition; S.M. Mukherjee and S.P. Singh; Macmillan, India Ltd., New Delhi, 1999.
  5.  Advanced Organic Chemistry Part A & B; Fourth Edition; Francis A. Carey and Richard J. Sundberg; Kluwer Academic/Plenum Publishers, New York, 2000.