Staggered position

Appllca.tlons. The first widely appHcable Ic separation of enantiomeric metallocene compounds was demonstrated on P-CD bonded-phase columns. Thirteen enantiomeric derivatives of ferrocene, mthenocene, and osmocene were resolved (7). Retention data for several of these compounds are listed in Table 2, and Figure 2a shows the Ic separation of three metallocene enantiomeric pairs. P-Cyclodextrin bonded phases were used to resolve several racemic and diastereomeric 2,2-binaphthyldiyl crown ethers (9). These compounds do not contain a chiral carbon but stiU exist as enantiomers because of the staggered position of adjacent naphthyl rings, and a high degree of chiral recognition was attained for most of these compounds (9). 

The conformational dynamics of chain segments near the head groups is more restricted than that of those far from the micellar core [8]. Moreover, to avoid the presence of energetically unfavorable void space in the micellar aggregate and as a consequence of the intermolecular interactions, surfactant molecules tend to assume some preferential conformations and a staggered position with respect to the micellar core [9]. A schematic representation of a reversed micelle is shown in Figure 1. 

The needles of the paraffin wax are typical of many organic crystals in which the molecules are in staggered position to each other as in Type I of Figure 9. The plate type is the side-by-side alignment of the molecules (66). 

The conformational energies and helix parameters are calculated for the various states of polymethylphenylsilylene chain. The calculations are performed for the three different relative dispositions of the phenyls attached to three successive silicon atoms. The minima are invariably shifted from perfectly staggered positions. 

Nearly all side-chain prediction methods depend on the concept of side-chain rotamers. From conformational analysis of organic molecules, it was predicted long ago [157, 158] that protein side chains should attain a limited number of conformations because of steric and dihedral strain within each side chain and between the side chain and the backbone (dihedral strain occurs because of Pauli exclusion between bonding molecular orbitals in eclipsed positions) [159]. For sp3-sp3 hybridized bonds, the energy minima for the dihedral are at the staggered positions that minimize dihedral strain at approximately 60°, 180°, and —60°. For sp3-sp2 bonds, the minima are usually narrowly distributed around +90° or —90° for aromatics and widely distributed around 0° or 180° for carboxylates and amides (e.g., Asn/Asp y2 and Glu/Gln /3). 

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