Structural considerations

Structural Considerations.—The crystal structure of the asymmetrically substituted cis, trans-2,5-di-t-butylcyclohexyl toluene-p-sulphonate (l)has been determined. The mean torsion angle of the cyclohexane ring in (1) is 55.1°, slightly less than the value of 55.9° for cyclohexane. Newman projections along the C-2—C-7 and C-5—C-11 bonds 

The crystal structure of (4), derived from (5) by sequential borohydride reduction and acetylation, has been determined. The phenyl group is oriented with its flat side towards the axial hydrogens on the same side of the cyclohexane ring. However, a 

The crystal and molecular structure of 2-(a-p-bromophenyl-P-nitro)-ethyl-5-methylcyclohexanone (6), a product from reaction of l-morpholino-3-methylcyclo-hexene with p-bromo-P-nitrostyrene, has been determined. Although a cis-configu-ration was anticipated on a mechanistic basis, the n.m.r. spectral analysis did not provide an unequivocal answer. X-Ray analysis indicated a chair cyclohexanone ring with the methyl group axial and the substituted ethyl group equatorial. 

The crystal structures of the hexameric cyclohexyl-lithium and trimethylsilyl-lithium have been determined. In the latter molecule each McjSi group is located centrally above a triangular face on the periphery of the Li ring, whose conformation is regarded as a folded chair (7). 

Structural Considerations.—Crystallography. An A -ray diffraction study of 1-aminocyclohexane carboxylic add has shown the carbonyl group to be axially oriented in the solid. This contrasts with an equatorial disposition of the carboxyl reported earlier by the same authors for the amine hydrochloride. Possible distortions caused by the steric bulk of a t-butyl group have been examined by James and 

Lectard, A. Lichanot, F. Metras, J. Gaultier, and C. Hauw, Cryst. Structure Comm., 1975, 4, 527. S. R. Holbook and D. Van der Helm, Acta Cryst., 1975, B31,1689. 

Miravitlles, and M. Font-Altaba, Acta Cryst., 1975. B31, 2510. 

The auto-oxidation product of 4,6-di-t-butyl guaiacol has been shown to be 5,6-epoxy-4-hydroxy-2-methoxy-4,6-di-t-butylcyciohex-2-enone (2) by a further direct methods 2f-ray diffraction study. The hydroxy-group and the epoxide moiety are cis as indicated. The cyclohexenone ring is held in a boat conformation by two intermolecular hydrogen bonds formed between epoxide and hydroxy on adjacent molecular pairs present in the lattice. 

X-Ray structures of (+)- and (- -)-traos-ip-carboxy-8P-hydroxy-la,4a,6P-tri-methyl-5-oxodecahydronaphthalene lactone (4) have been determined using direct methods. The cyclohexanone present has a twist conformation with a quasisymmetry axis while the five-membered ring is somewhat puckered. In (4) the absolute configuration of C-6 was confirmed as S, given the known configurations of the 

In this section the methods which have been used to gain structural information are briefly summarized. The term structure is used in this context in its broadest sense, including more qualitative observations concerning the skeleton of the bridging atoms. As a general rule, the hydroxo-bridged polynuclear complexes of chromium(III) and cobalt(III) can be isolated as well-defined crystalline salts and it is therefore quite natural that single-crystal X-ray structure analysis has 

The X-ray crystal data are often used in relation to solution chemistry, and the general question of the identity of the species in solution and those present in the crystals has to be considered, since rapid interconversion between different bridged species is frequently seen for both chromium(III) and cobalt(III). Supplementary solution measurements are therefore generally required in order to be reasonably certain that the solid-state structure corresponds to the structure in solution. 

The most important methods for obtaining structural information about solutions are probably potentiometric pH measurements and visible/ultraviolet spectroscopy, but many other techniques have been applied, including bridge-cleavage experiments, magnetic measurements, and electron spin resonance (ESR) spectroscopy (22, 23). 

Hydrolysis is strong acid in which all hydroxo bridges are cleaved, followed by identification of the various mononuclear species and a determination of their molar ratios, may provide extremely valuable information. A straightforward example is the cleavage of the tetra-nuclear species Cr4(NH3)12(OH)66+, which yields Cr(H20)63+ and cis-Cr(NH3)4(H20)23+ in a ratio of 1 3 (40). Since it could be demonstrated at the same time that the polynuclear cation does not exhibit acid base properties in the pH region for terminally coordinated water, it was concluded that the only possible structure was 6 in Fig. 1, as later confirmed by a crystal-structure analysis (41). 

