[maakii]

Hi everyone,

I know that free radicals are very much stabilised by methyl groups by hyperconjugation as well as other side groups which can have resonance like phenyl rings and carbonyl groups.

However, is a free radical actually negatively or positively charged?

Since I think that the answer is that it is neutral, would this mean that electron withdrawing groups like -NR₄+ and electron donating groups which are incapable of resonance would not stabilise free radicals?

Thanks!

[Custos]

A radical can be neutral, positive or negatively charged.

If an anion is oxidised (loss of an electron) you get a neutral radical. So for example the phenoxide ion can be oxidised by Fe³⁺ to give the neutral phenyl oxygen radical while Fe³⁺ is reduced to Fe²⁺. Also if a neutral molecule is split (called homolytic bond fission), for example Br₂ going to two Br^. radicals, you get neutral radicals. Neutral radicals are the most common in solution.

You can get radical anions and radical cations by adding or removing (respectively) a single electron from a neutral species. This behaviour is most commonly seen in the gas phase, for example in mass spectroscopy.

[organoman]

Please somebody put some more thought or some link for reference as so far even I was under impression that free radicals are only neutral.
regards,
ORG

[Mitch]

In the context of organic chemistry. A 'stable' free radical in sloution is likely also neutral.

[AhmedEzatAlzawalaty]

i dont think there is a stable radical since what makes it reactve is its unstability and i think all radicals very raective

[P]

i dont think there is a stable radical since what makes it reactve is its unstability and i think all radicals very raective

Type "TEMPO Radical" into Google  -  it is a stable free radical  -  there are others as well.   It will still react -  but exists fairly stably on its own.

[mir]

i dont think there is a stable radical since what makes it reactve is its unstability and i think all radicals very raective

What drives radicals to reaction is all about kinetics, not thermodynamics. So if you can slow down the kientics by hindering the radical center, you could end up with stable radicals like that already mentioned TEMPO. You might also combine the hindering effect with resonance stabilization.

[Yggdrasil]

I think monodehydroascorbate, a free radical form of vitamin C, is a fairly stable radical.