110 research outputs found
Fragmentation of a dioxolanyl radical via nonstatistical reaction dynamics: characterization of the vinyloxy radical by ns time-resolved laser flash photolysis
The photochemistry of two Barton esters, one derived from a dioxolane carboxylic acid and the other from pivalic acid, was investigated by product analysis and nanosecond laser flash photolysis (LFP). As expected, photolysis of the pivalate ester resulted in formation of the pyridine-2-thiyl and the t-butyl radical. Photolysis of the Barton ester of 2,2-dimethyl-1,3-dioxolane-4-carboxylic acid, on the other hand, revealed a complex multi-step fragmentation. In addition to the pyridine-2-thiyl and dioxolanyl radical, we gained evidence for the formation of the vinyloxy radical, CH2[double bond, length as m-dash]CHOË. The latter was identified in the LFP by its Ï-complexes with benzene and diphenylether, its rapid quenching by electron-rich arenes and tri-n-butyl tin hydride, and its oxidative power in presence of trifluoroacetic acid as demonstrated by the oxidation of ferrocene to ferrocenium. Formation of CH2[double bond, length as m-dash]CHOË can be rationalized via fragmentation of the dioxolanyl radical. As the calculated barriers are too high for the reaction sequence to occur on the LFP time scale, we investigated the fragmentation of the photoexcited Barton ester via BornâOppenheimer molecular dynamics simulations. In one trajectory, we could observe all reaction steps including ring opening of the dioxolanyl radical, suggesting that the excess energy gained in the ester cleavage and decarboxylation may lead to fragmentation of the hot dioxolanyl radical
The elusive aldol reaction of enolates with aldolates - a highly stereoselective process using three different carbonyl components
Remarkable Oxidation Stability of Glycals: Excellent Substrates for Cerium(IV)-Mediated Radical Reactions
Adsorption structure determination of a large polyaromatic trithiolate on Cu(111): Combination of LEED-I(V) and DFT-vdW
The adsorption geometry of 1,3,5-tris(4-mercaptophenyl)benzene (TMB) on Cu(111) is determined with high precision using two independent methods, experimentally by quantitative low energy electron diffraction (LEED-I(V)) and theoretically by dispersion corrected density functional theory (DFT-vdW). Structural refinement using both methods consistently results in similar adsorption sites and geometries. Thereby a level of confidence is reached that allows deduction of subtle structural details such as molecular deformations or relaxations of copper substrate atoms
Impact of the level of complexity in self-sorting: Fabrication of a supramolecular scalene triangle
The impact of the level of complexity in self-sorting was elaborated through the fabrication of various scalene triangles. It turned out that the self-sorting system with a higher level of complexity was far superior to less complex sorting algorithms
Dual coordination in ditopic azabipyridines and azaterpyridines as a key for reversible switching
Enol Radical Cations in Solution. 13. First Example of a Radical Dication Rearrangement. One-Electron Oxidation of Dihydrobenzofuranyl Cations Leads to Drastic Rate Enhancement in the Oxidative Benzofuran Formation from Enols
Remote control of the synthesis of a [2]rotaxane and its shuttling via metalâion translocation
Remote control in an eightâcomponent network commanded both the synthesis and shuttling of a [2]rotaxane via metalâion translocation, the latter being easily monitored by distinct colorimetric and fluorimetric signals. Addition of zinc(II) ions to the red colored copperâion relay station rapidly liberated copper(I) ions and afforded the corresponding zinc complex that was visualized by a bright sky blue fluorescence at 460â
nm. In a mixture of all eight components of the network, the liberated copper(I) ions were translocated to a macrocycle that catalyzed formation of a rotaxane by a doubleâclick reaction of acetylenic and diazide compounds. The shuttling frequency in the copperâloaded [2]rotaxane was determined to k298=30â
kHz (ÎHâ =62.3±0.6â
kJâmolâ1, ÎSâ =50.1±5.1â
Jâmolâ1âKâ1, ÎGâ 298=47.4â
kJâmolâ1). Removal of zinc(II) ions from the mixture reversed the system back generating the metalâfree rotaxane. Further alternate addition and removal of Zn2+ reversibly controlled the shuttling mode of the rotaxane in this eightâcomponent network where the ion translocation status was monitored by the naked eye
Five-State Rotary Nanoswitch
In our quest to develop artificial
multistate devices, we synthesized
the nanomechanical switch <b>1</b> that is characterized by
a tetrahedral core equipped with four pending arms. The rotary arm
with its azaterpyridine terminal is intramolecularly coordinated to
a zincÂ(II) porphyrin station that is the terminus of another arm in <b>1</b>. The two other arms carry identical sterically shielded
phenanthroline stations. The 2-fold alternate addition of a copperÂ(I)
ion and [1,10]-phenanthroline (1 equiv each) results in the formation
of five different switching states (State Iâ State IIâ
State IIIâ State IVâ State V â State I), which
force the toggling arm to move back and forth between the zincÂ(II)
porphyrin and phenanthroline stations separated by a distance of 25
Ă
. All switching states constitute clean single species, except
for State III, and thus are fully characterized by spectroscopic methods
and elemental analysis. Finally, the initial state of nanoswitch was
reset by addition of cyclam for complete removal of the copperÂ(I)
ions
- âŠ