A mixture of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) radical and 2,2,6,6-tetramethyl-1-piperidine (TEMP) was included into organic 1-D nanochannels of tris(o-phenylenedioxy)cyclotriphosphazene (TPP) crystal. Dilution of the paramagnetic TEMPO radical was achieved with excess TEMP, thereby isolating a TEMPO molecule in the nanochannel. For inclusion compounds of TPP with TEMPO and TEMP (TEMPO/all guest compounds = 0.017, and 0.15), temperature-dependent electron spin resonance (ESR) spectra were observed to investigate their molecular dynamics and orientation. In the temperature range from 112 K to room temperature, the spectra depended remarkably on the temperature. Temperature dependence was well interpreted by uniaxial rotation, suggesting that TEMPO molecules undergo uniaxial rotation about a channel axis with a molecular orientation in which the N-O bond in the nitroxide group is perpendicular to the channel axis. The activation energy of uniaxial rotation was evaluated as 4.5 +/- 0.3 kJ mol(-1). 相似文献
Summary: The formation of a molecular‐complex crystalline phase of syndiotactic polystyrene (sPS) that contains a stable nitroxide radical compound, 2,2,6,6‐tetramethylpiperidinyl‐N‐oxyl (TEMPO), is confirmed by IR and electron spin resonance (ESR) spectroscopy, X‐ray diffractometry, and thermogravimetric analysis. Through a guest exchange procedure assisted by a plasticizing agent, the original guest (chloroform) contained in the starting clathrate phase is completely replaced by TEMPO. Although the conformational regularity of the sPS helices in the resultant crystalline phase that contains TEMPO is similar to that in the starting clathrate phase, the host lattice expands in the 010 direction. The guest TEMPO molecules exhibit a significantly broadened ESR signal because of their highly concentrated state in the complex crystalline phase.
Thermogravimetric measurement of a powder sample of the sPS/TEMPO complex. 相似文献
[Fe(tvp)2(NCS)2] ( 1 ) (tvp=trans‐(4,4′‐vinylenedipyridine)) consists of two independent perpendicular stacks of mutually interpenetrated two‐dimensional grids. This uncommon supramolecular conformation defines square‐sectional nanochannels (diagonal≈2.2 nm) in which inclusion molecules are located. The guest‐loaded framework 1@guest displays complete thermal spin‐crossover (SCO) behavior with the characteristic temperature T1/2 dependent on the guest molecule, whereas the guest‐free species 1 is paramagnetic whatever the temperature. For the benzene–guest derivatives, the characteristic SCO temperature T1/2 decreases as the Hammet σp parameter increases. In general, the 1@guest series shows large entropy variations associated with the SCO and conformational changes of the interpenetrated grids that leads to a crystallographic‐phase transition when the guest is benzonitrile or acetonitrile/H2O. 相似文献
Summary: 2,2,6,6‐Tetramethylpiperidine 1‐oxyl (TEMPO)‐containing N‐propargylamide HCCCH2NHCO‐4‐TEMPO ( 1 ), propargyl ester HCCCH2OCO‐4‐TEMPO ( 2 ), phenylacetylene derivative HCCC6H3‐3,4‐(CO2‐4‐TEMPO)2 ( 3 ), and norbornene diester monomers, NB‐2,3‐exo,exo‐(CH2OCO‐4‐TEMPO)2 ( 4 ), NB‐2,3‐endo,exo‐(COO‐4‐TEMPO)2 ( 5a ), NB‐2,3‐endo,endo‐(COO‐4‐TEMPO)2 ( 5b ) (NB = norbornene, TEMPO = 2,2,6,6‐tetramethyl‐1‐piperidinyloxyl) were synthesized and polymerized with rhodium and ruthenium catalysts. Monomers 2 , 5a , and 5b gave polymers with number‐average molecular weights of 47 000–185 000 in 59–100% yields, while 1 , 3 , and 4 gave polymers insoluble in common organic solvents in 88–100% yields. The capacities of cells fabricated with poly( 1 ), poly( 2 ), and poly( 3 ) were 67, 82, and 23 Ah · kg−1 based on the weight, respectively. The capacity of poly( 5a )‐based cell reached the theoretical value (109 Ah · kg−1) of the polymer.