In the dinuclear complexes two octahedrally coordinated metal ions are bound together by one, two, or three hydroxide ions by sharing a corner, an edge, or a face, as shown in structures 1-3. These mono-, di-, and trihydroxo-bridged binuclear structures are known for 

an ability to self-organize from solution to form proper structural order in the solid state for charge transport, and 

a resistance to adverse environmental effects, particularly degradative interactions with atmospheric oxygen. 

Most current solution-processable organic semiconductor compounds fail to satisfy all these requirements simultaneously. 

The plant layout designer should be aware that pre- ast concrete pipe racks require structural members hat are mudi larger than most designs. Exhibit 11-25 llustrates a precast column with an embedded steel 

Such equipment as drums and deaerators is often located above pipe rack columns. To avoid wasting valuable rack space with the large support columns, the inside face of the pipe rack column must line up with the inside face of the equipment support column, as shown in Exhibit 11-26. This approach also allows the feed-water outlet piping to run venically down to the pump before the expansion loq is added. 

Fireproofing of pipe rack columns is shown in Exhibit 11-27. If hydrocarbons are prevalent, it is common to fireproof the columns to a level just below the lower rack supp ort beam. If air coolers or other equipment is located above a pipe rack, the fireproofing is extended to the equipment support beam. This issue must be reviewed with the client allowances may need to be made for as much as 4 in (100 mm) of fireproofing. 

EXHIBIT 11-25 Precast Concrete Pipe Rack Considerations 

A non-chair conformation of the cyclohexyl ring in cis-2,trans-3-6ibromo-cis-4-t-butylcyclohexyl p-nitrobenzoate (3) has been found in an X-ray structural study of the molecule. In the solid a twist conformation with a staggered t-butyl group and ester moiety in pseudo-equatorial positions exists the bromine atoms are located in 

Investigation of the hexachlorocyclohexane configurational isomers has continued. The structure of the y-isomer (of the seven known configurational isomers this is the only one which is a useful insecticide, known as Lindane or Gammexane) is confirmed as 1,2,3,4,5,6-hexachlorocyclohexane. The jS-isomer, also re- 

Schaumann, S. Harto, and G. Adiwidjaja, Angew. Chem. Internal. Edn., 1976,15,40. 

The configuration of the major 1,4-diol isomer from the lithium reduction of 4-hydroxy-2-t-butyl-3-methyl-2-cyclopentenone has been determined and shows the ring to be almost half-chair in form with a binary axis passing through C-3 and bisecting the C-1 and C-5 segment. 

The crystal and molecular structure study of cis-l-oxa-7,7,10-trimethyldecahne-2,5-dione has shown that the a priori most stable steroid conformation (10a) exists in the solid. Perhaps surprisingly the a priori less stable form (10b) is observed (n.m.r.) in solution. A direct-methods study of cis- and trans-9,10-his(trimethylsilyl)-9,10-dihydroanthracene has been made. In the former the central ring is a deformed boat, in the latter a deformed chair. 

The barium atoms in these structures have a cubeoctahedral coordination of oxygen atoms. The oxygen atoms can be grouped into five kinds  

A comparison of the short Nb-Nb interatomic distances in compounds with condensed clusters is given in Table 5. There seems to be a correlation between the number of valence electrons available per two-electron three-center bond and the average Nb-Nb bond length in the NbeOn clusters (Fig. 21). The average Nb-Nb bond length is 287 pm in BaNbsOs with 1.37 electrons per three-center bond whereas t Nb- Nb = 297 pm in NbO with 1.13 electrons. It must, however, be remembered that in all compounds there is a balance between A-O, Nb-O, 0-0, and Nb-Nb distances. The two types of niobium atom in the condensed clusters give rise to three kinds of Nb-Nb bonding Nb -Nb Nb -Nb and Nbi l-Nb J and as a result the Nbe octahedra are always distorted. The 

Compound Nb-Nbave Intra NbO block Inter NbO block NbW-NbW NbW-Nbl l NbM-NbS I Ref. 

In this short review it is not the intention to discuss all compounds with condensed NbeOn clusters in detail, however, there are two pairs of compounds which we find 

Penicillins (1) and cephalosporins (2) of either natural or semi-, partly or totally nthetic origin have in most cases two fundamental units, the penam (3) [4] and cepham (4) [5] systems. 

