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Recent Investigations on Diterpenes.

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lar weight of about two million. On dissociation, it splits up
into symmetrical particles; the smallest, is still enzymatically
active and has a molecular weight of about 250000. Some
compounds increase dissociation and inhibit enzymatic activity, others increase association and promote activity. These
compounds probably react with thc functional groups of the
enzyme protein or alter its chain conformation. Thus,
both the equilibrium between the individual protein moieties
and the enzyme catalysis can be influenced without the assumption of a direct rclationship between the particle size
and enzyme activity, as was originally thought.
Zinc exercises an important role in reactions catalysed by
ycast and liver ADH. Any action of zinc on other dehydrogenases dependent upon pyridine nucleotide is apparently
based on another mechanism. In the latter, zinc seems to
participate neither in the binding of the coenzyme nor in
hydrogen transport. It is still an open question whether there
are other pyridine-nucleotide-dependentzinc metal dehydrogcnases apart from yeast and horse liver ADH.
[VB 718/97 IE]
German version: Angew. Chem. 75,795 (1963)
Alkylcarbonium and Alkyloxocarbonium Salts
G. A. Oluh, Sarnia, Ontario (Canada)
The structures and chemical rcactivity of several primary,
secondary, and tertiary alkyloxocarbonium (acylium) salts
were investigated by infrared and nuclear magnetic resonance
spectroscopy (IH, 2H, 13C, and 19F) in complexes of the
following type:
lH~CCOIQISbF~lO,D3CCOl@~"SbF& and [H&YCO]@ [SbF&.
--.
The results are compatible with a structure containing a
triple bond, in which however the positive charge is not
localized completely on the oxygen atom, i.e. an oxocarbonium structure IH3C C 01" [SbF6le is actually
present.
The chemical shift of the hydrogen atoms in the above salt
amounts to about 2 ppm, that of the [13C] carbonyl carbon
atom to 45 ppm, compared with acetyl fluoride. In solution
(liquid H F and SOz), the salt is in equilibrium with the
covalent donor-acceptor complex
Polymorphism of Bismuth Oxides
G. Grrr/oiv, GBttingen (Germany)
p-Bi01.50, which is metastable at roo111 temperature, can be
prepared by extremely rapid quenching o f thin films of molten bismuth(ll1) oxide; howcver. on treating R i or Biz03
with C in a graphite boat with oxygen at 800°C or more, a
product with the composition $-HiO;l.5,) results. Using
chemical and X-ray analysis and tiy investigation of the thermal decomposition under isobaric conditions, the phase range
oi the @-modificationof bismuth(lI1) oxide from BiO1.50 to
BiOl.75 was determined. Structural investigations showed
that the P-modification crystallizes i n the space group
Pab2--Dqd and is a two-dimensional supcrstructure of the
high-temperature modification (fi-Bi203); the crystal structure of the latter was determined at 750°C. The lattice dimensions with the reliability factors were: for p-Bi01.50:
a = 10.95 :k 0.02 A, C 5.63 .!: 0.01 A; Rhkl 0,046,and for
$-Bi01.75: a - 10.96 I 0.02A,C. 5.64 !. 0.01 A; Rhk1 r= 0.052.
7:
Consideration of the crystal structure of [I-BiOl.lo shows
that the P-modification can absorb oxy!:en continuously into
the lattice without alteration of thc symmetry until the composition Bi01.75 is attained. This value corresponds to the
upper phase boundary of the p-inodification.
The transformations of thc norn.ial ( x - , (3-, 8-Ri2O3) and oxygen-enriched bismuth(lI1) oxides WOI'C investigated by differential thermal analysis, X-ray phorographs, etc., and the
transformation sequences drawii up. The heats of transfor2.0 :k 0.5 kcal/mole for
mation were of the order Lc
&Biz03 +- P-BizO,, Lt = 6.4 I : 0.8 kcal/mole for P-Biz03 -+
a-Bi203, and Lt = 8.4 I- 0.3 kcal/mole for a-BizO3 S &Biz03
at the appropriate transition temperature.
Starting from P-Bi01.75, the y-modification of bismuth(lI1)
oxide can be prepared free from other oxides. It has the composition BiO1.667 and crystallizcs in the cubic system with a
body-centred lattice and with a .-: 10.250 .!: 0.008 A. The
metastable modifications of P-Bi203. y-Bi203 and 8-Bi203
can be stabilized by addition of oxidcs of other metals.
[Inorganic Chemistry Colloquium a t tile I echnische Hochschule Aachen (Germany) June 25th, 19631
722/99 IEl
-:
German version: Angew. Chem. 75,799 (1963)
F
16+ sH,C--CO + SbFS
Recent Investigations on Diterpenes
The decarbonylation reaction of a t-butyloxocarbonium salt
(pivalylium salt) was followed spectroscopically.
[(CH,),CCO]@ ISbI'61"
7
'
l(CH3)3C]@ [SbFslB
+ CO
The stability of trimethylcarbonium hexafluoroantimonate
(in solution in SO2 or SbF5 at low temperatures) makes it
possible to investigate this compound thoroughly. Alkyl
fluorides, e.g. propyl, butyl, and amyl fluorides readily ionize
in SbF5 to form remarkably stable, solvated SbFs-salts.
Several stable alkylcarbonium salts R [SbF6]O, perdeuterated complexes, and also those with '3C-tabelling on the
positive carbon atom were prepared in solution in SbFs plus
SO2 and investigated primarily by spectroscopy (infrared,
ultraviolet, N M R). The carbonium ions (H3C))2CHCi>,
@
0
7:
C. Ourisson, Strasbourg (France) [I]
A number of new diterpcnes have been isolated from Trachylobium verrucosum (Gaertn.) Oliv. (Cucwdpiniuc), i. c. the plant
from which Madagascar copal can be obtained. Chemical and
spectroscopic investigations showed that a new pentacyclic
skeleton is present in some of these diterpenes. Tetracyclic
compounds containing the k;i urute skeleton, and bicyclic
compounds also occur.
(il
(H3C)?C, and (H3C)2C -CHzCH3 were thereby obtained
and characterised for the first time i n the form of stable
(0
salts. The chemical shift of CH - amounts to nearly 10 ppm
8
8
(or 600 cps at 60 Mc), that of H2C C-. and H3C-C- to 2
and 4 ppm, respectively, coinpared with the uncharged
0
groups. The chemical shift in the ion (CH&-W, compared
with t-butyl fluoridc, is 273 ppm (or 4090 cps), and that of
The absolute configuration at all the asymmetric ccntrcs was
determined by correlation with ( )-kaurene. The new pentacqclic skeleton is cyclokauranc ( I ) [2]. Cyclokaurnnolic acid
(2) was cited as an example or the new diterpenes.
[Karlsruher Chemische Gesellschaft
(Germany), June 27th, 19631
[VB 739/101 IE]
CB
the 13C-H coupling in H3C l3CH --CH3is 382 cps. This is
indicative of sp2 - hybridization of the positively - charged
carbon atom in the planar carbonium ions.
[Inorganic Chcmistry Colloquium at the Technische Hochschule Aachen (Germany), June 24th 19631 [VB 711/94 IE]
Gcrman version: Angew. Chem. 75, 800 (1963)
German version: Angew. Chem. 75, 940 (1963)
[ I ] Experimental work by 6./ / / / g e l , L. Lo&
J . M . Mellor, and
D.W. Tlicobuld.
[2] Note added September 26111, 1963: The name of the pentacyclic skeleton ( 1 ) has now hccn changed, at the suggestion of
Dr. K. Overtori (Glasgow), to /wc~lr~~lohanc.
629
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