H-jt interaction

This [2]catenane is composed of a jt-electron-deficient tetracationic cyclophane interlocked with a Jt-electron-rich macrocyclic polyether. In addition to a mechanical bond, [jt Jt] stacking interactions between the complementary aromatic units, [C-H---0] hydrogen bonds between the a-bipyridinium hydrogen atoms and the poly-ether oxygen atoms, and [C-H---Jt] interactions between the 1,4-dioxybenzene hydrogen atoms and the p-phenylene spacers in the tetracationic cyclophane hold the two macrocyclic components together and control their relative movements in solution. As a result of the asymmetry of the tetracationic cyclophane, two transla-... 

Figure 3.9.10 Layered supramolecular structure mediated by Sn...it and C—H...jt interactions in the structure of 15...

C-H Jt interaetions are moderate but nevertheless important interactions that contribute to protein stability (Brandi et al., 2001). Modeling studies illustrated in Eigure 2.9 suggest that F3.25(190) has a C-H jt interaction with the C5-C6 double bond in the AEA acyl chain. This interaction is consistent with a recent mutation study which showed that a E3.25(190). A mutation resulted in a 6-fold loss inaflinity for AEA [CBj WTKj = 0.3 pM(0.1-0.6) CBj E3.25A = 1.8 iM... 

X-H---jt interactions possess numerous characteristics usually attributed to hydrogen bonds but it is also possible to indicate features typical only for them [1]. These interactions are the subject of extensive studies since they play the key role in various chemical, physical and bio-chemical processes, similarly as the... 

Hexaarylbenzenes combine design elements of the inclined aromatic plane (Section 4) and the hexa-host (Section 5.1) strategies. These clathrands are able to include terminal alkynes by ntilizing multiple C-H- -Jt interactions (including the sp C-H- -Jt motif). This outcome is illustrated in Figure 26 for the case of the clathrate formed between hex-amethylbenzene 98 and phenylethyne. ... 

Peptide X-H...jt interactions are fimctional in stabilization of helix termini, strand ends, strand edges, 8-bulges, and regular turns. Side-chain X-H...7T hydrogen bonds are formed in considerable numbers in a-helices and j8-sheets [205]. The conformational influence of N - H...n and O -in organic molecules and also their role in crystal packing have been established [206,207]. The study on C- interactions has clearly established... 

The non-bonded contact to be searched was set up as the one occmring between the ring centroid (Cg) and the interacting hydrogen and donor atoms. This was allowed to be an intermolecular interaction up to a distance of 4.0 A for D (donor...Cg) and 3.0 A for d (H...Cg) distances. The lower limit for interactions with Cg was set at 2.8 and 1.8 A, respectively for D and d distances. To ensure the data analyzed had a suitable degree of accuracy, further criteria were used to include only hits with 3D coordinates, without metals and no disorders. For statistical equivalence, the crystallographic discrepancy factor was varied for each dataset (Rf < 0.10 for isoxazole indole and Rf < 0.05 for imidazole). Since there were no hits for S - H...jt interaction, further analyses were restricted to O - H, N - H, and C-H donor species. 

Figure 1.16 shows the optimized structures of the transition states of two competing pathways for the double bond coordination. Since both TS s lead to the formation of the chelate cycle in the less hindered quadrant, the relative stability of TS21 is evidently stipulated by C-H... jt interaction between the substituted phenyl ring of the substrate and the t-Bu substituent of the catalyst, similar to that experimentally detected in the corresponding square planar catalyst-substrate complex. This conclusion is in accord with the experimentally observed increase of the optical yield of the asymmetric hydrogenation in a series 13<123<124, although we were unable to reproduce this effect computationally. 

In the case of the t-butyl-substituted enamide 16, the a-dihydride pathway is disfavored due to the impossibility of the C-H... jt interaction and significant steric hindrance between the two adjacent t-Bu groups. 

The calix[6]arene derivatives are capable to form pseudorotaxanes (Fig. 38.21) [45, 46]. In both complex the calixarene molecules are richly decorated with four types of substituents of different chemical properties enabling formation of C-H - 0, C-H N and C-H - Jt interactions between host and guest. 

However, in 7, the unsolvable orientation of dibenzofuran molecules along their short axis in the cociystal results in a disorder structure, which is not observed in 8. The adjacent zigzag chains were further united by C-H- Jt interaction in 7 and C-H- I, C-H- -F contacts in 8, which should contribute to maintain the stability of the 3D structure of the cocrystals. 

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