Tlie names penam and cepham or cephem are widely used and are applicable to most of the natural or semi-synthetic derivatives [6] without difficulties. In the case of nuclear analogues, however, this nomenclature causes various problems. In order to solve this question, Bose [7] has suggested a nomenclature for fused /3-lactams. Keeping the unofflcial numbering, he gave the generic names heptam (5), octam (6), nonam (7) and decam (8) to these bicyclic systems. 

For bicyclic /3-lactams of other types he suggests the names neoheptam (9), neooctam (10), etc. In this neo -series the suggested numbering system is based 

The situation is actually more complicated. Further neutron diffraction studies on NASICONS with x = 1.85-1.9 revealed that the Na-I site is about i occupied, the Na-II site is filled and the Na-III site, which lies along the conduction pathway displaced towards Na-I, contains the remainder ( 1.7-1.8) of the sodium ions. The distance between Na(l) 

The essential correctness of the situation was confirmed by single crystal studies The crystals were grown over a four-month period at 1200 °C and therefore reached an equilibrium composition very close to Na3Zr2Si2POi2. The maximum in conductivity is thus correlated with maximum occupancy of the mid-sodium site. The conduction process is thought to be accompanied by a breathing-like motion of the framework in agreement with the dynamic disorder observed in the crystals Space does not permit a detailed discussion of this dynamic disorder or the controversy concerning the stoichiometry of NASICON but the reader is referred to references 41 and 51 for more information on these subjects. 

It is evident from our discussion that very little work has been carried out on the proton phases of NASICON. However, with the background given here it should be apparent that such phases are extremely interesting as solid electrolytes and deserve further study. 

Alberti in Inorganic Ion Exchange Materials, A. Clearfield (ed) (CRC Press, Boca Raton, FI. (1982)), 98. 

Subramanian, P. R. Rudolf and A. Clearfield, J. Solid State Chem. 60 

Polyphosphates crystallized in an ultraphosphate melt may be superlong chains of linear molecules with only defect cross-linking. Also, cross-linking may be contained in an amorphous phase, where it is very difficult to detect directly, rather than as a part of a crystal structure. Cross-linking is probably a random event and does not constitute a thermodynamically stable state, even in the absence of moisture. 

Pfansteil and Her demonstrated that as the K2O-P2O5 ratio is reduced from 0.998, the influence of cross-linking in solutions of Kurrol s salt diminishes, if it is not eliminated entirely. The behavior expected for very long linear chains persists after the expected behavior for cross-linkages is gone, as judged from viscosities of aqueous solutions obtained from salts with K2O--P2O5 ratios well below 0.98. 

The crystal structure analyses of trans- and cis-sulphonate esters (2) and (4) 

In a crystal structure investigation of cis-2-chloro-4-t-butylcyclohexanone (6) the t-butyl group was found to be off-staggered to the extent of 1.5°, a value 

Further structure determinations of cyclohexane compounds have been carried out by X-ray analysis. The crystal and molecular structure of (7) was determined in part for identification purposes. The bond length of the exo-cyclic C-4—C-7 bond was found to be 1.55(1) A. The structure determination of (8) indicates that both bromine and phenyl are axial and that the benzene rings are inclined to each other at an angle of 37.5° in the solid state. 

X-Ray analysis indicatedthat the potassium salt of trans-cyclohexane- 

4-dicarboxylic acid has the formula C8H10O4K2. The same grouphas also determined the crystal structure of trans-cyclohexane-l,4-dicarboxylic acid. cis-l,3,5-Trichlorocyclohexane, a cyclic form of poly(vinyl chloride), has been shownby X-r y analysis to have all three chlorine atoms equatorial with bond angles within + 3.7° and —1.3° of the tetrahedral value the mean C—C bond length is 1.513 A and the mean C—Cl bond length is 1.805 A. 

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Structural Considerations. Sdos, bins, and hoppers fail, in one way or another, each year. The causes of silo failures are many and varied (9). Such failures can range from a complete and dramatic stmctural coUapse, to cracking in a concrete wall, or denting of a steel shell. This last is often a danger signal indicating that corrective measures are required. 

VllI, Damage slight in well-built structures considerable in ordinary substantial buildings with some collapse. Jamage... 

Transition elements, for which variable valency is energetically feasible, frequently show non-stoichiometric behaviour (variable composition) in their oxides, sulfides and related binary compounds. For small deviations from stoichiometry a thermodynamic approach is instructive, but for larger deviations structural considerations supervene, and the possibility of thermodynamically unstable but kinetically isolable phases must be considered. These ideas will be expanded in the following paragraphs but more detailed treatment must be sought elsewhere. " ... 

