Reductive decoupling

Reductive decoupling, 181, 187 Reductive elimination, 171-174, 190-197 refined catalytic cycle, 206-211 and selectivity, 212-214 steric and electronic factors, 202-205, 217 Retro-Wittig decomposition, 37, 78, 79-83 thiobetaines, 57-58, 60, 65 Ring cleavage, 105, 276, 281 Ring closure in oligomerization, 172, 174, 190-197... 

Matrix 4. Evaluation matrix for the reductive decoupling of a five-membered metallacycle. For explanation, see Matrix 1. 

Oxidative-Coupling and Reductive-Decoupling. Examples of oxidative-coupling and reductive-decoupling of ligands about a dimetal center are seen in the work of Stone, Knox and their coworkers (40) and are not discussed here. 

Decomposition of metallacyclopentane compounds may occur either via reductive cycloelimination (reductive decoupling) (Table 1.4) with ethylene evolution or because of reductive elimination leading to the formation of cyclobutane. 

Oxidative coupling consists in coupling two ligands by formation of a covalent bond between them. This reaction goes along with the increase of two nnits of the metal oxidation state (which justifies its name) and the decrease of its NVE and NNBE by two units. The coordinance remains unchanged. The opposite reaction, reductive decoupling, is rarely encountered. 

The first finite element schemes for differential viscoelastic models that yielded numerically stable results for non-zero Weissenberg numbers appeared less than two decades ago. These schemes were later improved and shown that for some benchmark viscoelastic problems, such as flow through a two-dimensional section with an abrupt contraction (usually a width reduction of four to one), they can generate simulations that were qualitatively comparable with the experimental evidence. A notable example was the coupled scheme developed by Marchal and Crochet (1987) for the solution of Maxwell and Oldroyd constitutive equations. To achieve stability they used element subdivision for the stress approximations and applied inconsistent streamline upwinding to the stress terms in the discretized equations. In another attempt, Luo and Tanner (1989) developed a typical decoupled scheme that started with the solution of the constitutive equation for a fixed-flow field (e.g. obtained by initially assuming non-elastic fluid behaviour). The extra stress found at this step was subsequently inserted into the equation of motion as a pseudo-body force and the flow field was updated. These authors also used inconsistent streamline upwinding to maintain the stability of the scheme. 

The optical absorption spectra and the first reduction potentials are virtually independent of the number of pyrene units present in the molecule, as a result of the specific stereoelectronic situation. Since the orbital coefficients of the bridgehead centers are almost zero, the rings are electronically decoupled. Thus, oligopyrenes differ significantly from oligo(pflrfl-phenylene)s (OPVs). 

Fig. 3 shows a portion of the aliphatic region of the proton-decoupled, C-n.m.r. spectra of virgin glycophorin and fully reductively [ C]methy-... 

Fig. 3.—A Portion of the Aliphatic Region of the Proton-decoupled, C-N.m.r. Spectra of Native Glycophorin A (in HjO at 30°) and Fully Reductively [ C]Methylated Glycophorins A, A , and A (in H2O at 30°), at 22.5 MHz. [Taken from Ref. 56. Time-domain data were accumulated in 8192 addresses, with a recycle time of 1 s (except for A, where 2 s was used). A digital broadening of 2.8 Hz was applied (A) 1.9 mM virgin glycophorin A, at pH 6.5, after 50,000 accumulations (B) 1.6 mM fully reductively [ C]methylated glycophorin A , at pH 8.5, after 12,015 accumulations (C) 1.6 mM fully reductively [ C]methylated glycophorin A, at pH 7.3, after 14,208 accumulations (D) 1.5 mM fully reductively [ C]methylated glycophorin A °, at pH 7.2, after 12,815 accumulations.]...

Fig. 5.—Proton-decoupled, C-N.m.r. Spectra (at 22.5 MHz) of the Partial-reductive, [ C]Methylation Studies of —1.5 mM Glycophorin in H2O at 30°. [Spectra of methylated...

Fig. 12 shows a portion of the aliphatic region (30-50 p.p.m.) of the proton-decoupled, C-n.m.r. spectra of fully reductively [ C]methylated glycophorin A" " and glycophorin B. Glycophorin B was isolated from heterozygous, red-blood cells, and was then separated from glycophorin A by gel-filtration chromatography on Ammonyx-Lo. Clearly, the... 

Crowe et al. (1983) proposed an elegant strategy for decoupling measured variables from the linear constraint equations. This procedure allows both the reduction of the data reconciliation problem and the classification of process variables. It is based on the use of a projection matrix to eliminate unmeasured variables. Crowe later extended this methodology (Crowe, 1986, 1989) to bilinear systems. 

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