Abstract-The 13C NMR spectra of nearly 100 rnonoterpenes show thatthey ar every useful for the characterisation of these compounds. This method is especially valuable for the elucidation of stereochemical problems. With the exception of a few cases the observed chemical shifts follow the common rules. The problems with measurements using shift reagents are discussed.

Edited by Ruma BanerjeeThe enzymes of the thiosulfate dehydrogenase (TsdA) family are wide-spread diheme c-type cytochromes. Here, redox carriers were studied mediating the flow of electrons arising from thiosulfate oxidation into respiratory or photosynthetic electron chains. In a number of organisms, including Thiomonas intermedia and Sideroxydans lithotrophicus, the tsdA gene is immediately preceded by tsdB encoding for another diheme cytochrome. Spectrophotometric experiments in combination with enzymatic assays in solution showed that TsdB acts as an effective electron acceptor of TsdA in vitro when TsdA and TsdB originate from the same source organism. Although TsdA covers a range from ؊300 to ؉150 mV, TsdB is redox active between ؊100 and ؉300 mV, thus enabling electron transfer between these hemoproteins. The three-dimensional structure of the TsdB-TsdA fusion protein from the purple sulfur bacterium Marichromatium purpuratum was solved by X-ray crystallography to 2.75 Å resolution providing insights into internal electron transfer. In the oxidized state, this tetraheme cytochrome c contains three hemes with axial His/Met ligation, whereas heme 3 exhibits the His/Cys coordination typical for TsdA active sites. Interestingly, thiosulfate is covalently bound to Cys 330 on heme 3. In several bacteria, including Allochromatium vinosum, TsdB is not present, precluding a general and essential role for electron flow. Both AvTsdA and the MpTsdBA fusion react efficiently in vitro with high potential iron-sulfur protein from A. vinosum (E m ؉350 mV). High potential ironsulfur protein not only acts as direct electron donor to the reaction center in anoxygenic phototrophs but can also be involved in aerobic respiratory chains.

Trichlorosilanes RSiCl3 (R = t-Bu, Mes, Cp*, Is, OAr) reacted with a 4-fold excess of lithium phosphanide ArPHLi (Ar = 2,4,6-tBu3C6H2) to form 1,3-diphospha-2-silaallylic complexes 3a−f. From the latter, the corresponding free allylic anions could be liberated by complexation of the lithium cation with [15]-crown-[5], as could be established on the basis of NMR spectra and X-ray structures. In addition, the bonding in the Li complexes was further investigated using ab initio calculations of double-ξ quality. The influence of cation solvation on the complex geometry was explored as well. The chemical reactivity of 1,3-diphospha-2-silaallylic anions with electrophiles (E = H+, ClPR‘R‘‘) was investigated. 1,3-Diphospha-2-silapropenes 4a−d and 1,3,4-triphospha-2-silabutenes-(1) 5a−e and 6a were prepared.

electron-pair model['*] will operate in a way analogous to that suggested for the Cu-0 superconductors: concerted inplane M-0 breathing motions can be established via local Jahn-Teller instabilities. Our band calculations on 1 with two Bi,O, layers sandwiching it show no significant contribution of the Bi,O, layers to the t,,-block bands. Our calculations on 2 and 3 without the embedded atoms, B, show that the essential features of the t,,-block bands remain unaltered. Small coupling exists between the xz and yz bands via the out-of-plane oxygen atoms that bridge the MO, layers, while the xy bands are not coupled via the out-of-plane oxygen atoms. The x2 -yz bands of the Cu-0 superconductors behave identically.['* '

Ein stabiles, delokalisiertes 3p‐π‐Bindungssystem liegt im Lithiumsalz 1 der Titelverbindung vor. 1 ist überraschend einfach zugänglich. Die Bildung des Heteroallylsystems wird durch die η2‐Koordination des Lithiums sowie die kurzen P‐Si‐Bindungen belegt. Mit H2O und mit Me3SiCl reagiert 1 zu Spezies mit P = Si‐Bindung (Aryl = 2,4,6‐tBu3C6H2).

The title anion, the first example of a stable delocalized 3p(π) bonding system, is prepared as its Li salt (V) according to the scheme.

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