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Biosynthesis of Aromatic Systems.

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Optical Behavior of Solutions of Sodium in
Ammonia at High Pressures
Solutions of N a in NH3 have a lower density and a greater
compressibility than pure ammonia. This is attributed to
the solvated electrons that are formed o n dissociation of the
Na (Na + Na+ ecOl).The solvated electrons are situated
inside cages formed of NH3 molecules. The apparent molar
volume of the dissolved Na (60 to 70 ml/mole; cf. pure Na
23 ml/mole) gives a value of 3.25 A for the radius of the
solvated electrons.
The dilute solutions are deep blue (absorption maximum at
1.5 EL; maximal extinction coefficient 4x104 1 mole-1 cm-1)
owing to strong light absorption in the red to near infrared
spectral region. The absorption is attributed to transition of
the electrons from the Is to the 2p state in a hydrogen-like
potential, paralleling the light absorption of F-centers
(electrons at anion sites in ionic crystals). The transition
energy is, to a first approximation (square well potential),
inversely proportional to the square of the radius of the cage
containing the electrons. Quantum mechanical calculation using the radius given above for the solvated electron is in agreement with the transition energy found
The increase in compressibility of the solutions suggests that
solvated electrons are more compressible than pure ammonia.
Because of the relation between the radius of the solvated
electrons and the energy of the electron transition it should
be possible to estimate their compressibility from the increase in shift of the absorption maximum towards shorter
wavelengths with increasing pressure.
The absorption spectra of dilute Na-NH3 solutions at
pressure up to 2000 atm and at temperatures -60 and t 2 0 OC
were studied by using a high-pressure cell. Owing to the
strong absorption of the solutions the light path was kept
below 10-2 cm.
The results of these investigations confirm the hypotheses:
compression of the solvated electron by pressure shifts the
absorption maximum towards shorter wavelengths (1000 A/
1000 atm); o n the other hand, increase in temperature shifts
the absorption maximum towards longer wavelengths
(1000 &'40 "C).The latter shift can be interpreted as due to
thermal expansion of the solvated electrons.
These measurements lead to values of the compressibility
(6.5~10-5atm-1) and thermal expansion (3.0~10-2deg-1) of
the solvated electrons that are greater than those of pure
ammonia (4.0~10-5atm-1 and 1 ~ 9 . 1 0 - 2deg-1. respectively).
Solvated electrons thus contrast with normal solvated ions,
whose compressibilities and thermal expansions are smaller
than those of the solvating medium.
[VB 65 IE]
Lecture at Marburg (Germany) on January 20th, 1967
German version: Angew. Chem. 79, 585 (1967)
[ * ] Doz. Dr. U. Schindewolf
Institut fur Kernverfahrenstechnik
der Technischen Hochschule
75 Karlsruhe (Germany)
Biosynthesis of Aromatic Systems
vegetable origin that both routes can contribute together to
the formation of aromatic natural products.
More than half of the 14 stilbene derivatives that are now
known as constituents of higher plants have been studied in
regard to their biosynthesis [3]. The syntheses proceed along
analogous routes in very different types of plant, namely,
condensation of a cinnamic acid (1) with three acetate units,
leading, o n loss of a carboxyl group, to 3,5-dihydroxystilbene
(pinosylvin) (2). Hydroxylated cinnamic acids Cp-coumaric,
2,4-dihydroxycinnamic, caffeic, and isoferulic acid) yield the
correspondingly substituted 3,5-dihydroxystilbenes resveratrole (3,5,4'-trihydroxy-), oxyresveratrole (3,5,2',4'-tetrahydroxy-), piceatannol (3,5,3',4'-tetrahydroxy-), and rhapontigenin (3,5,3'-trihydroxy-4'-methoxy-stilbene).
Biosynthesis of hydrangeic acid ( 3 ) and hydrangenol ( 4 )
proceeds without loss of a carboxyl group but with intermediate reduction.
Benzoic acids, which are widely distributed in higher plants,
are not formed, as previously assumed, by aromatization of
dehydroshikimic acid or of shikimic acid, but by degradation
of cinnamic acids [41. In the biosynthesis of hydroxylated
benzoic acids the substitution pattern can be determined at
the cinnamic acid stage since conversions such as ferulic
acid + vanillic acid, and p-coumaric acid + p-hydroxybenzoic acid, are known. On the other hand, for biosynthesis
of gentisic acid the route cinnamic acid + benzoic acid +
salicylic acid + gentisic acid has been demonstrated, i.e. in
some cases hydroxylation occurs only at the benzoic acid
stage 151.
[VB 67 IEI
Lecture at Hamburg (Germany) on February 24th, 1967
German version: Angew. Chem. 79, 586 (1967)
[ * ] Doz. Dr. G. Billek
Behringstr. 154
2 Hamburg 50 (Germany)
[ l ] A. J . Birch, Fortschr. Chem. org. Naturst. 14, 186 (1957);
F. Lynen and M . Tadu, Angew. Chem. 73, 513 (1961).
[2] D. B. Sprinson, Adv. Carbohydrate Chem. 15, 235 (1960).
[3] G. Billek and H . Kindl, Mh. Chem. 92, 493 (1961); 93, 814
(1962); G. Billek and W. Ziegler, ibid. 93, 1430 (1962); G. Billek
and A . Schimpl, ibid. 93, 1457 (1962).
[4] H. Kindl and G. Billek, Osterr. Chem.-Ztg. 63, 290 (1962);
Mh. Chem. 95, 1044 (1964).
[5] G. Billek and F. P . Schmook, Mh. Chem., in press.
Chemistry of Sulfur Ylides
By H . Konig[*I
By G. Bilfek [*I
Aromatic natural products are formed almost exclusively
by (i) condensation of acetate and malonate units (polyacetate rule [I]) o r (ii) through intermediate stages of carbohydrate metabolism, by way of shikimic, chorismic, and
prephenic acid (shikimic acid route[21). Examples of the
latter are the aromatic amino acids phenylalanine and
tyrosine and their deamination products cinnamic and
p-coumaric acid. It has been found for stilbenes of
Angew. Chem. internot. Edit. 1 V d 6 (1967) No. 6
Whereas cinnamonitrile, like a,@-unsaturated ketones, is
converted into phenylcyclopropanecarbonitrileby dimethyloxosulfonium methylide ( I ) , cinnamanilide affords only a
little of the cyclopropane derivative along with much 1,3diphenylpyrrolidone. The nature of by-products from other
a,@-unsaturated amides permits conclusions to be drawn
about the reaction mechanism. Reaction of a carbonyl o r
imine group with ( I ) occurs with methylene transfer and
formation of heterocycles containing three-membered rings.
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system, aromatic, biosynthesis
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