Presentation on theme: "Organic photochemistry and pericyclic reactions (CY50003) 3-0-0."— Presentation transcript:
Organic photochemistry and pericyclic reactions (CY50003) 3-0-0
Course content Principles of photochemical reactions; Excited states and their properties; experimental set up for photochemical reactions(1); Several useful photochemical reactions and their applications in organic synthesis (isomerization, Patterno-Buchi reaction (1), Norrish type I and II reaction(1), Photoreduction, Rearrangements: di-π- methane, oxa di-π- and aza di-π-methane rearrangements(2), Photocycloaddition (2), Photochemical aromatic substitution reaction (1), Reactions with singlet oxygen (1), Photochemical methods for protection and deprotection(2). Photochemistry of biological systems (photosensitized reactions of DNA/RNA, DNA damage and repair-1).
Books CRC Handbook of Photochemistry and Photobiology. Eds by. William M. Horspool and Pill-Soon Song CRC Press. ISBN: Synthetic organic photochemistry. Eds by. William M. Horspool, Plenum press ISBN: X
LIGHT ABSORPTION AND FATE OF EXCITATION ENERGY: Franck-Condon Principle Ground state (E0) and two excited states (E1, E2) of a molecule (vibrational and rotational levels are not shown).
Criteria of an ideal sensitizer It must be excited by the irradiation to be used, small singlet triplet splitting. High ISC yield. It must be present in sufficient concentration to absorb more strongly than the other reactants under the condition. It must be able to transfer energy to the desired reactant, low chemical reactivity in Triplet state.
Experimental set up for photochemical reactions Synthetic organic chemist (high intensity light source, easy to handle, various Flask size, specially designed systems) Physical chemist or physical-organic Chemist (mechanistic study)
Wavelength of cutoff (nm)Chemical composition Below 250Na 2 WO 4 Below 305SnCl 2 in HCl (0.1 M) Below 3302M Na 3 VO 4 Below 355BiCl 3 in HCl Below 400KH phthalate + KNO 2 (in glycol at pH = 11) Below M K2CrO 4 (NH 4 OH-NH 4 Cl at pH = 10) Above 3601 M NiSO 4 + 1M CuSO 4 (in 5% H 2 SO 4 ) Above 450CoSO 4 + CuSO 4 Short and Long cutoff filter solutions
Immersion Well Reactors Components # Lamps # Immersion wells # Reaction flasks # Standard flasks # Gas inlet flasks # Flow-through flasks # Larger capacity standard flasks
Non-Rotating Annular Photochemical Reactor # Large Quartz immersion well. # 400 watt medium pressure mercury lamp. # Reactor base and carousel assembly (non rotating), including support rod and immersion well adjustable clamp. # set of sample tube support rings for eight 25mm sample tubes # Only the inner or the outer tubes may be irradiated effectively at one time # UV Screen:- consisting of three black coated consisting of three black coated aluminum sections. A light tight lid, a removable front and back section, that are joined by means of a light tight seal
Semi-Micro Reactor The semi-micro is a low cost, easy-to-use device for irradiating a standard 1 cm cuvette (or small tube) with either 254nm or 350nm radiation for any preset time between 1 and 70 minutes. This reactor is ideal for preliminary studies of small volumes of solution.
# The multilamp reactors consist of a base, lid, six or three lamp modules. Each module contains two lamps. # The base is hexagonal and provided with a centrally located fan # A number of modules up to six or three may be operated. # Switches are provided to control the fan and lamp modules. # Supports from the lid hold samples inside the reactors. Magnetic strips are used to eliminate light leaks between the lamp modules. Multilamp Reactors: Six and Three Modules
Complete photochemical reactor comprising: * Multilamp reactor base with cooling fan and control switches * Three twin lamp modules * Six lamps of customers choice * Magnetic light sealing strips One set of attachments for supporting the reaction flask comprising : * Reaction flask support base * Flask support rod holder * Support rod hinged lid
Purity of solvent and gases Dilution (suppression of side reaction e.g., polymerization and dimerization.) Spectral transmission of solvent ( solvents devoid of low-lying excited states are best) Purity of solvent (Oxygen free, impurities free)
Solvent10% Transmission (nm)100% Transmission (nm) Acetone Acetonitrile Benzene Carbon Tetrachloride Cyclohexane Diethyl ether Dimethyl sulfoxide Ethanol Hexane Propan-2-ol Tetrahydrofuran Transmission characteristics of various solvents Measured for a 1cm path length of pure solvent
Photochemical synthesis of oxetans Paternò-Büchi Reaction
Norish Type I Processes of Ketones Basic Concepts
Norish type II photoelimination of ketones: Cleavage of 1,4-biradicals formed by γ - hydrogen abstraction
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