Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

226 BOKNBOL AND CAMPHBNB
Here also formally OH exchanges its place with an alkyl radicle,
CH3, although actually—since concentrated sulphuric acid is used—
the elimination of water between the two OH-groups provokes the
wandering of a methyl .group.
A rearrangement which takes place in similar compounds, and
has been much studied recently, may be briefly mentioned here.
This rearrangement has been named—not quite correctly—the retropinacoline
rearrangement.
It consists in the conversion of pinacolyl alcohol into tetramethylethylene
with elimination of water:
-C CH, ~
CH
Ha CH, CH3
°,
1 y \
CH, H 0H Closely related to this change is the conversion of borneol and its
derivatives into compounds of the camphene type :
CH CH CH
CH,
' CMe21 CHOH
CH,
Borneol Camphene
The only difference between the two reactions evidently consists
in the shift of the double bond in respect of the methyl group, from
a, b, to b, c. For between a and b, through stereochemical reasons, no
double bond can exist, since, in accordance with Bredt's rule, none of
the C-atoms which are common to both rings of a bicyclic system of the
camphene type can take part in an unsaturated linkage.
Further inspection shows the second of the above camphene formulae
to be merely another and more convenient way of writing this hydrocarbon.
Information about this important work, which can be considered
only briefly here, is to be derived from the publications of H. Meerwein.
A clear and comprehensive review of our knowledge of molecular rearrangements
is to be found in : Henrich, Theorien der organischen
Ghemie, 5th Ed., 1924, Chap. XVII. See also W. Hiickel, Theoretische
Grundlagen der organischen Ghemie, Leipzig, 1931, Vol. I. p. 210.
Only one more rearrangement of benzil, leading to an elegant preparative
method, need be mentioned here, namely its conversion into