Nature Of CH Research Articles

Building Blocks of Crystal Engineering: A Large-Database Study of the Intermolecular Approach between C–H Donor Groups and O, N, Cl, or F Acceptors in Organic Crystals

The nature of CH···X interactions in organic crystals, with X being an electronegative atom, has been the subject of extensive consideration with sometimes contradictory results and ensuing opinions. We perform statistical analysis on large databases of crystal structures retrieved from the Cambridge Structural Database. Crystals containing C–H donors only are considered in conjunction with each of O, N, Cl, or F acceptors in turn. The analysis of Coulombic polarization and dispersion components reveals that the lattice energies of these crystals are largely dominated by dispersive interactions. The frequency of short H···X contacts decreases through the series CHO > CHN > CHCl > CHF, being just sporadic in the latter. The presence of such contacts is positively correlated with the Coulombic contribution to molecule–molecule interaction energies but do not generally determine the pair energy. Short CH···O or CH···N contacts are often relegated to weakly bound pairs; their minor energy contributions might ...

Influence of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH3complexes

AbstractThe effect of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH3(X = F, Cl, Br, OH, H, Me) and NCH···NH3complexes were investigated by quantum chemical calculations. Ab initio calculations were performed using MP2 method with a wide range of basis sets. With tacking into account the BSSE and ZPVE, the values of BEs decrease. Replacement of the nonparticipatory hydrogen atom of HCCH by the electronegative atoms (F, Cl, and Br), lead to the BEs increases. The BE corresponding to the replacement of the nonparticipatory hydrogen atom of HCCH by the OH and CH3groups decreases. A far greater enhancement of the interaction energy arises from replacement of HCCH by the more acidic HCN. The natural bond orbital analysis and the Bader's quantum theory of atoms in molecules were also used to elucidate the interaction characteristics of these complexes. The electrostatic nature of H‐bond interactions is predicted from QTAIM analysis. In addition, the relationship between the isotropic and anisotropic chemical shifts of the bridging hydrogen and binding energy of complexes as well as electron density at N···H BCPs were investigated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Cd xZn 1− xS–arachidic acid composite LB films

Mixed LB multilayers of cadmium arachidate–zinc arachidate (CdA–ZnA) have been exposed to H 2S to form Cd x Zn 1− x S alloy nanoclusters within the multilayers. FTIR and UV–vis spectra of H 2S exposed multilayers showed that the conversion of arachidate salt into arachidic acid (AA) and sulphide formation begins in the first 5 min and is completed in ∼3 h of H 2S exposure. X-ray reflection studies and the nature of CH 2 scissoring band of the composite multilayers show that the formation of sulphide nanoclusters is accompanied by the formation of molecular chain domains with different polymorphic phases of AA, depending upon the relative proportions of CdA and ZnA in the precursor multilayer. Depending upon the CdS and ZnS content, the absorption edge is found to continuously shift from that of pure CdS to that of pure ZnS nanoclusters, indicating the formation of Cd x Zn 1− x S alloy nanoclusters in the arachidic acid matrix. The nanocluster formation is more facile in the mixed archidate multilayers than in pure CdA or ZnA multilayers.

ZnS nanoclusters in LB multilayers

Zinc arachidate (ZnA) LB multilayers have been exposed to H 2S to form ZnS nanoclusters within the layered matrix of arachidic acid (AA). The as-deposited ZnA multilayer consists of arachidate molecules packed in a hexagonal layer cell, with the alkyl chain tilted at about 32° away from the layer normal. FTIR and UV–vis studies show that the conversion of arachidate salt into arachidic acid and the formation of ZnS is completed in 2–3 h. Blue shift in absorption onset and excitonic peak ∼290 nm indicates nanocrystalline nature of ZnS. TEM studies show that ZnS nanoclusters of size ∼5 nm are formed. X-ray reflection and grazing angle diffraction studies and changes in the nature of CH 2 scissoring mode peak of ZnS–AA composite multilayer show that the molecular packing corresponds to a closely packed structure based on orthorhombic subcell in which the chains are tilted by ∼27° towards nearest neighbours. This is in contrast to a loose ‘rotator phase like’ packing of molecules in the precursor ZnA multilayer.

