Ronald George Wreyford Norrish developed Norrish reaction

Ronald George Wreyford Norrish – inventor of norrish reactions

Category : Personalities
Published by : Data Research Analyst, Worldofchemicals.com

Biography & Contributions

Ronald George Wreyford Norrish was a British chemist and Nobel laureateborn on November 9, 1897 - died on June 07, 1978. He was the developer of Norrish reaction1978. 

In 1967 Norrish received Nobel Prize. He also researched on photochemistry concepts. Norrish investigated the correlation between photodecomposition and spectral character, phosphorescence, and other physical phenomena.

Norrish reactions

The Norrish reaction in organic chemistry describes the photochemical reactions taking place with ketones and aldehydes. It is subdivided in Norrish type I reactions and Norrish type II reactions.

Norrish type I reaction

Norrish type I reaction is the photochemical cleavage or homolysis of aldehydes and ketones into two free radical intermediates.

Mechanism

Step 1]

Absorbtion of UV light (230-330 nm) leads the molecule to singlet excited state(s) which is converted to triplet excited state (T) by intersystem crossing.

Step 2]

Fragmentation of C-C bond adjacent to -C=O group to acyl radical or allyl radical.

Step 3]

In case of unsymmetrical ketone, the cleavage depends on stability of different radicals.

Step 4]

The two different radicals further react to give different products i.e. hydrocarbon, ketone and alkene.

Pictorial representation

Norrish type II reaction

Norrish type II reaction is the photochemical intermolecular abstraction of a γ-hydrogen by the excited carbonyl compound to produce a 1,4-biradical as a primary photoproduct.

1. Simple cleavage into radical

A-B-C → A-B + C

2. Decomposition into molecule

A-B-C → X + Y

3. Intramolecular rearrangement

A-B-C → A-C-B

4. Photosensitization

A-B-C → A-B-C*

5. Hydrogen atom abstraction

6. Photodimerisation

A-B-X → (ABX) 2

Pictorial representation

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