- Isoselective Lactide Ring Opening Polymerisation using [2]Rotaxane Catalysts
-
Polylactide (PLA) is a fully biodegradable and recyclable plastic, produced from a bio-derived monomer: it is a circular economy plastic. Its properties depend upon its stereochemistry and isotactic PLA shows superior thermal-mechanical performances. Here, a new means to control tacticity by exploiting rotaxane conformational dynamism is described. Dynamic achiral [2]rotaxanes can show high isoselectivity (Pi=0.8, 298 K) without requiring any chiral additives and enchain by a chain end control mechanism. The organocatalytic dynamic stereoselectivity is likely applicable to other small-molecule and polymerization catalyses.
- Lim, Jason Y. C.,Yuntawattana, Nattawut,Beer, Paul D.,Williams, Charlotte K.
-
supporting information
p. 6007 - 6011
(2019/04/03)
-
- Formation of a highly-ordered rigid multichromophoric 3D supramolecular network by combining ionic and coordination-driven self-assembly
-
We present here the self-assembly of a green-emitting metallosupramolecular rhomboid into a rigid, highly-ordered 3D multichromophoric network through the mediation of a tetra-anionic violet-blue molecular emitter. Control was obtained on the spatial topology, the electronic energy landscape and the fluorescence polarization of the interacting dipoles.
- Kaloudi-Chantzea, Antonia,Martinou, Elisabeth,Seintis, Kostas,Karakostas, Nikolaos,Giastas, Petros,Pitterl, Florian,Oberacher, Herbert,Fakis, Mihalis,Pistolis, George
-
supporting information
p. 3388 - 3391
(2016/02/27)
-
- VARIABLE TEMPERATURE ESR SPECTRA OF 1-(3,4,5-TRIMETHOXY-BENZOYL)-2,2-BIS(3,5-DI-TERT-BUTYL-PHENYL)HYDRAZYL AND ITS 1-(15)N-CONGENER
-
The title free radicals were obtained by oxidation of the corresponding hydrazines which were synthesized and characterized by elemental analysis, IR and 1H-NMR spectra. The ESR spectra of the free radicals were recorded in toluene in the temperature range -50 deg C to +90 deg C. The simulated ESR spectra indicate a higher spin density at the tricoordinated N-2 nitrogen of the diarylamino group (hfc aN = 0.862 mT) than at the dicoordinated N-1 nitrogen atom (hfc aN = 0.830 mT). In the temperature range 0 deg C to 30 deg C the activation free energy for interconversion of conformers was determined to be ΔG(excit.) = 7.80 kcal/mol.
- Crasovschi, Afanase,Grecu, Nicoleta,Negoita, Nicolae,Caproiu, Miron Teodor,Balaban, Alexandru T.
-
p. 1335 - 1340
(2007/10/03)
-
- 3,5-Di-tert-butylthiobenzoyltriphenylsilane: a versatile spin trapping agent
-
3,5-Di-tert-butylthiobenzoyltriphenylsilane (DBTBTPS) has been synthesized and tested as a spin trapping agent for electron spin resonance studies.Upon reaction with a variety of radicals of different nature inside the cavity of the ESR spectrometer.DBTBTPS leads to the observation of rather persistent spectra which in nearly all cases allow the unambiguous identification of the trapped species, DBTBTPS is somewhat less stable than thiobenzoyltriphenylsilane (TBTPS), the unsubstituted thiobenzoyltriphenylsilane; yet, as it affords spin adducts whose spectra are characterized by a smaller number of lines, it may prove more useful than TBTPS itself when dealing with radicals leading to species with a large number of magnetically active nuclei interacting with the unpaired electron.
- Alberti, Angelo,Benaglia, Massimo
-
p. 151 - 158
(2007/10/02)
-
- FURTHER STUDIES ON THE EXTENDED HAMMETT EQUATION COMPRISING THE HYDROPHOBIC CONSTANT: REACTIVITY DATA FOR BENZOIC ACIDS, ARYLACETIC ACIDS, β-ARYLPROPIONIC ACIDS, trans- AND cis-CINNAMIC ACIDS, METHYL BENZOATES; DISSOCIATION CONSTANTS, DDM REACTION AND ALKALINE HYDROLYSIS IN VARIOUS W...
