The current-voltage characteristics of ultrasmall Josephson junctions sensitively depend on the electromagnetic environment of the junction. When the charging energy exceeds the Josephson coupling energy, the usual supercurrent at zero voltage is completely suppressed. However, for typical environmental impedances, which are small compared to the resistance quantum, stochastic Cooper-pair tunneling leads to a supercurrent peak at a small finite voltage which is proportional to the temperature and the low-frequency resistance of the external circuit. An analytic expression for the form of this universal peak, which is independent of the high-frequency behavior of the environment, is given. With increasing Josephson coupling the peak merges into the usual supercurrent of a Josephson junction. At larger voltages the Cooper-pair current depends on details of the environment. Current peaks are shown to result from resonances in the environmental impedance. Specifically, the case of an LC transmission line of finite length is discussed.
On the Stereasdective FormatMa of syn-and mtj-D€cacsrboayb The reactions of MFe(CO)3N0 (7, M = K) with @)-and (Z)Zbutenyl mesylate (E-1 and 2-1; R = CHh X = OS02CH3) lead stereoselectively to syn-and mti-dicarbonyl(l-methyl-q3-2-propeny1)nitrosyliron (syn-6 and antid), respectively. In a subsequent selective reaction with the anion of dimethyl malonate, these complexes afford [along with dimethyl (I -methyl-2-propenyl)malonate (4; R = CH,, Nu = CH(CO&H&J dimethyl@)-and (2)-2-butenylmalonate [E-3 and 2-3; R = CH,, Nu = cH(C02-CH3)& where the double-bond geometries of the educts are retained. Upon treatment with PPhp (ll), both, syn-6 and anti4 (latter with isornerkation), form the same crystalhe complex, syncarbonyl( 1 -methyl-q3-2-propyl)nitrosyl(triphe~ylp~osphine)-iron (12); its structure w&s determined by X-ray dfiraction.
On the Formation of Two Unwsual Muhinuelear Iron ComplexesThe reaction of KFe(C0hNO (1) with PhCOCl(2) afforded the dinuciear iron complex S; in the presence of PPh3 (12), the trinuclear complex 13 was formed. The structures of both compounds were determined by X-ray diffraction.Die Darstellung von stabilem Acetyldicarbonylnitrosyl(tripheny1phosphan)eisen sowie der Nachweis von instabilem Benzoyldicarbonylnitrosyl(tripheny1phosphan)eisen durch Reaktion von Natrium-tricarbonylnitrosylferrat mit Acetylchlorid bzw. Benzoylchlorid in Gegenwart von Triphenylphosphan sind schon lange bekannt').Beim Studium des Verhaltens von Kalium-tricarbonylnitrosylferrat (1) gegenuber Reagentien, die elektrophile Kohlenstoff-Atome enthalten, erhielten wir bei der Reaktion mit Benzoylchlorid (2) die bisher unbekannte Verbindung 8 in Form tiefvioletter Kristalle.
1,3-Dimethy1-2-mesitylcyclopentadien (5) wird auf zwei Wegen hergestellt. Das 'H-NMR-Spektrum des Cyclopentadienyl-Anions 3 zeigt eine Differenz der chemischen Verschiebungen zwischen den p -und o-Methylgruppensignalen A 6 = 0.25 ppm. Dieser im Vergleich zu Bimesityl (2b) ( A 6 = 0.47 ppm) und zum Tropylium-Ion 1 ( A 6 = 0.56 pprn) niedrige Wert wird mit dem EinfluB der hohen x-Elektronendichte im Anionfunfring auf die Methylgruppen durch den Raum erklart. Dafur wird im Bereich 1 bis 3 eine lineare Beziehung gefunden. Die Rdntgenstrukturanalyse des aus 3 erhaltenen Ferrocens 18 zeigt, daR die Mesityl-und Cyclopentadienyl-Ringe senkrecht aufeinander stehen.
Anisotropy Effects of Conjugated Cyclic Systems, V1)'H NMR Spectra of Mesityl Substituted Aromatic 6n Systems 1,3-Dimethyl-2-mesitylcyclopentadiene (5) has been synthesized in two routes. The 'H NMR spectrum of the cyclopentadienyl anion 3 shows a difference of chemical shift values of the p -and o-rnethyl groups of A 6 = 0.25 ppm. Compared with bimesityl (2b) (A6 = 0.47 ppm) and the tropylium ion 1 ( A 6 = 0.56 ppm) this is a small A 6 value. This is interpreted by the influence of the x electron density from the five-membered anion ring on the methyl groups through space. In the range 1 to 3 there is found a linear relationship for this influence. X-ray analysis of the ferrocene derivative 18 prepared from 3 confirms the perpendicular orientation of the mesityl and cyclopentadienyl rings.In einer fruheren Mitteilung ') konnte gezeigt werden, dal3 die Differenzen der chemischen Verschiebungen zwischen den 'H-NMR-Signalen der p -und o-Methylgruppen AS in mesitylsubstituierten 2,6-Dimethylbenzol-Derivaten 2 nur sehr wenig um den Wert des als Standard gewahlten Bimesityls (2b) (AS = 0.47 ppm) schwanken, wobei elektronenziehende Substituenten wie R = CN in 2a (AS = 0.52 ppm) zu hdheren und elektronenspendende Substituenten, z. B. R = OCH, in 2c (AS = 0.44 ppm), zu niedrigeren Werten fuhren.Da Substituenteneffekte auf den A6-Wert klein sind, ist es gestattet, diese AS-Werte als Kriterium fur den aromatischen Charakter mesitylsubstituierter cyclischer Systeme anzusehen. In diesem Zusammenhang war es von Interesse, den EinfluB von ganzen
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