C-H 7t interactions

The structure of the 1 1 methanol solvate of olanzapine has been reported, where pairs of olanzapine molecules form a centrosymmetric dimer by means of C—H—-7t interactions [66]. The solvent molecule was linked to the drug substance through O—H-N, N—H O, and C—interactions. In a new polymorph of the 1 1 dioxane solvatomorph of (+)-pinoresinol, the structure was stabilized by O—H O hydrogen bonds between the compound and the solvent [67], Two new polymorphs of 2-cyano-3-[4-(/Y,jV-diethylamino)-phenyl]prop-2-enethioamide and its acetonitrile solvatomorph have been characterized [68], Although crystallization of the title compound was conducted out of a number of solvents, only the acetonitrile solvatomorph could be formed. 

C—H 7t Bonds. Even weaker hydrogen bonds, never more than 4 kJ mol 1 (1 kcal mol-1), can be detected between C—H bonds and C=C n bonds. These interactions are seen in solid-state structures like that of benzene with its edge-to-face arrangement 2.94, and in some noticeable upfield shifts in the -NMR spectra on changing solvents from carbon tetrachloride to benzene. Larger shifts in the NMR spectra are seen with the more acidic C—H bonds, with chloroform showing an upfield shift of 1.35 ppm at infinite dilution, because of the formation of a bond to the centre of the n system 2.95. 

Figure 4-6. The interactions of (—)-HA with the active site of TcAChE. (a) The hydrogen bonding networks. The water molecules are represented by red balls, (b) The C—H... 7t hydrogen bonds. The distances are given in angstroms. Copy from Ref. 10.

Figure 3.9.15 Layered supramolecular structure mediated by Sn...7t and C-H... it interactions in the structure of 21...

Fig. 16. The different styles of packing in the crystalline state of some aminophenols [44-46]. It is shown that p-aminophenol utilizes 0-H---N and N-H---0 hydrogen bonds in crystal packing, while the o- and m-compounds and 2-amino-4-methylphenol also utilize C-H- -O and N-H - 7T interactions...

N-H - 0, C=0- H-Osoivent, 0-H---0, N-H - 0=C hydrogen bonds and C=0- Jt, C-H- 7t, and it - it stacking interactions, derived from both Schiff base and rednced Schiff base ligands are discussed to provide the readers with some nseful insights into the factors behind the observed strnctnral diversity that direct the formation of snpramolecnlar strnctures in the solution and/or solid state. 

Figure 23 Structural mimicry in diarylethynylmethanol derivatives. (a) Generic chemical structures when Y = methyl, the molecule is bis(4-tolyl)ethynylmethanol, and when Y = chloride, the molecule is bis(4-chlorophenyl)ethynyhnethanol, (b) for Y = methyl, dimeric aggregate based on O-H- -ji interactions, and supramolecular chain based on ethynyl-C-H- -ji interactions, and (c) for Y = chloride, dimeric aggregate based on ethynyl-C-H- -n interactions, and supramolecular chain based on O-H- - -7T interactions. The O-H- - -n and C-H- - -ji interactions are shown as purple dashed lines.

For /8-substituted 7t-systems, silyl substitution causes the destabilization of the 7r-orbital (HOMO) [3,4]. The increase of the HOMO level is attributed to the interaction between the C-Si a orbital and the n orbital of olefins or aromatic systems (a-n interaction) as shown in Fig. 3 [7]. The C-Si a orbital is higher in energy than the C-C and C-H a orbitals and the energy match of the C-Si orbital with the neighboring n orbital is better than that of the C-C or C-H bond. Therefore, considerable interaction between the C-Si orbital and the n orbital is attained to cause the increase of the HOMO level. Since the electrochemical oxidation proceeds by the initial electron-transfer from the HOMO of the molecule, the increase in the HOMO level facilitates the electron transfer. Thus, the introduction of a silyl substituents at the -position results in the decrease of the oxidation potentials of the 7r-system. On the basis of this j -efleet, anodic oxidation reactions of allylsilanes, benzylsilanes, and related compounds have been developed (Sect. 3.3). 

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