-
The extended Hammett equation Δ = ρ? + h? comprising the hydrophobic constant ? is found to be effective in the title compounds and reactivities in various solvent mixtures.In 32 vol.percent tert-butanol-water hm decreases in the order ArCOOMe (-0.25), cis-ArCH=CHCOOH (-0.18), ArCOOH and ArCH2COOH (-0.16), ArCH2CH2COOH and trans-ArCH=CHCOOH (-0.07).For ArCOOH, mixtures like 40-60percent methanol, 50percent ethanol, 50percent acetone and 50percent dioxane give similar hm values of circa -0.05.For ArCH2COOH the effects of 3-iodo and 4-iodo substituents are acid-weakening in32percent tert-butanol.The consequences of the h? term for ρ, ?, and the averaging of ? values, are discussed.
- Hoefnagel, Anthonius J.,Wepster, Bartholomeus M.
-
p. 119 - 135
(2007/10/02)
-
- SELECTIVE MONO- OR DIMETALATION OF ARENES BY MEANS OF SUPERBASIC REAGENTS
-
If employed in tetrahydrofuran, stoichiometric amounts of butyllithium and potassium tert-butoxide react with benzene under clean monometalation.In hexane suspension, however, considerable amounts of meta- and para-disubstituted by-products are obtained (approx. 10percent).They become preponderant if a three-fold excess of the metalating agent is used.Naphthalene leads under the same conditions to a mixture of two mono- and ten di-substituted derivatives. - Alkyl groups, as present in tert-butylbenzene, retard the metalation at both m- and p-positions, while trialkylsilyl groups deactivate only m-position.In either case exclusive monosubstitution occurs. - Perdeuterobenzene undergoes metalation and subsequent electrophilic mono- or disubstitution to afford isotope labeled compounds with moderate, though synthetically attractive yields.The kinetic isotope effects and product ratios can be taken as evidence for aggregate formation at the level of both the superbasic metalating reagent and the organometallic intermediates.
- Schlosser, Manfred,Choi, Jung Hoon,Takagishi, Sadahito
-
p. 5633 - 5648
(2007/10/02)
-
- Factors Affecting the Stability and Equilibria of Free Radicals. 14. Unexpected Spin Densities in 1-(Trifluoroacetyl)-2,2-diarylhydrazyl Revealed by 15N Labeling
-
1-(Trifluoroacetyl)-2,2-bis(3,5-di-tert-butylphenyl)hydrazyl and its congener labeled at the dicoordinated 1-nitrogen atom with 15N were prepared.ESR spectra of solutions of both compounds were recorded and hyperfine coupling constants determined by optimizing simulated spectra.Unlike all other 1,2,2-triarylhydrazyls which have been investigated, the hyperfine coupling constant for the dicoordinated nitrogen is lower (0.7 mT) than that for the tricoordinated nitrogen (1.0 mT) in this free radical.This striking result raises questions about the mode of trifluoroacetyl group participation in ? electron delocalization.
- Bologa, Ursula,Balaban, Alexandru T.,Grecu, Nicoleta,Negoita, Nicolae,Caproiu, Miron T.,Walter, Robert I.
-
p. 4176 - 4179
(2007/10/02)
-
- The 1-(3,5-Di-tert-butylphenyl)-1-methylethoxycarbonyl (t-Bumeoc) Residue, a Protecting Group Cleavable under Extremely Mild Acidic Conditions
-
The synthesis of 1-(3,5-di-tert-butylphenyl)-1-methylethoxycarbonyl fluoride (8) and its reaction with selected amino acids as well as the 13C NMR spectroscopic characterization of t-Bumeoc derivatives are described.The new protecting group is cleavable under very mild acidic conditions.The kinetics of the cleavage is studied by high-performance liquid chromatography (HPLC).The utility of the t-Bumeoc compared to the Adpoc protecting group is demonstrated taking a derivative of the molluscan neuropeptide as an example.
- Voelter, Wolfgang,Mueller, Juergen
-
p. 248 - 260
(2007/10/02)
-