Erythro definition

Of course, the trans isomer will give the opposite results the threo pair if the addition is syn and the erythro pair if it is anti. The threo and erythro isomers have different physical properties. In the special case where Y=W (as in the addition of Br2), the erythro pair is a meso compound. In addition to triple-bond compounds of the type ACsCA, syn addition results in a cis alkene and anti addition in a trans alkene. By the definition given on page 166 addition to triple bonds cannot be stereospecific, though it can be, and often is, stereoselective. 

Analysis of the distribution of 4a-7a shows a definite preference for erythro arrangements in addition to the stereocontrol provided by the auxiliary compare n = 1 selectivity (Table 3) with selectivity in n = 2 telomers (Fig. 4). The temperature dependence of selectivity was studied and A(A//) and A(A5) were obtained. As expected, selectivity was greater at lower temperatures. Eyring plots for the three selectivities (addition of the second monomer to the n = 1 radical, allyl transfer... 

Stereoselectivity. See Asymmetric induction Axial/equatorial-, Cis/trans-, Enantio-, Endo/exo- or Erythro/threo-Selectivity Inversion Retention definition (e.e.), 107 footnote Steric hindrance, overcoming of in acylations, 145 in aldol type reactions, 55-56 in corrin synthesis, 261-262 in Diels-Alder cyclizations, 86 in Michael type additions, 90 in oiefinations Barton olefination, 34-35 McMurry olefination, 41 Peterson olefination, 33 in syntheses of ce-hydrdoxy ketones, 52 Steric strain, due to bridges (Bredt s rule) effect on enolization, 276, 277, 296, 299 effect on f3-lactam stability, 311-315 —, due to crowding, release of in chlorophyll synthesis, 258-259 in metc-cyclophane rearrangement, 38, 338 in dodecahedrane synthesis, 336-337 in prismane synthesis, 330 in tetrahedrane synthesis, 330 —, due to small angles, release of, 79-80, 330-333, 337... 

Unfortunately, there is more than one definition for threo- and erythro. Winstein and co-workers gave the following definition of these diastereomers In a compound with two asymmetric carbons that has two common ligands and a third that differs, the isomers that would be meso if the third ligand were identical are erythro diastereomers.An alternative definition is If two asymmetric carbons have only one ligand in common, then the other four ligands are paired in the same commonsense way and isomers that would have equal pairs eclipsed in any conformation are erythro. Eliel, Mislow and their co-workers defined erythro and threo in terms of Fischer projections. The aldol products (see sec. 9.4.A) 68 and 69, and the ester-aldehyde condensation products 70 and 71.30 shown with the erythro and threo notation. 

D-Erythro-ascorbic acid D-Erythro-hex-2-enonic acid, y-lactone D-Erythro-3-ketohexonic acid lactone Glucosaccharonic acid Isoascorbic acid D-lsoascorbic acid Isovitamin C Saccharosonic acid Definition Isomer of ascorbic acid Empirical CeHsOe... 

Several possibilities exist for ditacticity in macromolecules formed by polymerizing 1,2-disubstituted ethylenes of the type RHC=CHR, structures (XVIII)-(XX). It can be seen that each unit contains two different asymmetric carbon atoms in the chain. The original definitions of tacticity have been extended to include these modifications and Newman s (1956) definitions of erythro and threo structures. Structures (XVIII)-(XX) illustrate ifereo-diisotactic, erythro-diisotactic, and disyndiotactic poisoners, respectively. 

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