Conformational demands

Other aldohexoses behave similarly m adopting chair conformations that permit the CH2OH substituent to occupy an equatorial orientation Normally the CH2OH group is the bulkiest most conformationally demanding substituent m the pyranose form of a hexose... 

Due to the high conformational demands which are imposed on higher-order cycloadditions, fulvenes, heptafulvenes and tropones have been mostly applied in uncatalyzed [6 + 4] cycloadditions. The scope of metal-promoted cycloadditions, however, is much broader due to the preorganized orientation of the reactants which are both co-ordinated to the metal center. 

It is obvious that a different factor must be found to explain the sensitivity to dimer formation for maximum water content in the monomeric surfactant aggregates because this phenomenon Is entirely outside the realm of polymers and their entroplc conformational demands. One such factor is the Interaction between aromatic compounds and the polar group of a surfactant. Two examples of such Interaction are described In the next section. 

The Interaction between polymers and the colloidal droplets In mlcroemulslons results In space conflicts due to the entroplc conformational demands by the polymer. This Is a serious problem as Is evident by a multitude of systems which has shown phase separation during polymerization. However this Interaction Is not the only one of Importance for the polymer/mlcroemulslon system. An aromatic dimer has been shown to also have a strong Influence on the mlcroemulslon region even though Its conformation variation does not exist. 

Sections 12.1 and 12.2 described the E2 reaction of acyclic alkyl halides. Elimination also occurs with cyclic halides, but the conformational demands of the ring must be taken into account (see Chapter 8, Section 8.5). The E2 reaction must proceed by an anti transition state, which imposes additional conformational demands on ring compounds. 

In one chair conformation, the leaving group occupies an axial position. In the other chair conformation, the leaving group occupies an equatorial position. The requirement for an periplanar conformation demands that an E2 reaction can only occur from the chair conformation in which the leaving group occupies an axial position. To see this more clearly, consider the Newman projections for each chair conformation ... 

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