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Electron Spin Resonance Studies of Bridged Annulenes.

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tubes, connected directly to the cell, serves for production
of free radicals.
Using such a spectrometer, Winnewisser, Sustry, and GurdyL2l first obtained the millemeter spectrum of sulfur monoxide (electron ground state 3C) in the gas discharge products
of SO2 and studied the magnetic properties of the radicalf31.
In the gas discharge product of H2S the relatively unstable
H& is formed from the SH radical by secondary reactions [41,
similarly to the production of H202 from OH radicals.
Formation of disulfane was proved by the rotational spectrum
in the millimeter region. The disulfane rotational spectrum is
the first 1-type spectrum of an almost symmetrical top
with x = -0.999985. This shows that the dipole moment is
perpendicular to the symmetry axis of the inertia tensor and
parallel to the twofold symmetry axis, thus proving the chain
structure of HSSH with C2 symmetry. Analysis of the millimeter spectrum I51 and electron-diffraction measurements f61
yielded the preliminary structure ( I ) for disulfane.
Electron Spin Resonance Studies of Bridged
By F. Gerson [*I
A model of a ten- or fourteen-membered Tc-electron perimeter
can be used for interpretation of the ESR spectra of radical
ions of the bridged annulenes ( I ) to ( 4 ) " 1 .
dlSSI=2.055 8
0 =90"36'
Fulminic acid is another unstable molecule whose structure
in the free gaseous state was hitherto unknown. Beck and
FeZdl[71 proved that it has the nitrile oxide form by means
of its IR spectrum. The microwave spectrum between 10000
and 50000 MHz indicates a linear molecule [81. Measurement
of the various isotope combinations showed the atomic
bonding HCNO and the preliminary structural parameters
indicated in formula (2).
The lowest antibonding (+a) and the highest bonding orbita
(+b) of the two perimeters are twofold degenerate. They can
be classified as 0% and +a-, and as +b+ and qb-, respectively.
Here plus denotes symmetrical and minus antisymmetrical
with respect to a plane that passes through two opposed centres in the perimeter and is perpendicular to the plane of the
perimeter. Bridging of the system results in lifting of the
degeneracy of +% and
on the one hand and of +b+ and
+b- on the other.
In the radical anions of the bridged [lO]annulenes ( I ) and (3)
the unpaired electron occupies the antisymmetrical orbital
+a-, which thus lies lower than
However, in the radical
anions of the bridged [14]annulenes (2) and (4) the unpaired electron is in the symmetrical orbital +a+. which is
here more stable than +a-.
In the radical cation, which can also be prepared from compound (4), there is a n unpaired electron in the symmetrical +b+ orbital, which thus has a higher energy than
Lecture at Kiel (Germany) on February ZOth, 1967
[VB 76 IEl
German version: Angew. Chem. 79, 727 (1967)
[*I Dr. M. Winnewisser
Technische Hochschule
Hertzstr. 16, Bau 35 I1
75 Karlsruhe (Germany)
111 R . Kewley, K . V. L. N . Sastry, M . Winnewisser, and W . Gordy,
J. chern. Physics 39, 2856 (1963).
[2] M . Winnewisser, K. V. L. N . Sastry, and W . Gordy, Bull.
Amer. physic. SOC.9, 488 (1964).
[3] M. Winnewisser, K . V . L. N . Sastry, R . L. Cook, and W . Gordy, J. chem. Physics 41, 1687 (1964).
[4] G. Winnewisser, M. Winnewisser, and W . Gordy, Bull. Arner.
physic. SOC.11, 312 (1966).
[5] G. Winnewisser, M. Winnewisser, and W . Gordy, unpublished.
[6] M . Winnewisser and J . Haase, unpublished.
I71 W . Beck and K. Feldl, Angew. Chem. 78, 746 (1966); Angew.
Chern. internat. Edit. 5 , 722 (1966).
[8] M . Winnewisser and H. K. Bodenseh, unpublished.
Angew. Chem. internat. Edit. 1 Vul. 6 (1961) / No. 8
These results permit conclusions to be drawn about the
nature and direction of the effect exerted by the bridges on
the ir-electron systems in compounds ( I ) to (4). Considered
in conjunction with the geometry of the compounds, they
lead to the following conclusions: In ( I ) and (2) the effect
of CH2, 0, and N bridges is mainly inductive and electronrepelling. In (4), however, this effect may perhaps be accompanied by hyperconjugation between the cr-electrons of
the butane bridges and the x-electrons of the perimeter.
Finally, in (3) the mesomeric and electron-donating effect
of the central nitrogen atom plays the most important part.
Lecture at Marburg on April 21st, 1967
[VB 78 IE1
German version: Angew. Chem. 79, 693 (1967)
[*] Doz. Dr. F. Gerson
Laboratoriurn fur Organische Chemie
Universitgtsstrasse 6
CH-8006 Ziirich (Switzerland)
[I] Cf. also F. Gerson, E. Heilbronner, N . Joop, and H . Zimmermann, Helv. chim. Acta 46, 1940 (1963); F. Gerson and J. D. W.
van Voorst, ibid. 46, 2257 (1963); F. Gerson, E. Heilbronner, and
V. Boekelheide, ibid. 47, 1123 (1964); F. Gerson, E. Heilbronner,
W . A. Boll, and E. Vogel, ibid. 48, 1494 (1965); F. Gerson:
Hochauflosende ESR-Spektroskopie, dargestellt anhand aromatischer Radikal-Ionen, Verlag Chemie, Weinheim 1967, in
press, Chapter 2, Section 5.
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spina, annulene, bridge, electro, resonance, studies
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