Geometric isomerism configurations

Oxazol-5(2H)-one, 2-benzylidene-4-methyl-tautomerism, 6, 186 Oxazol-5(2ff)-one, 2-methylene-isomerization, 6, 226 Oxazol-5(2H)-one, 2-trifluoromethyl-acylation, 6, 201 Oxazol-5(4ff)-one, 4-allyl-thermal rearrangements, 6, 199 Oxazol-5(4H)-one, 4(arylmethylene)-Friedel-Crafts reactions, 6, 205 geometrical isomerism, 6, 185 Oxazol-5(4ff)-one, 4-benzylidene-2-phenyl-configuration, 6, 185 photorearrangement, 6, 201 Oxazol-5(4ff)-one, 4-benzyl-2-methyl-Friedel-Crafts reactions, 6, 205 Oxazol-5(4ff)-one, 4-methylene-in amino acid synthesis, 6, 203 Oxazol-5(4ff) -one. 2-trifluoromethyl-hydrolysis, 6, 206 Oxazolones... 

Geometric Isomerism involves double bond C = C atoms. Geometric Isomerism arises from different configurations of the substituents on a carbon double bond and depends on the positions occupied by the substituent groups in space. For example, considering 1, 3-butadiene polymerisation. 

Owing to the relative rigidity of the carbon-nitrogen double bond, oximes can exist in two discrete geometrically isomeric forms the E or anti isomer anti-E-217) and the (Z) or syn isomer (syn-Z-217) (equation 70). In solid state, both oximes show high configurational stability and discrete existence. In solution, equilibrium between both isomers is rapidly established, favouring the thermodynamically most stable isomer " ... 

Consider the two configurations of 2-butene in Figure 1-9 and remember that the carbon-carbon double bond does not permit the rotation of the carbon atoms. Notice that in one case the two methyl groups are located on the same side of the basic structure while in the other case the methyl groups are located on opposite sides of the structure. These two molecules exhibit geometric isomerization because of the way the atoms are oriented in space, even though they are alike... 

The introduction of more than one C- or jV-substituted en ring into the coordination sphere considerably increases the isomeric complexity. Many of these ligands are now unsymmetrical and their complexes may exhibit geometric isomerism dependent upon the end-for-end orientation.257 Thus there are 24 distinct configurational and conformational forms expected for Co(R,5-pn)3+, 258 Table 6 lists a variety of C- and JV-substituted ethylenediamine type ligands that have been investigated. 

The tocotrienols possess one centre of asymmetry, at C-2, in addition to the sites of geometrical isomerism at C-3 and C-7. The equivalent natural tocotrienols to the tocopherols mentioned above have a (IKyi -trans-T-trans configuration [44-47]. Indeed, all natural tocopherols and tocotrienols have the R configuration at C-2 in the ring. 

The stereoregularity of polymers relates not only to the configuration of four substituents attached to saturated carbon atoms in the polymer chains but also to the geometric isomerism, resulting from the presence of unsaturated carbon atoms in the polymer chains. Such isomerism appears in chains of polymers formed in the 1,4 polymerisation of conjugated dienes [scheme (19)] and the polymerisation of acetylenes [scheme (20)] as well as the ring-opening polymerisation of cycloolefins [scheme (16)] ... 

Horsley et a/.164 have determined a reaction pathway for the geometrical isomerization of cyclopropane by a calculation and search of the full 21-dimensional hypersurface The calculations were performed using a minimal basis set of STO s in a modified SCF calculation using the restricted Hartree-Fock formalism suggested by Nesbet.165 In the region of the trimethylene diradical, a 3 x 3 configuration interaction calculation was included. 

The circular dichroism of cis- and trans- 2-oxazolidinones (59 R = H or Me) has been measured (79T2009). Geometrical isomerism round the exocyclic double bond in 4-(aryl-methylene)-5-(4//)-oxazolones (60), the unsaturated azlactones, is a well-studied phenomenon (75S749). It has been shown by X-ray crystallography (74T351) that the stable form of 4-benzylidene-2-phenyl-5(4//)-oxazolone has the (Z) configuration (61). It isomer-izes to the labile (E) form (62) in polyphosphoric acid and the change is reversed in pyridine. 

Following a close examination of the spectra of geissoschizine and its derivatives,556 71" together with those of several synthetic relatives in which the double bond has the geometrically isomeric (Z) configuration,716 it has been concluded... 

To deal with this problem, we use the E-Z system of nomenclature (pun intended) for cis-trans isomers, which is patterned after the Cahn-Ingold-Prelog convention for asymmetric carbon atoms (Section 5-3). It assigns a unique configuration of either E or Z to any double bond capable of geometric isomerism. 

The formation of an epoxide from an olefin involves concerted bonding of oxygen to both olefinic carbon atoms, for geometrically isomeric open-chain olefins retain their configurations during epoxidation [g]. 

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