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Abstract DMSO, an interesting solvent for copper‐catalyzed living radical polymerization (LRP) mediated by disproportionation, does not exhibit the greatest disproportionation of Cu(I)X into Cu(0) and Cu(II)X2. Under suitable conditions, DMSO provides 100% conversion and absence of termination, facilitating the development of complex‐architecture methodologies by living and immortal polymerizations. The mechanism yielding this level of precision is being investigated. Here we compare Cu(0)‐wire‐catalyzed LRP of methyl acrylate mediated by disproportionating ligands tris(2‐dimethylaminoethyl)amine, Me6‐TREN, tris(2‐aminoethyl)amine, TREN, and Me6‐TREN/TREN = 1/1 in presence of eight disproportionating solvents, some more efficient than DMSO in disproportionation. Unexpectedly, we observed that all solvents increased the rate of polymerization when monomer concentration decreased. This reversed trend from that of conventional LRPs demonstrates catalytic effect for disproportionating solvents. Above a certain concentration, the classic concentration‐rate dependence was observed. The external order of reaction of the apparent rate constant of propagation,kpappon solvent concentration demonstrated the highest order of reaction for the least disproportionating DMSO. Of all solvents investigated, DMSO has the highest ability to stabilize Cu(0) nanoparticles and therefore, yields the highest activity of Cu(0) nanoparticles rather than their greatest concentration. The implications of the catalytic effect of solvent in this and other reactions were discussed.
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Effect of the solvent on the conformation of monocrotaline as determined by isotropic and anisotropic NMR parameters
Abstract The conformation in solution of monocrotaline, a pyrrolizidine alkaloid presenting an eleven‐membered macrocyclic diester ring, has been investigated using a combination of isotropic and anisotropic nuclear magnetic resonance parameters measured in four solvents of different polarity (D2O, DMSO‐d6, CDCl3, and C6D6). Anisotropic nuclear magnetic resonance parameters were measured in different alignment media, based on their compatibility with the solvent of interest: cromoglycate liquid crystal solution was used for D2O, whereas a poly (methyl methacrylate) polymer gel was chosen for CDCl3and C6D6, and a poly (hydroxyethyl methacrylate) gel for DMSO‐d6. Whereas the pyrrolizidine ring shows anE6exo‐puckered conformation in all of the solvents, the macrocyclic eleven‐membered ring adopts different populations ofsyn‐parallel andanti‐parallel relative orientation of the carbonyl groups according to the polarity of the solvent.
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- Award ID(s):
- 1726525
- PAR ID:
- 10451985
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Magnetic Resonance in Chemistry
- Volume:
- 59
- Issue:
- 5
- ISSN:
- 0749-1581
- Format(s):
- Medium: X Size: p. 561-568
- Size(s):
- p. 561-568
- Sponsoring Org:
- National Science Foundation
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