Fundamental Properties and Nature of CH··O Interactions in Crystals on the Basis of Experimental and Theoretical Charge Densities. The Case of 3,4-Bis(dimethylamino)-3-cyclobutene-1,2-dione (DMACB) Crystal

The CH··O contacts in the 3,4-bis(dimethylamino)-3-cyclobutene-1,2-dione (DMACB) crystal have been characterized through a topological analysis of its experimental and theoretical densities, derived from a multipole refinement of X-ray diffraction data and from periodic Hartree−Fock calculations, respectively. The existence or the lack of an H··O bond critical pointthat is a point through the two nuclei where the gradient of the electron density vanishesallows us to distinguish between bonded and nonbonded CH··O contacts, regardless of the value of their H··O separation. The 23 unique bonded contacts in DMACB are characterized by a large and nearly constant (∼140°) C−H−O angle, denoting the importance of the electrostatic energy contribution to such interactions. Instead, the nonbonded ones (four unique for H··O separations up to 3.0 Å) are more bent and may even be folded down to 90°, since their dominant van der Waals contribution to the interaction energy is independent of the C−H−O angle. The CH··O angular distribution observed for H··O separations greater than 2.7 Å is only apparently isotropic, since such isotropy clearly disappears when the bonded and nonbonded contacts are identified and their angular distributions separately analyzed. The Koch and Popelier criteria (J. Phys. Chem. 1995, 99, 9747) to establish H-bonds are, for the first time, applied in their entirety to a large set of CH··O contacts in a crystalline phase. The criteria are always satisfied by all of the bonded intermolecular CH··O contacts, with a single exception concerning one long bond and one of the six criteria only. The expressions proposed by Espinosa et al. (Chem. Phys. Lett. 1998, 285, 170), relating the potential energy densities at the critical point to the H-bond strengths, fail when applied to the weak CH··O interactions present in the DMACB crystal. The reasons for such a failure are outlined and new relationships are proposed. The importance of the promolecular charge distributions in defining topological properties of interest to the CH··O bonds is investigated. The criticism raised by Spackman (Chem. Phys. Lett. 1999, 301, 425) as to the lack of additional information provided by the experimental results to the description of such weak interactions is discussed. It is shown that the promolecular model yields significantly different electron density values at the critical point and in some instances even different topologies, compared to the corresponding multipole or theoretical densities. On the other hand, when the electron density topologies are the same, the values obtained from either electron density for the potential or kinetic energy density at the critical point, are very much alike.

CHTS ROLE WITHIN THE PSYCHOLOGY OF CHU HSI

SUMMARY In this paper we have discussed the various functions which ch'i serves within the psychology of Chu Hsi. We discussed first the differences among human beings which ch'i is said to cause. Various human characteristics were correlated with the qualities of ch'i which were said to determine them. An attempt was then made to determine precisely how ch'i determines these characteristics. It was decided that ch'i‘s causality in this respect can be classified either as direct (as in the case of longevity) or indirect (as in the case of intelligence). By “indirect” it is meant that ch'i determines a given characteristic through its effect upon li which is the direct cause of the characteristic. Indirect causality can further be distinguished as either active (as in the case of moral behavior) or passive (as in the case of intelligence) depending upon the sense in which ch'i can be said to restrain or obstruct li. All of this can be summed up in the following outline. Characteristics determined by ch'i A. Those which ch'i determines entirely, e.g., lifespan B. Those only partially determined by chi 1. Those due to ch'i's action upon li, e.g., moral behavior a. Those due to the conflict of li and ch'i b. Those due to ch'i's reinforcement of li 2. Those due to ch'i's passive obstruction of li, e.g., intellectual ability C. Those for which the nature of ch'i's determination is not specified, e.g., lot in life Then, having looked at ch'i as the cause of differences within species, it was argued that Chu Hsi believes that ch'i is responsible for all differences among the ten thousand things, differences between species as well as within them. Finally, the two basic types of ch'i, yin-ch'ibl and yang-ch'ibm were discussed in the course of an explanation of how ch'i tself is capable of variation. Therefore, it was concluded that the basic function of ch'i within the psychology of Chu Hsi is to account for difference, all difference. Basically, we can say that this is ch'i‘s most important function within the philosophy of Chu Hsi as a whole. For within his philosophy, psychology is much more important than metaphysics, although we must immediately add that Chu His takes pains to ground the former upon the latter. Speaking in the most general terms, it must be admitted that Chu Hsi is not so much concerned with elucidating the characteristics of “being as such” as he is concerned to explain “being as human.”

A CH star in the globular cluster M22, and the nature of CH and CN anomalies

A CH star in the globular cluster M22, and the nature of CH and CN anomalies

The Nature of Ch'an (Zen) Buddhism

The Nature of Ch'an (Zen) Buddhism