Initiator half-life (t1/2)
the time required for the reacting species to reduce to half its initial concentration at a given temperature in a particular solvent
How do EDG and EWG like to position themselves on a ring with double bonds?
- EDG always sit on the double bond
- EWG avoid the double bond
Stability of radicals
like alkyls
3º > 2º > 1º > methane
How can radicals be stabilised?
- Delocalisation into π systems (allyl, benzyl)
- Electron-withdrawing groups (EWG)
- Electron-donating groups (EDG)
What is the captodative effect?
Stabilisation of a radical by both an EWG and an EDG simultaneously.
Example of captodative stabilisation?
Isobutyronitrile radical from AIBN (CN = EWG, alkyl = EDG).
What technique is used to detect radicals?
Electron spin resonance (ESR) / Electron paramagnetic resonance (EPR).
What does EPR measure?
Transitions between spin states of unpaired electrons in a magnetic field.
Why do radicals give splitting in EPR?
Interaction with nearby nuclei (e.g. hydrogens).
What is the pinacol coupling reaction?
Coupling of two carbonyl compounds to form a 1,2-diol (pinacol)
What type of reaction is pinacol coupling?
Radical–radical coupling.
What reagents are used?
Low-valent metals (e.g. Mg, Na, Li).
What is formed before workup?
Metal-coordinated intermediate (template system).
How is active Ti species generated?
Reduction of TiCl₃ using Zn.
What is the “instant method”?
Ti species generated in situ in presence of carbonyl.
