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Ionization Energies of Silyl- and Alkyl-ethylenes.

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The structures of (2a). (2b), and (2d) were proved by mixed
melting points o r mixed chromatograms with authentic
samples and by comparison of the I R spectrar3.71.
Alkyl- and aryl-cyclopropenes are stable under the above
conditions, but o n longer irradiation, parlicularly in rhe
presence of sensitizers, are converted into tricyclohexanes [4,81.
Received: October l l t h , 1967
[Z 634 IEI
German version: Angew. Chem. 79, 1104 (1967)
["I Dr. H . Diirr
lnstitut fur Organische Chemie der Universitat
66 Saarbriicken 1 5 (Germany)
[ l ] Part IV of Photochemistry of Small Rings. - Part 111: H .
Diirr, Liebigs A n n . Chem., in press.
121 W. R. Bamford and T . S . Stevens, J. chem. SOC.(London)
1952, 4735.
[ 3 ] G . L. Closs, L. Gloss, and W. Boll, J. Amer. chem. SOC. 85,
3796 (1963).
[4] H. H. Stechl, Chem. Ber. 97, 2681 (1964).
[5] Diethylene g!ycol dimethyl ether.
[6] W . G. Dauben and F. G. Wiley, 3. Amer. chem. SOC.84, 1498
[7] R . Breslow and H . W . Chang, J. Amer. chem. SOC.83, 2367
(1961); R. Breslow and P . Dowd, ibid. 85, 2129 (1963).
[8] H. Diirr, Tetrahedron Letters 1967, 1649.
Organic Compounds in Fossil Plants
(Equisetum; Horsetails) [*I
By H . Knoclte and G. Ourissun [*I
Chemotaxonomic classification of fossil plants would be
particularly interesting since it could be carried out on mutilated and incomplete specimens, and because conclusions
could be drawn about the history of the fossils from comparison of the constituents of fossil and fresh plants.
We have begun experiments designed to isolate organic compounds, in particular hydrocarbons, from fossil plants from
the bunter sandstone of the Northern Vosges (Trias, 2 x 108
years old) and to compare them with the compounds in
present-day plants. Of the fossils available to us a horsetail
Equisetum brongniarti I21 was especially interesting because
numerous Equisefum species still grow today. The stems of
the plants were approximately 30 mm in diameter. I n addition, horsetails have few parasites 131, which diminishes the
danger of the compounds found originating from foreign
organisms. Great attention was paid t o purity during the
collection, and contamination during working up was excluded by control experiments. The Equisetum described
here came from a clay inclusion in the bunter sandstone Of
the Northern Vosges (Hangvillier, Moselle).
400 g of dried rock containing ca. 20% of fossil plants (further separation from the rock is rather difficult and unnecessary since the surrounding material contains very little
organic material [41) were ground and extracted with 400 ml
of a benzenej'methanol mixture (3: 1 v/v) using a n ultrasonic
technique (25 kHz). Centrifugation, decantation, and removal
of the solvent by distillation gave 3 mg of residue, which was
desulfurized in a small column by 100 mg of active copper
and then separated on 2 g of silica gel (Merck, 0.05-0.2 mm).
Elution with 50 ml of petroleum ether gave the hydrocarbon
fraction (ca. 0.5 mg). The gas chromatogram (Fig. l a ) showed
four main components in the ratio 1 :I : 2.4: 2151.
50 g of fresh, dried Eqzrisetum sylvnticum (wood horsetail) was extracted with 500 ml of benzene (ultrasonically).
The hydrocarbon fraction (18 mg) was isolated from theextract
by column chromatography. The gas chromatogram of this
fraction (Fig. l b ) showed the same four main components
in almost the same proportions, namely, 1 : 1:2.4: 1.3 [ * * I .
The products were identified as the normal hydrocarbons
n-C23H48, n-Cz5Hsz, n-Cz7H56, and n-Cz9Hso by their gaschromatographic retention times [61, mass spectra, and
inclusion in Linde molecular sieves ( 5 p\, 6 h in boiling isooctane). The extract of the fresh plant does not contain the
numerous minor components of the fossil plant.
In this work the same compounds have been isolated for the
first time from a living and a fossil plant and it has been
proved that hydrocarbons can remain unchanged in a fossil
for 200 million years.
