Cylindrical molecules

The amphipathic compounds shown in Scheme 2 can form a disc-like micelle(7). The shape of a molecular aggregate depends on the shape of the constituent molecules(8). For instance, conical molecules with large polar head groups prefer to form spherical micelles while cylindrical molecules tend to give flat aggregates. Trans-azobenzene is a rod-like molecule whereas the cis-form is bent. 

Fig. 6a,b. Height micrographs obtained by tapping mode SFM from monolayers of a spherical b cylindrical molecules adsorbed on mica [84]. Top self-assembly of monodendron side groups into spherical and cylindrical supramolecular dendrimers. The process depends on the degree of polymerization of the polystyrene main chain... 

SFM length of the cylindrical molecules per repeat imit of the main chain determined from the SFM micrographs as Lspm = M x L /Mn. 

FIGURE 5.7 The instantaneous dipole moments in two neighboring cylindrical molecules tend to be close together and interact strongly. Those on neighboring spherical molecules tend to be far apart and interact weakly. 

The molecular symmetry number (a) is a measure of the rotational degeneracy of the molecule. It is defined as the number of indistinguishable positions that can be obtained by rigidly rotating the molecule about its center mass. Symmetry numbers for spherical, conical, and cylindrical molecules, shapes with infinite axes of rotation, have o values of approximately 200, 20, and 20, respectively. Chemicals with no axes of symmetry have o = l. 

If dendrimers are introduced on stiff backbone polymers cylindrical molecules are created and an empty inner volume becomes available between the stiff backbone and the outer dendrimer shield. Furthermore the peripheral groups of the dendrimer can be manipulated to control the solubility characteristics of the resulting polymers. 

In Chapter 3, such a coding shall be introduced for "cylindrical" molecules. 

Next, observe that in all of the cylindrical molecules nomenclated so far, the chains between the bridgehead atoms are "independent" i.e., there is no atom common to two or more chains between the bridgehead atoms. On the other hand, had there been such "cross-linkage" in three dimensional space then the "jump rope effect" between the individual chains would be... 

Fig. 4 Comparison of "Similar" Names - A Theoretical "Cylindrical" Molecule...

The order parameters S for all three molecular axes or alternatively, the combination S plus D describe on the level of the first relevant polynomial term the orientational distribution of a rigid, non-cylindrical molecule in the uniaxial nematic phase. Additional order parameters come into play for biaxial phases (Straley, 1974). A concise overview on the concepts from statistical mechanics relevant to order parameters was given by Zannoni (1979). 

In several respects, the cylindrical molecule ferrocene (di( 7 -cyclopentadienyl)iron, FeCpj) is analogous to the planar molecule benzene (CgHg). Both ferrocene and benzene are electron-rich aromatic systems that undergo electrophilic substitution. Ferrocene reacts about 10 times faster than benzene in Friedel-Crafts acetylation and about 10 times faster in mercuration with Hg(OAc)2-... 

As discussed by Israelachvili (1992), the shapes of surfactant aggregates can, to a first approximation, be anticipated based on the packing of simple molecular shapes (Tanford 1980). Figure 12-1 from Israelachvili illustrates this principle Conical molecules with bulky head groups attached to slender tails form spherical micelles cylindrical molecules with heads and tails of equal buUdness form bilayers and wedge-shaped molecules with tails bulkier than their heads form inverted micelles containing the heads in their interiors. A simple dimensionless molecular parameter that controls the shape of the aggregates is the molecular shape parameter here v is the volume occupied by the hydrocarbon... 

For cylindrical molecules of length 2b and radius a, we have if b is much larger than a, may be approximated by ... 

The validity of (3.2.9) is restricted to the symmetries mentioned above, that is to cylindrical molecules, macroscopically uniaxial samples, and r] = 0. For many samples, these conditions are fulfilled when using NMR, because the quadrupole coupling tensor of aliphatic deuterons is often found to be axially symmetric. In wideline NMR, the anisotropy of the magnetic shielding is used. Here the angular resolution is lower, and the calculation has to be extended to include p > 0 [Henl]. In combination with MAS (cf. Section 3.3), the Legendre subspectral analysis has been used successfully for the determination of molecular order in partially ordered polymers [Harl]. 

Due to lack of free rotation around the bonds connecting the glucopyranose units, the CDs are not perfectly cylindrical molecules but are toroidal or cone shaped. Based on this architecture, the primary hydroxyl groups are located on the narrow side of the torus while the secondary hydroxyl groups are located on the wider... 

Fig. 14.14. The influence of molecular rotation on the structures of the paraffins (a) the orthorhombic structure (b) the hexagonal structure of close-packed cylindrical molecules.

The rods are long enough. The molecules can be cylindrical, semi-sphero-cylindrical or even lathe. The basic conclusions for these molecular shapes are quite similar. In the text below, only the solutions of cylindrical molecules are described. The calculation can be easily extended to deal with disc-like molecules by varying the length-to-breadth ratio. 

Fig. 7.2.1. The laboratory-fixed axes are XYZ and the molecule-fixed axes are X Y Z . The orientation angles of the symmetry axis (X axis) of the cylindrical molecule are given by 0 and 0.

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