Minimum size of pipe is, sometimes dictated by structural considerations, i.e., l/i-inch Schedule 40 steel pipe is considered the smallest size to span a 15 to 20 pipe rack without intermediate support. 

Small-Particle Effects and Structural Considerations for Electrocatalysis Kinoshita, K. 14... 

The thiohalides MoSX are diamagnetic (269). In Mo4S4Br4, molybdenum transfers 12 electrons to the anions, and 12 electrons remain for the cluster M04, forming a doublet for each edge of the M04 tetrahedron (269). The diamagnetism of the compounds of the type MogCligSe can be interpreted in a similar way (273) from structure considerations. These compounds have been found to be dielectric (273). 

Evidence is provided by this analysis that (a) structural considerations discriminate among at least four practical classes of pi delocalization behavior, each of which has limited generality (b) the blend of polar and pi delocalization effect contributions to the observed effect of a substituent is widely variable among different reaction or data sets (the contributions may be opposite as well as alike in direction), depending upon structural considerations and the nature of the measurement (c) solvent may play an important role in determination of the observed blend of effects (d) it is the first three conditions which lead to the deterioration of the single substituent parameter treatment as a means of general and relatively precise description of observed electronic substituent effects in the benzene series. 

Table XIV lists comparative SD and /values for fittings of all the sets of Table Xlll with each of the scales of Table V, the FandR values of Swain, and with the single substituent parameter treatment, po y These statistics, coupled with structural considerations, we believe support the usefulness and uniqueness of a scale of limited generality. In general, the / values of Table XIV for the Or scale are smaller than those of the other scales by factors of from 2 to 10. The root-mean-square F values for the other scales are from 2.25 (< j (BA)) to 3 to 4 (S L,, cr (yv)) times that for. Because this analysis has demonstrated that Swain s F and R are generally inferior for the discriminating data for all four types, there appears little to encourage proliferation of these parameters.

Kinoshita, K., Small-particle effects and structural considerations for electrocatalysis, in Modem Aspects of Electrochemistry, 1. O M. Bockris, Eds., Vol. 14, Kluwer, New York, 1982, p. 557. 

Each of the following carbenes has been predicted to have a singlet ground state, either as the result of qualitative structural considerations or theoretical calculations. Indicate what structural features might stabilize the singlet state in each case. 

Traditionally, HTS groups first determined their resource limited capacity for confirmation assays of HTS hits and then used either high potency or chemical structure considerations to pick that number of compounds for retest. The correlation... 

A suitable extrathermodynamic approach is based on structural considerations. The oldest assumption of this type was based on the properties of the rubidium(I) ion, which has a large radius but low deformability. V. A. Pleskov assumed that its solvation energy is the same in all solvents, so that the Galvani potential difference for the rubidium electrode (cf. Eq. 3.1.21) is a constant independent of the solvent. A further assumption was the independence of the standard Galvani potential of the ferricinium-ferrocene redox system (H. Strehlow) or the bis-diphenyl chromium(II)-bis-diphenyl chromium(I) redox system (A. Rusina and G. Gritzner) of the medium. 

There are significant differences in structural considerations between landfills and surface impoundments. First, liners used in surface impoundments have a long-term exposure to the waste and to sunlight. In addition, surface impoundments have a potential for gas in the LCRS because there will always be the potential for organic material beneath the system. 

Lastra AL, Ramirez TO, Salazar L, Martinez M, Trujillo-Ferrara J. The ambrosanolide cumanin inhibits macrophage nitric oxide synthesis some structural considerations. J Ethnopharmacol 2004 95 221-227. 

In Section III, a distinction is made between experimental conformation and folded conformation. Thus, the most populated conformation of a peptide is identified as the folded conformation, irrespective of experimental or secondary-structure considerations. The folded state is then associated to the folded or most populated conformation, while the unfolded state embodies all other conformations and includes any other substates. 

Diol epoxides. Structural considerations. Because enzymatic hydration of arene oxides produces trans dihydrodiols in mammalian cells, there are two diastereomeric series of diol epoxides. In... 

Conformational and electronic structure considerations are the main subjects treated in studies on dithiolanes and related open-chain species123 124 129 of the structures I and n. 

H. N. Russell analyzes solar spectrum with theoretical transition probabilities and eye estimates of line intensities. Notes predominance of hydrogen (also deduced independently by Bengt Stromgren from stellar structure considerations) and otherwise similarity to meteorites rather than Earth s crust. M. Minnaert et al. introduce quantitative measurements of equivalent width, interpreted by the curve of growth developed by M. Minnaert, D. H. Menzel and A. Unsold. 

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