Received: October 13th, 1967
[ Z 636 IE]
German version: Angew. Chem. 79, 1107 (1967)
[ * ] Prof. G. Ourisson and Dr. H. Knoche
Universite d e Strasbourg, Institut de Chimie,
Laboratoire attache au C.N.R.S.,
1, rue Blaise Pascal
Strasbourg (France)
[**I Note added in proof: K . Stransky, M . Streibl, and V. Hemiit,
Collect. czechoslov. chem. Commun. 32, 3213 (1967), have
recently found the ratio of alkanes n-CP3: n-Czs:n-Cz7:n-C29 to
be approximately I : I : 3 : 0 . 5 in the wax of fresh Eyuisetum
pcilustre L.
[ I ] Part I. - This work forms part of the research program
D.G.R.S.T. NO. 64-FR-058. -- We thank Messrs. L. Grauvogel
and J.-C. Gail for help in collection of the fossils, and Dr. Vetter,
Hoffman-La Roche, Basel, for determination of the mass spectra.
[2] W. P. Schimper and A . Mougeot: Monographie des piantes
fossiles du gres bigarre der chaine des Vosges. Wilhelm Engelmann, Leipzig 1844.
[3] R. Hegnauer: Chemotaxonomie der Pflanzen. Birkhiiuser,
Basel, Stuttgart 1962, Vol. I.
[4] R. Brandt and G. Ourisson, unpublished work.
[SI Conditions: Perkin-Elmer gas chromatograph 226, 1.5')/, of
SE-30 on Aeropack 30, SO/lOO mesh, 1.80 long, 3 mm in diameter,
program 6.25 "C/min, 100-290 "C, 30 ml of He per min.
161 Perkin-Elmer gas chromatograph 226, capillary column
0.025 mm, 50 m, SE-30, 240 "C, 1.6 mol of He per min; retention
times: benzene 3.9 min., n-Cz, 9.3 min, n-C25 13.5 min, n-CZ7
31 min, n-C29 33.8 min.
Ionization Energies-of Silyl- and
Alkyl-ethylenes [**I
By H. Bock and H. SeidIc*I
Fig. 1 . Gas chromatograms IS] of the hydrocarbon fractions from (a)
fossil and (b) fresh Eqvisefum.
Angew. Chem. internat. Edit. 1 VoI. 6 (1967)
No. I 2
The differing properties of simple x-electron systems containing R3Si- and R3C-substituents can be considered as being
due t o the different inductive polarization (+Is~R, >
+IcR,) and additional conjugative back-donation of electrons Sid + C,. The relative energy changes of the highest
occupied and lowest unoccupied molecular orbitals caused
by interaction with the substituents can be measured individually be means of e.g. half-wave potentials [I], electron spin
densities [21, or charge-transfer band maxima [31, while the
resulting total energy differences can be determined from the
corresponding transitions in the electronic spectrar2.31. Of
the cross-conjugated [I], cyclic [2,31, and linear n-electron
systems containing R3Si-groups, ethylene derivalives were
the first for which we were able t o determine ionization
energies by mass spectroscopy (41 and thence t o obtain, by
means of the Koopman theorem [51, direct information about
the highest occupied (x)-levels “51.
The hitherto unknown [71 tris(trimethylsilyl)ethylene (2) can
be prepared as shown :
-R3St -
+ HSiClzR
[*] Priv.-Doz. Dr. H. Bock and Dip1.-Chem. H. Seidl
and applying the usual model of the Si-Cs,2 bond this
provides further evidence [1-31 in favor of a conjugative
Sid + C, electron back-donation. A minimum value for the
+ I s ~ R , effect follows from the ionization energy of t-butylethylene which is 0.8 eV higher than that of l-trimethylsilyl2-propene where the P-situated R3Si group is separated
from the x-electron system by a tetrahedral C atom.
The d-orbital interactions demonstrated by the ionization
energies for the ground state of silylethylenes were used
previously t o explain why the N M R signals of the ethylene
protons are shifted to lower field in comparison with the
alkyl derivatives 191 and why the C = C stretching frequencies
are lowered [lo]. In this connection, extreme differences are
shown by the values for tris(trimethylsily1)- and trimethylethylenes, where a difference of 5000 cm-1 = 14 kcal/mole in
the x + x* excitation energies also indicates considerable
x*/d splitting 1111. Smaller, but similar, differences between
the properties of silyl- and alkyl-polyenes and -poIyynes 1111
confirm the d-orbital effects for silyl substituted linear x electron systems.
