CHE-20055 Radicals - Free Radical Chemistry

Flashcards for reviewing free radical chemistry lecture notes.

What is the simple definition of a radical?

Any species with an unpaired electron.

What skills/tools will be utilized in this course?

Lewis structures, curly arrows, and molecular orbital diagrams.

What does a 'normal' curly arrow represent?

The motion of two electrons.

What does a half-headed arrow signify?

The movement of ONE electron.

What is a useful measure of thermodynamic radical stability?

The bond dissociation energy for the corresponding C-H bond.

What is the hybridization of carbon in aryl radicals?

sp2 hybridization.

How is radical stability measured?

By using the bond dissociation energy for the corresponding C-H bond.

What happens when sigma bonds are broken?

The phenomenon is usually described as hyperconjugation.

What is the relationship between the energy of original orbitals and perturbation in the mixed orbitals?

Being equal, the closer the original orbitals are in energy, the greater the perturbation in the mixed orbitals

What are some radical 'destroying' reactions ('Termination')?

radical-radical combination (recombination) and radical-radical disproportionation.

Give two examples of 'propagation' reactions:

Atom abstraction and Addition to multiple bonds.

Name two ways radicals can be generated:

Thermal cleavage & Photo Cleavage

Name two ways radicals can be generated:

1 electron reduction of cations or cation-like species & 1 electron oxidation of anions or anion-like species

What is a propagation reaction?

A reaction where atoms are abstracted or added to multiple bonds.

What happens if we want radical-radical combination?

We should be generating our radicals in high concentration.

What action should you take if we want to avoid radical-radical combination?

We need to control the formation of our radicals so that the concentration is low.

What are some of the limitations of using Lithium Aluminium Hydride reduction?

Practically all carbonyl groups and other groups like nitriles will also be reduced.

What are some of the limitations of using Grignard reagents?

practially all carbonyl groups etc would be incompatible

Why is the C-H bond quite strong?

because there is good orbital overlap (both in terms of spacial overlap and 'energy matching')

Why is Tin a good hydrogen atom donor?

Because we are looking for a weak bond to hydrogen (and therefore a good hydrogen atom donor) we probably want something lower down the periodic table.

What kind of solvent is used for the Wohl-Ziegler reaction?

CCl4 (usually)

What is the purpose of using NBS in the Wohl-Ziegler reaction?

NBS acts like a source of Br2.