# Is it possible for a group to substitute itself?

When I first learned about substitution reactions, I started wondering something that I never ended up figuring out:

Suppose you have a strong nucleophile which is also a good leaving group, such as I$^{-}$. Can such a group substitute itself using the SN1 mechanism? If so, would that mean if such a group were bonded to a chiral carbon, an enantiomerically pure solution could spontaneously racemize?

• Very short answer: Yes. Possibly also via SN2. – Martin - マーチン Jul 6 '15 at 1:28
• Has spontaneous racemization been observed? – Rogue Autodidact Jul 6 '15 at 1:36
• see this and this – ron Jul 6 '15 at 1:41
• The reaction you refer to has been done and racemisation observed, however I don't have the reference – Beerhunter Apr 2 '16 at 13:07

• Iodine is quite a good nucleophile for saturated carbon atoms because of its softness. a good nucleophile is a poor leaving group - this statement only really applies to reactions with hard electrophiles like carbonyl groups. – bon May 9 '16 at 9:22