ther developed with propan-1-ol/conc. ammoniaiwater (6: 3: 1). After drying, the lower fluorescence-quenching ATP zone was removed and the silica gel was eluted with 25 ml of 0.05 M Tris buffer (PH = 7.55). The yields of ATP determined enzymically [71 and referred t o the A D P used were: o n oxidation with bromine 6.0 and 6.8%; on oxidation with tetrabromo-o-benzoquinone 9.5 %; without oxidizing agent 0.0 %; and without acetyldurohydroquinone monoacetate 0.0%.

No abstract

High-resolution 13C NMR spectra obtained using cryogenic CPMAS methodology at temperatures as low as 10 K suggest that the structure of 11,l l-dimethyl-l,6-methano[l0]annulene is nonclassical.The problem of valence tautomerism of 1,6-methano[ 101-annulene (1aIIIa)l and its derivatives with two bridge substituents, in particular 11,l l-dimethyl-1,6-methano[lO]annulene (DIM, Ib/IIb)? has been of considerable interest for a long time. As shown in Figure 1 these molecules either exist as an interconverting mixture of an aromatic form (I) and a bisnorcaradiene form (11) separated by an energy barrier (Figure ldf) or adopt an intermediate nonclassical structure between the extremes 1 and 11 (Figure la-c). Solution 13C NMR studies of a variety of 11,ll-disubstituted 1,6-methano[lO]annulenes exhibited a surprisingly large range for the chemical shift of the central carbon atoms 1 and 6, 124 ppm =. d1,6 > 40 ppm,where derivatives with a shift at the low-field value were assigned to form I.las2v3 Furthermore, for some of these molecules, a temperature dependence of d1,6 was found and interpreted in terms of a fast tautomerism between the two forms2 Similar conclusions were reached in a recent variabletemperature 13C CPMAS NMR study of DIM carried out at temperatures down to 140 K.3 Theoretical studies also favor interconversion over a barriere4 In contrast, room-temperature crystal structures of several 1,6-methano[ 101annulenes showed C1C6 distances varying between 1.54 and 2.27 A, indicating nonclassical structures between the two extremes I and IL5 In this we report the results of 13C CPMAS NMR experiments on DIM at very low temperatures (100-10 K) which support a nonclassical structure.A selection of the spectra, obtained at 1.4 T using an apparatus described previously,6 are shown in Figure 2. The two lines marked A and B at 80 and 74 ppm, respectively, have been assigned3 to the equivalent carbon atoms C1 and c 6 of molecules in two nonequivalent sites, A and B, in the asymmetric unit, exhibiting slightly different Clc6 distances of 1.836 and 1.780 A.7 The position of line A remains remarkably constant over the entire temperature range (10 K to ambient), a phenomenon which at first sight is consistent3 with a degenerate rearrangement between forms I and I1 characterized by an equilibrium constant K -1. On the other hand, between room temperature and 140 K, the position of line B shifts slightly to higher fieldas t Permanent address:

No abstract

Für die „Pyrazolone”︁ wird eine einheitliche und logische Nomenklatur empfohlen, wobei alle N‐substituierten „Pyrazolone”︁ als Derivate der vier praktisch bedeutsamen Tautomeren des Grundkörpers, d.h. des 3‐Hydroxy‐pyrazols 1, Delta;4‐Pyrazolinons‐(3) 2, Δ2‐Pyrazolinons‐(5) 3 und 5‐Hydroxy‐pyrazols 4 aufgefaßt werden. Die „Pyrazolone”︁ sollten in Zukunft nach der tautomeren Form benannt werden, die allgemein bzw. in verdünnter, indifferenter Lösung bevorzugt vorliegt. Basierend auf kritisch eingeschätzten Literaturangaben über C‐substituierte und eigenen Untersuchungen über C‐unsubstituierte (R′ = R″ = H) „Pyrazolone”︁ wird in Abschn. 1 die Tautomerie der 3‐Hydroxy‐pyrazole 1 sowie der 1‐substituierten 3‐Hydroxy‐pyrazole 6 und in Abschn. 2 die Tautomerie der 1‐substituierten Δ2‐Pyrazolinone‐(5) 9 behandelt. Bei den Δ2‐Pyrazolinonen‐(5) 9 ist die Lage des tautomeren Gleichgewichts stärker vom Lösungsmittel, von der Konzentration und von den Substituenten R′ und R″ abhängig als bei den 3‐Hydroxy‐pyrazolen. Die Tautomerie der „Arylazo‐Derivate”︁ von „Pyrazolonen”︁ wird in Abschn. 3 diskutiert. In indifferenten Lösungsmitteln existieren sie als 4‐Arylazo‐3‐hydroxy‐pyrazole 21 bzw. als 4‐Arylhydrazono‐Δ2‐pyrazolinone‐(5) 26. Die „Imino‐pyrazoline”︁ (Abschn. 4) sind auf Grund der IR‐ und 1H‐NMR‐Daten als 3‐Amino‐ bzw. 5‐Amino‐pyrazole zu bezeichnen. An zahlreichen Beispielen wird die Erhöhung ihrer vicinalen H, H‐Kopplungskonstanten durch Elektronenakzeptor‐Substituenten am Ring‐N demonstriert.