Charge–discharge curves of poly( 5a ) at a current density of 0.13 mA · cm−2 (100 mA · g−1‐cathode active material) in the voltage range of 2.5–4.2 V. 相似文献
Synergism among several intertwined catalytic cycles allows for selective, room temperature oxidation of primary amines to the corresponding nitriles in 85–98 % isolated yield. This metal‐free, scalable, operationally simple method employs a catalytic quantity of 4‐acetamido‐TEMPO (ACT; TEMPO=2,2,6,6‐tetramethylpiperidine N‐oxide) radical and the inexpensive, environmentally benign triple salt oxone as the terminal oxidant under mild conditions. Simple filtration of the reaction mixture through silica gel affords pure nitrile products. 相似文献
Living free‐radical butyl acrylate polymerization in miniemulsion was initiated by polystyrene bearing a nitroxyl end group to yield polystyrene‐block‐poly(butyl acrylate) block copolymers. Polystyrene macroinitiator was obtained using different initiating systems (potassium persulfate or benzoyl peroxide) in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) or the more water‐soluble 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐N‐oxyl (OH‐TEMPO). The nitroxide water‐solubility has an important influence in determining molecular weight distribution and controlling the growth of the second block. 相似文献
Introduction Nitroxides such as 2,2,6,6-tetramethylpiperidine-N- oxyl (TEMPO) are well-known stable free radicals which have been extensively used in spin labeling,1 spin trapping2 and as antioxidants.3 Nitroxides are also easy to undergo reversible one-electron oxidation to form the corresponding oxoammonium ions.4 Oxoammonium ions are mild one-electron oxidants which have been used in organic synthesis5-8 and to generate radical cations.9 We10 found recently that electrochemically generat… 相似文献
Potenital pathways for the deactivation of hindered amine light stabilisers (HALS) have been investigated by observing reactions of model compounds--based on 4-substituted derivatives of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO)--with hydroxyl radicals. In these reactions, dilute aqueous suspensions of photocatalytic nanoparticulate titanium dioxide were irradiated with UV light in the presence of water-soluble TEMPO derivatives. Electron spin resonance (ESR) and electrospray ionisation mass-spectrometry (ESI-MS) data were acquired to provide complementary structural elucidation of the odd- and even-electron products of these reactions and both techniques show evidence for the formation of 4-oxo-TEMPO (TEMPONE). TEMPONE formation from the 4-substituted TEMPO compounds is proposed to be initiated by hydrogen abstraction at the 4-position by hydroxyl radical. High-level ab initio calculations reveal a thermodynamic preference for abstraction of this hydrogen but computed activation barriers indicate that, although viable, it is less favoured than hydrogen abstraction from elsewhere on the TEMPO scaffold. If a radical is formed at the 4-position however, calculations elucidate two reaction pathways leading to TEMPONE following combination with either a second hydroxyl radical or dioxygen. An alternate mechanism for conversion of TEMPOL to TEMPONE via an alkoxyl radical intermediate is also considered and found to be competitive with the other pathways. ESI-MS analysis also shows an increased abundance of analogous 4-substituted piperidines during the course of irradiation, suggesting competitive modification at the 1-position to produce a secondary amine. This modification is confirmed by characteristic fragmentation patterns of the ionised piperidines obtained by tandem mass spectrometry. The conclusions describe how reaction at the 4-position could be responsible for the gradual depletion of HALS in pigmented surface coatings and secondly, that modification at nitrogen to form the corresponding secondary amine species may play a greater role in the stabilisation mechanisms of HALS than previously considered. 相似文献
An effective transition‐metal‐free catalytic system is developed for aerobic oxidations of alcohols. Using catalytic amount of bromide‐bromate coupling, H2SO4, and NaNO2, together with 2,2,6,6‐tetramethylpiperidine N‐oxyl radical (TEMPO) in the presence of air, various alcohols could be converted into the corresponding aldehydes or ketones in good to excellent isolated yields under mild conditions. 相似文献
An electrochemical approach to the intramolecular aminooxygenation of unactivated alkenes has been developed. This process is based on the addition of nitrogen‐centered radicals, generated through electrochemical oxidation, to alkenes followed by trapping of the cyclized radical intermediate with 2,2,6,6‐tetramethylpiperidine‐N‐oxyl radical (TEMPO). Difunctionalization of a variety of alkenes with easily available carbamates/amides and TEMPO affords aminooxygenation products in high yields and with excellent trans selectivity for cyclic systems (d.r. up to>20:1). The approach provides a much‐needed complementary route to existing cis‐selective methods. 相似文献