Conformational changes in cyclic and linear chains triggered by increasing chain stiffness are explored using MC simulations. The transition to the rigid strained objects is continuous and steeper for cycles. Circular macromolecules of contour length equal to ≈5 persistence lengths are characterized as rigid strained objects with a lowered spatial dimensionality. The coil regime is almost omitted in the static structure factor already for semiflexible chains of both architectures and the flattening of stiffer cycles is evidenced by oscillations superimposed on the rod‐like behavior of corresponding linear chains. The orientational correlation function shows qualitative difference in behavior of cyclic and linear chains.
Preparation of Cyclophosphates, Cyclophosphatophosphonates, Diphosphonates, and Di-phosphites in Urea Melts Ammonium cyclotriphosphate (NH4)P3O9, ammonium cyclotetraphosphate [PIV? PIV ? O? ]2, ammonium cyclotriphosphatophosphonates Ammonium organyldiphosphonates And ammonium diphosphites are prepared in high yields on heating acidic phosphates, phosphonates, and phosphites in urea or urea/ammonium nitrate melts. The mechanism of the dehydration of phosphorus compounds containing POH groups in molten urea is discussed. 相似文献
A powerful fluoride trap : The extremely Lewis acidic silyl cation [Et3Si]+ is an active catalyst for the hydrodefluorination of fluoroalkyl groups at room temperature (see example). The carborane anion [CHB11H5Cl6]? plays an essential role in the catalytic cycle as a weakly coordinating anion that stabilizes cationic intermediates.
“My biggest motivation is to see my students′ progress. When I was eighteen I wanted to be unexcitingly, a chemist…︁!” This and more about Stefan Mecking can be found on page 3213.
Sleeping beauty? Is the scientific community about to kiss awake iron catalysis, a topic that has been dormant for decades? A recent study on a user‐friendly direct cross‐coupling reaction of alkyl and aryl halides constitutes an important step toward this end through the integration of two different iron‐catalyzed elementary steps into a practical one‐pot procedure.
Bi? O chemistry : A direct regioselective route to bismuth bis(amino)naphthalene compounds, incorporating Bi? O and Bi? C bonds is described, in which an amide precursor is treated with aldehydes, ketones, alkenes, and alkynes, leading to insertion into the Bi? NMe2 bond.
?The biggest challenge facing scientists is finding a way to make clean energy. If I could have dinner with three famous scientists from history, they would be Marie Curie, Dmitri Mendeleev, and Henri Moissan. …?“ This and more about Véronique Gouverneur can be found on page 3559.
B‐hive? A family of crystalline materials analogous to porous AlPO4 but based on boron imidazolate frameworks (BIFs) can be formed by the crosslinking of various presynthesized boron imidazolates with monovalent cations (Li+ and Cu+, see picture). This synthetic method is capable of generating a large variety of open frameworks, ranging from the four‐connected zeolitic sodalite type to the three‐connected chiral (10,3)‐a type.
Ferrous efficiency : New achiral and chiral iron complexes containing P‐N‐N‐P diiminodiphosphine ligands display high activity—and in the case of the catalyst shown, high enantioselectivity—in the catalytic transfer hydrogenation of ketones. This is an important step in the journey to replace precious and toxic platinum metal catalysts with cheap and environmentally friendly iron compounds.
A breakthrough in the asymmetric hydroboration of notoriously difficult 1,1‐disubstituted alkenes using a new family of highly effective hydroboration reagents is described (see scheme). The intermediate boranes can be oxidized to alcohols or used in Suzuki–Miyaura cross‐coupling reactions.
Iron man or weakling? Ligand‐field strengths are conveniently expressed by the empirical spectrochemical series. Although cyanide has been deeply entrenched as a strong‐field ligand, a couple of recent examples cast doubt toward the position of this ligand, namely the high‐spin (S=2) states of [CrII(CN)5]3? and [FeII(tpp)(CN)]?. tpp=meso‐tetraphenylporphinate.
Why beat about the bush? An operationally simple and mild reaction based on the direct fixation of 11CO2 with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) has been developed for the synthesis of 11C‐labeled carbamates at 75 °C within 10 minutes in radiochemical yields above 70 % (see scheme). This strategy should be immediately useful for the construction of new radiotracers for positron emission tomography and other applications.
A spin‐crossover cluster with the {FeII4O4} core structure is presented by D. Y. Wu, O. Sato et al. in their Communication on page 1475 ff. The cluster is synthesized by self‐assembly and shows an abrupt spin transition, giving two high‐spin and two low‐spin states. It exhibits complete light‐induced excited spin‐state trapping effects. Importantly, synergy effects between the magnetic interaction and spin transition operate in the cluster.
Three of a kind : Vicinal tricarbonyl compounds undergo C? C cleavage mediated by ferric ions (see scheme). The observed cleavage of ninhydrin and dehydroascorbic acid has relevance for amino acid detection and the metabolism of vitamin C.