[ Z 635 IE]
Received: October 13th, 1967
German version: Angew. Chem. 79, 1106 (1967)
60 mmoles of dichloro(methy1)silane is added dropwise and
slowly to an equimolar amount of bis(trimethy1silyl)acetylene
to which has been added 0.3 ml of a 0.1 N solution of HzPtC16
in 2-propanol. After 20 hours’ boiling under reflux, distillation affords 1 3 % of ( I ) , b.p. 57-60°C/0.5 mm, which
affords 47% of (2), b.p. 43--45 OC/O.5 mm, by a Grignard
reaction. The product is purified by gas chromatography
(SE-30 column). The 1H-NMR-spectrum contains three
singlets in the ratio 1 :18:9 at T = 2.67, 9.86, and 9.91; the
C = C stretching frequency appears at 1499 cm-I. Comparison
with the corresponding data for trimethyl ethylene‘s]
(IH-NMR signal of the ethylene proton: 4 . 8 3 ~ ; C = C
stretching frequency 1667 cm-1) illustrates t o what extent
characteristic properties of the ground state of simple R3Siand R3C-substituted x-electron systems may differ.
Institut fur Anorganische Chemie der Universitat
Meiserstr. 1
8 Miinchen 2 (Germany)
[**I Part IV of d-Orbital Effects in x-Electron Systems Containing Silicon Substituents. - Part 111 [31.
[l] H. Bock and H . Alr, Angew. Chem. 79, 941 (1967); Angew.
Chem. internat. Edit. 6 , 932 (1967).
[2] H . Alt, H . Bock, F. Gerson, and J . Heinzer, Angew. Chem.
79, 933 (1967); Angew. Chem. internat. Edit. 6 , 941 (1967).
[3] H. Bock and H. All, Angew. Chem. 79, 934 (1967); Angew.
Chem. internat. Edit. 6, 942 (1967).
[4] We thank Mr. M . Fochler for measuring the appearance
potentials. According to R . I . Reed (Ion Production by Electron
Impact. Academic Press, London 1962), the “vertical” ionization
energies determined in this way for alkylated ethylenes are in
good agreement with the “adiabatic” counterparts. In the series
studied, the individual values were scattered by at most 50.04 eV.
(51 T. Koopmans: Physica. Nijhoff, DenHaag 1934, Vol. I, p. 704.
[6] M . 5.Robin, R. R. Hart, and N . A. Kuebler, J. chem. Physics
44, 1803 (1966).
I71 R . West and G. R . Husk synthesized the compound by a
similar route (personal communication at the IUPAC Syrnposium on Organometallic Chemistry, Miinchen (Germany) 1967).
[S] Possibly, non-bonding interactions between the bulky cis
(CH&Si-groups play a part. It is impossible to build a StuartBriegleb model for a tris(t-butyl)ethylene, in the model of the
tris(trimethylsily1) derivate (dR,Si-c
dR3C-c) rotation of the
cis-R3Si groups 1s sterically hindered.
[91 R . T . Hobgood, J . H. Goldstein, and G . S. Reddy, J. chem.
Physics 35, 2038 (1961); cf. also R. Summit, J. J. Eisch, J. T.
Trainor, and M . T . Rogers, J. physic. Chem. 67, 2362 (1963).
[lo] J. Knizek, M . Horak, and V. Chvalovsky, Coll. czechoslov.
chem. Commun. 28, 3097 (1963).
[ l l j H. Bock and H. Seidl, unpublished work.
Cyclization of Acid Chlorides by
Polyphosphoric Acid
Fig. 1. Ionization energies (IE) of silyl- and alkyl-ethylenes.
The diagram (Fig. 1) for the highest occupied (x)-molecular
orbitas 161 of silyl- and alkyl-ethylenes permits the following
conclusions : (+I)-Substituents such as R3Si- and R3Cgroups lower the ionization energy of the ethylene x-electron
system, corresponding to a rise of the x-level, which for
the silyl derivatives CnH4-n(SiR3)n is linearly proportional,
within a good approximation, to the number of substituents.
The effect of the R3Si-groups is, however, in all cases less
than required for inductive polarization ( I s ~ R>~ +IcRJ,
By A . Bhati and
We have cyclized arylalkanecarbonyl chlorides ( I ) , namely,
4-phenylbutyryl, 5-phenylvaleryl, 4-(2-chloro-5-methoxyphenyl)butyryl, and 4-(5-chloro-2-methoxyphenyl)butyryl
chloride, with polyphosphoric acid and thus obtained the
cyclic ketones (2) in excellent yield.
Angew. Chem. internat. Edit. f Vol. 6 (1967) 1 No. 12
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alkyl, ethylene, sily, energies, ionization
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