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Organic photochemistry and pericyclic reactions (CY50003) 3-0-0. Course content.

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Course content
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
Books

  • CRC Handbook of Photochemistry and Photobiology. Eds by. William M. Horspool and Pill-Soon Song. 1994. CRC Press. ISBN: 0-8493-8634-9

  • Synthetic organic photochemistry. Eds by. William M. Horspool, Plenum press. 1984. ISBN: 0-306-41449-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
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
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)



Immersion Well Reactors

Components

# Lamps

# Immersion wells

# Reaction flasks

# Standard flasks

# Gas inlet flasks

# Flow-through flasks

# Larger capacity standard flasks


Non-Rotating AnnularPhotochemical 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: three lamp modules. Each module contains two lamps.


Purity of solvent and gases
Purity of solvent and gases three lamp modules. Each module contains two lamps.

  • 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)


Transmission characteristics of various solvents three lamp modules. Each module contains two lamps.

Measured for a 1cm path length of pure solvent


Photochemical synthesis of oxetans

Photochemical synthesis of oxetans three lamp modules. Each module contains two lamps.

Paternò-Büchi Reaction


Norish Type I Processes of Ketones Basic Concepts three lamp modules. Each module contains two lamps.



JACS, 1977, 99, 3723-33 1,4-biradicals formed by


Mechanism I 1,4-biradicals formed by


Bioluminescence 1,4-biradicals formed by

Fireflies

Artistic rendering of bioluminescent Antarctic krill

Firefly luciferin


Image of bioluminescent 1,4-biradicals formed by red tide event of 2005 at a beach in Carlsbad California showing brilliantly glowing crashing waves

containing billions of Lingulodinium polyedrumdinoflagellates




Photo removable protecting groups

Photo removable protecting groups 1,4-biradicals formed by


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