C-H- S contacts

The nonplanar nature of 11 hinders intermoleeular contacts between the metal dithiolene complexes. Thus, there are few intermoleeular interactions between the anions within [Et4N][ll], although short C-H -S contacts of 2.906 A are observed between the pendent thiophenes of neighboring anions (Figure 13A). In contrast, the more planar structure of 12 allows significant jt stacking of the complexes to form columns with a face-to-face distance of 3.7 A (Figure 13B). ... 

The principal values, 6n, 622, 633, of the chemical shift tensor were obtained for each form by CP/MAS NMR experiments. The orientation of the principal axes with respect to the molecular frame was investigated by P CP/single-crystal NMR for the complex with propan-2-ol. The principal axis 1 of both chemically equivalent phosphorus atoms is nearly parallel to the P-S bond and the principal axis 3 is very close to the P=S bond. The comparison of experimental P 6 parameters with theoretical data calculated by the DFT GIAO approach provided complementary information about the most sensitive NMR parameters, which best characterize the nature of the C-H -S contacts. 

Besides the C H- O interactions, the most relevant C-H- X interactions are the C H- N, C H- S and C-H- TT interactions (see Table 8 for a complete set of results). The trends for the C H- -N contacts found in crystals were first analyzed by Taylor and Kennard [72] in their seminal paper, where they also concluded that there was enough evidence to consider them as hydrogen bonds. These authors also attributed a hydrogen bond nature to the C H- -N and C H- -S contacts. 

The role of weak intermolecular interactions in the formation of inclusion complexes is one of the most challenging questions. From the analysis of chemical shift tensor (CST) parameters, conclusions regarding strong and weak hydrogen bonding can be drawn. In particular, weak hydrogen bonds have recently attracted much attention as important structural elements of complex architecture [36]. In all structures of DGTD complexes, intermolecular C-H-S=P contacts were observed (see [33] for details). 

The influence of Pl-S-H-C forces on P NMR shielding parameters considering thiolo sulfur was discussed earlier. Analysis of the data proved that the influence of this type of interaction on P NMR shielding is much smaller compared to the analogous thiono S -CH4 contacts. It was concluded that the most sensitive parameter, which characterizes the C-H-S weak contacts, is span Q parameter defined as 033-011. 

The oldest sohd acid used is Nafion-H (Olah, Keumi, Meidar, 1978). In this case, the reaction between carboxylic acid and alcohol is run at T > 95 °C ( 5 s contact time), obtaining a high reaction yield. 

Golovanov, D. G. Lyssenko, K A. Antipin, M. Y. Vygodskii, Y. S. Lozinskaya, E. I. Shaplov, A. S. (2005). Extremely short C-H "F contacts in the l-methyl-3-propylimidazolium SiFe - the reason for ionic "liquid" unexpected high melting point. Crystengcomm, 7, 53-56. 

Dicyclohexylarnine may be selectively generated by reductive alkylation of cyclohexylamine by cyclohexanone (15). Stated batch reaction conditions are specifically 0.05—2.0% Pd or Pt catalyst, which is reusable, pressures of 400—700 kPa (55—100 psi), and temperatures of 75—100°C to give complete reduction in 4 h. Continuous vapor-phase amination selective to dicyclohexylarnine is claimed for cyclohexanone (16) or mixed cyclohexanone plus cyclohexanol (17) feeds. Conditions are 5—15 s contact time of <1 1 ammonia ketone, - 3 1 hydrogen ketone at 260°C over nickel on kieselguhr. With mixed feed the preferred conditions over a mixed copper chromite plus nickel catalyst are 18-s contact time at 250 °C with ammonia alkyl = 0.6 1 and hydrogen alkyl = 1 1. 

As mentioned in the Introduction, in iron—sulfur proteins, the hyperfine shifts of the nuclei of the coordinating cysteines are essentially contact in origin (21, 22). In the case of [Fe4S4l (17) and [FegS4] (112) cluster, it has been shown that the hyperfine shift of the cysteinyl H/3 and Ca nuclei can be related to the value of the Fe-Sy-C/S-H/S/Ca dihedral angle (6) through a Karplus-type relationship of the form... 

Since the best results were obtained with the W and W-based oxide catalysts, the reaction was studied in more detail using 20 g portions of these catalysts. The reaction was performed at 230°C, with feed rates of pyruvic acid, air, and water = 10.5, 350, and 480 mmol/h. The contact time defined as volume of catalyst (ml)/rate of gaseous feed (ml/s) was about 5.2 s. The main products were citraconic anhydride and CO2. The amount of acetic acid was very small. No other products were detected except for very small amounts of CO, acetone, and acetaldehyde. A relatively large discrepancy was observed between the amount of consumed pyruvic acid and that of the sum of produced citraconic anhydride and acetic acid. This discrepancy was defined as "loss". 

Fig. 7 Packing diagrams of (a) [(ppy)Au(C8H4S8)]2[PF6] (PF6 salt) and (b) [(ppy)Au(C8H4 S602)]2[BF4] (BF4 salt) viewed along the a axis. Side-views of the columns in the (c) PF6 salt and (d) BF4 salt. Molecular arrangements of two crystallographically independent molecules within the column of (e) PF6 salt and (f) BF4 salt. Fine lines indicate S—S contacts shorter than 3.7 A. Dashed lines indicate O—H contacts within the range of 2.62-2.70 A. (Reprinted with permission from [35]. Copyright 2008 American Chemical Society)...

SAM-covered gold surfaces, these three peaks were assigned to Au-S, C-C, and C-H modes of surface-bound alkanethiolates [30]. The absence of a strong S-H signal at 329 mV suggests that most of the thiol groups have reacted with the gold bottom and top contacts. Peaks are also reproducibly observed at 80, 107, and 186 mV. We note that all alkanethiolate peaks, without exception or omission, occur in the spectra. 

Ichikawa, H., Armstrong, R.B. and Harber, L.C. (1981). Photoallergic contact dermatitis in guinea pigs improved induction technique using Freund s complete adjuvant. J. Invest. Dermatol. 76 498-501. 

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