Cabocation NMR

The carbocations (2) and (3) only differ in the positions of electrons, so they are resonance forms of the same ion, and can be described as a non-classical carbocation. NMR evidence for the non-classical nature of such cations is given in March (6th ed.), pp. 1582–1583.

Wagner-Meerwein shift

Camphene hydrochloride–isobornyl chloride rearrangment

J. Org. Chem. (1999) 64, 60–64

In the presence of a Lewis acid catalyst, camphene hydrochloride (1) rearranges to isobornyl chloride (2).



The mechanism is believed to involve the following steps:

• the Lewis acid catalyst abstracts chloride from camphene hydrochloride (1), leaving behind a tertiary carbocation (2)
• the tertiary carbocation (2) rearranges to a secondary carbocation (3) by a [1,2]-alkyl shift
• a chloride ion adds to the secondary carbocation (3), forming isoborny chloride (4)

The OH of 3-cyclohexenol can be removed using superacid:

The NMR of the cation can be recorded, at -80°:

The central 141.9 ppm carbon is typical of a double bond.

The 224.4 ppms are highly deshielded, but not as much as a localized carbocation, which would be around 330 ppm: