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In radical elimination, an unstable radical compound breaks down into a spin-paired molecule and a new radical compound. Shown below is an example of a radical elimination reaction, where a benzoyloxy radical breaks down into a phenyl radical and a carbon dioxide molecule. [7] A radical elimination reaction of a benzoyloxy radical
The ethoxy and cyano groups are able to delocalize the radical ion in the transition state, thus stabilizing the radical center. The rate enhancement is due to the captodative effect. When R = H, the reaction has the largest energy of activation because the radical center is not stabilized by the captodative effect.
In chemistry, chemical stability is the thermodynamic stability of a chemical system, in particular a chemical compound or a polymer. [1] Colloquially, it may instead refer to kinetic persistence , the shelf-life of a metastable substance or system; that is, the timescale over which it begins to degrade.
In the mid-1960s, the dimer form of the radical was observed, and instead of forming the expected Ph 3 CCPh 3 product, the radical instead undergoes head to tail addition. By contrast, adding two t Bu groups to the meta positions on the phenyl rings causes the radical to readily dimerize to (3,5-t Bu 2 H 3 C 6) 3 C–C(C 6 H 3-3,5-t Bu 2) 3. [1]
The inductive effect can be used to determine the stability of a molecule depending on the charge present on the atom and the groups bonded to the atom. For example, if an atom has a positive charge and is attached to a - I group its charge becomes 'amplified' and the molecule becomes more unstable.
Although the exo radical is less thermodynamically stable than the endo radical, the more rapid exo cyclization is rationalized by better orbital overlap in the chair-like exo transition state (see below). (1) Substituents that affect the stability of these transition states can have a profound effect on the site selectivity of the reaction.
In chemistry, radical initiators are substances that can produce radical species under mild conditions and promote radical reactions. [1] These substances generally possess weak bonds—bonds that have small bond dissociation energies. Radical initiators are utilized in industrial processes such as polymer synthesis.
Hyperconjugation can be used to rationalize a variety of chemical phenomena, including the anomeric effect, the gauche effect, the rotational barrier of ethane, the beta-silicon effect, the vibrational frequency of exocyclic carbonyl groups, and the relative stability of substituted carbocations and substituted carbon centred radicals, and the thermodynamic Zaitsev's rule for alkene stability.