Configurational isomerization

Butadiene could be polymerized using free radical initiators or ionic or coordination catalysts. When butadiene is polymerized in emulsion using a free radical initiator such as cumene hydroperoxide, a random polymer is obtained with three isomeric configurations, the 1,4-addition configuration dominating ... 

Novolac resins, as the oldest synthetic polymers, have played an important role 1n microelectronic Industry as positive photoresists. Studies of novolac dissolution have populated the literature a recent survey shows that the rate of dissolution 1s influenced by the concentration of the alkali, size of the cation, addition of salt, and the presence of dissolution Inhibitors (1-6). The voluminous experimental results, however, have not led to a clear understanding of the dissolution phenomena. Arcus (3) proposed an 1on-permeab1e membrane" model while Szmanda (1) and Hanabata (6) emphasized the Importance of secondary structures of novolac molecules, for Instance, Inter- or Intramolecular hydrogen bonding and the various isomeric configurations of the resins. These important contributions nevertheless point to a need for additional studies of the mechanism of dissolution. 

First, most naturally occurring unsaturated fatty acids have double bonds in the cis isomeric configuration. .. 

Fig. 7. This diagram resembles Fig. 5. However, the energy surface is lowered for the isomeric configurations a and b as well as for the activated molecule in the presence of the catalyst. Hence the normal molecules will be more strongly adsorbed than in the case shown in Fig. 5. The activation energy is lowered by a larger amount than the energy of the normal molecules, so that the surface still has a conventional catalytic action.

Biesalski, FI. K. (1990). Quantitative and qualitative microdetermination of different fatty acid esters of retinol including their isomeric configurations in small tissue samples. Methods Enzymol. 189, 83-91. 

The aim of the present study is to investigate the validity of the pairwise additivity of two-body and three-body potentials for He2Br2. These results are compared with ah initio calculations" and a simple model of the three-body potential is proposed to determine well depths and equilibrium structures for different isomeric configurations of the complex, as well as the minimum energy pathways through them. Additionally, variational methods are used to calculate the vibrational states of He2Br2. The wavefunctions of the lower states are analyzed in terms of probability distributions of the internal coordinates and the zero-point energy of the vdW cluster is evaluated. 

ATP -I- 5-diphospho-lD-myo-inositol-pentakisphosphate = ADP -h bis(di-phospho)- D-myo-inositol tetrakisphosphate (isomeric configuration unknown)... 

Stereoisomers among the tetpenes are abundant and exceedingly important to the chemistry of the field. Stereochemical nomenclature therefore cannot be ignored in any complete scheme for systematizing terpene nomenclature for the present, however, the recommendations in this report provide only structural names for the simple acyclic, monocyclic, and bicyclic terpene hydrocarbons. Studies in various fields — e.g., steroids — on preferred methods of designating isomeric configurations are being made by other committees (1, 21, 25). 

The chemistry of the pungent compounds of pepper has been under study since the isolation of piperine in 1820. Piperine was shown to be a piperidide of piperic acid, and had the trans. trans configuration. The three other possible isomers were soon postulated, and they were named isopiperine (cis.trans). isochavicine (trans. cis) and chavicine (cis.cis) even before they were synthesized. The assignment of the isomeric configuration starts from the amide end. 

Just like triazenes (Sections II,B,2-II,B,4), tetrazenes can isomerize with change of conformation (rotational isomerization), configuration (cis-trans isomerization), and constitution (1,3- and 1,4-rearrangements). 

The dimethyl amine derivative produced was quaternized directly by methyl iodide, added slowly to a chilled solution of the ternary amine in ethyl acetate. When other ring substituents are present, the reductive eunination leads to isomeric configurations, as noted in Table I. Quaternary ammonium halide salts were characterized by melting point, TLC, or microanalytical data and and NMR. 

In free retinal, illumination will produce a mixture of several single- and doublebond isomeric configurations. Protein-bound retinal is more restricted in its motional possibilities in the rhodopsins the binding pocket is tailored to fit only a few specific retinal configurations. Indeed, the light-initiated reaction cycles of the bacterial rhodopsins are based exclusively on dlX-trans to 13-cw isomerization of their retinal chromophores. When under some conditions other isomers are produced upon illumination, such as 9 cis, they accumulate in limited quantities [90-92]. 

T ris( A -carbamoy 1 methy 1 jcyclam has been prepared by reacting cyclam with iodoacetamide in acetone plus di-isopropylethylamine.120 l,8-Bis[AA(A,A-dimethylcarbamoylmethyl)]-4,l 1-dimethylcyclam forms isomeric configuration I and III compounds, [Cu(L)](BF4)2, for which interconversion is promoted by electrochemical reduction.121... 

These hydroximidates and thiolhydroximidates may exist in E and Z forms. Both isomers were isolated only with the unsubstituted [2.2.1] thia system, although the presence of both isomers in other reaction mixtures cannot be excluded. Compounds 1 and 39 were shown to be the Z-isomer by single crystal x-ray crystallography. The Z-form has been shown to be the stable isomer of methomyl (116). The more stable isomer of methyl acetohydroximidate and related compounds possesses the E-configuration 07). We have no information on the isomeric configuration of the present bicyclic hydroximidates other than that they appear to be single isomers. 

The simplest unit is 1,4-isoprene, although there are two distinct cis and trans isomeric configurations of 1,4-polyisoprene. 

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