REACTION INTERMEDIATES: CARBENE, NITRENE &

ARENE/BENZYNE

By:

Neha JainMs. Neha Jain

(M.Sc., M.Phil, Research Scholar)Laboratory of Endocrinology, Department of Biosciences,

Barkatullah University,Bhopal-462026, M.P., India

2

Reaction Intermediates1. If a reaction occurs in more than one step, it must involve

species that are neither the reactant nor the final product.2. These are called reaction intermediates or simply

“intermediates”3. Each step has its own free energy of activation.4. Reactive intermediates are usually short lived and are very

seldom isolated.5. The complete diagram for the reaction shows the free energy

changes associated with an intermediate.

For example, consider this hypothetical stepwise reaction:A + B → C + DThe reaction includes these elementary steps:A + B → X*X* → C + DThe chemical species X* is an intermediate.

Types of Reaction Intermediates

CARBOCATION

CARBANION

FREE RADICLE

CARBENE

NITRENE

ARENE/BENZYNE

5

CARBOCATION, CARBANION & FREE RADICLE

6

CARBENE

DESCRIPTION•This is the species with central carbon atom with two bonds and two electrons. •These are uncharged species and 6 valence electrons.•These electrons are may be paired or unpaired. •These are very short lived species. •The smallest and simplest species of this class is methylene, this is non isolable species.When the electrons are paired the Carbene has singlet state and in case of unpaired electrons the Carbene has triplet state. These are extremely reactive species and can beAs these species are short lived and very reactive hence it is difficult to detect.

FORMATION

REACTION

NITRENE

DESCRIPTION1. Nitrene is electro-neutral monovalent electron

species.2. This has similar properties as that of carbene.

Hence Nitrene is called as nitrogen analogue of carbene.

3. There are six electrons present on nitrogen in Nitrene.

4. Carbenes are less stable than Nitrene.5. Generation of Nitrene is possible in both triplet

and singlet state but mostly the ground state for Nitrene is triplet.

REACTIONS

ARENE/BENZYNE

DESCRIPTION1. It is non isolable very reactive species with the hexagonal

planar rind structure with 6 pi delocalizing and 2 additional pi electrons.

2. The addition two pi electrons do not affect the aromatic character of ring as it does not interfere with the Huckel number.

3. This is a six membered ring containing C-C triple bond this triple bond gives high reactivity to the species.

SYNTHESIS

REACTIONS

REFERENCESA Kulkarni and Kalyani. D. Asgaonkar Study of

Various Reaction Intermediates Juilee., P 325 -351, Vol. 3 (1) Jan – Mar 2012 www.ijrpbsonline.com

Sachin Kumar Ghosh, General organic chemistry, A modern approach, fundamentals of organic reaction mechanism, new Alipore college New central book agency, May 1994, 384-403.

www.wikipedia.com

Thanks !!!