Structural Investigation

The first structural investigations on cydic tetraynes were carried out in 1957 by Sondheimer [23b]. These studies revealed for 2(3) the presence of a center of symmetry that implies a chair conformation in the soUd state, as is known for cyclohexane and 1,6-cyclodecadiyne. Later, more accurate results on the solid state geometry of 2(3) and 2(4) were obtained [72]. In contrast to 2(3), the larger homologue 2(4) adopts a twisted conformation. Structural data has also been obtained for the even more strained cyclotetraynes 17,19 and 77b (R = TIPS) that are tethered by only two saturated carbon atoms [37, 65]. In Fig. 7.1 a comparison between the X-ray structures of 2(3) and 17 showing the top and a side view is displayed. The most relevant parameters and their definition for 2(3), 2(4) and 17 are given in 

Structural investigations were also carried out on the nitrogen-containing analogs 10(n) and 27b-e [32, 33, 39]. The X-ray structures of the cyclotetraynes 27b-e with two nitrogen atoms in each tether reveal a crystallographic center of inversion. Thus, all molecules adopt a chair conformation in the solid state like the all- 

This unexpected behavior was also observed in the case of various 1,6-disubsti-tuted diazacydodeca-3,8-diynes [73]. The axial orientation of the substituents at the nitrogen atom(s) in 10 or 27 cause a gauche arrangement between the lone pair at the nitrogen atom and the CH2 groups. This implies an anti arrangement with the o(CC) bond (Fig. 7.3, left). 

Whereas the above presented examples such as 49 and 50 show a compact structure with a cavity inside, large monocyclic systems such as tetrachalcogenacyclote-traynes and hexachalcogenacyclohexaynes 29(n) and 33(n)-35(n) [40] adopt a more open structure with a large free accessible space. This opens up the possibility of supramolecular organization. 

In contrast to cyclic tetrachalcogenadiynes [75], the conformations of cydic tetra-chalcogenatetraynes [76] are not mainly determined by electronic effects. In the smaller counterparts (cydic tetrathia- and tetraselenadiynes) where only one triple bond links the chalcogen centers the repulsive interaction between the lone pairs of the chalcogens is the structure-determining interaction [75, 76]. This repulsive interaction is remarkably reduced by the longer distance spanned by the two acetylene units. The favored perpendicular conformation is circumvented by steric or 

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Structural investigations of metal-ion hydration have been carried out by spectroscopic, scadering and diffraction teclmiques, but these teclmiques do not always give identical results since they measure in different timescales. There are tliree distinct types of measurement ... 

Schertel A, Hahner G, Grunze M and Well C 1996 Near edge x-ray adsorption fine structure investigation of the... 

Kolb D M 1988 Structural investigations of electrode surfaces Ber. Bunsenges. Phys. Chem. 92 1175-87... 

Structural investigations of heavy metal oxides (particularly when oxygen positions or occupancies are important)... 

The SFM images shown in Fig. 11 have proved that CNTs are promising for nanoscale structural investigation and are better than the normal silicon nitride probes [36]. 

The most general method for synthesis of cyclic enamines is the oxidation of tertiary amines with mercuric acetate, which has been investigated primarily by Leonard 111-116) and applied in numerous examples of structural investigation and in syntheses of alkaloids 102,117-121). The requirement of a tram-coplanar arrangement of an a proton and mercury complexed on nitrogen, in the optimum transition state, confers valuable selectivity to the reaction. It may thus be used as a kinetic probe for stereochemistry as well as for the formation of specific enamine isomers. 

J. Jander, Recent chemistry and structure investigation of NI3, NBr3, NCI3 and related compounds, Adv. Inorg. Chem. Radiochem. 19, 1-63 (1976). 

In the course of structural investigations of a number of jS-carboline alkaloids, reactions leading to ring cleavage have been encountered. Oxidation of harmine (271) and of harmaline... 

T. G. Takhirov X-Ray Structural Investigation of Stereochemi-cally Nonrigid Tetracoordinated Metal-Chelates of Zn(II), Cd(II), Hg(II) and Ni(II) on the Base of Derivatives of 4-... 

Mass spectrometry in structural investigation of diterpene alkaloids 97IZV1096. 

Synthesis, transformations, and structural investigation of derivatives of dehydroamino acids containing heterocyclic ring as a substituent 97CLY-610. 

The information obtained from X-ray measurements on the arrangement of the water molecules naturally depends very much on the resolution and state of refinement of the crystal structure investigated. For detailed information on the organization of water molecules in the protein hydration shell at the surface and on the bulk water in the crystals a 1,2 to 1,8 A resolution range is necessary 153>. 

By diluting HF by means of multiple additions of water, followed by the evaporation of a solution initially prepared by the dissolution of NaF and Nb205 in HF, Stomberg [58] obtained Na3NbOF6 in the form of small single crystals that were suitable for X-ray structure investigations. 

The betaines 3 have been claimed to give the trithiepine 4 on standing,330b but an X-ray structural investigation showed the product to be a 3,5-bis(alkylidene)-l,2,4-trithiolanc.330a... 

The chemistry of silicon in very low oxidation states is one of the most fascinating research areas, which can be located between molecular compounds of silicon and elemental (perhaps amorphous) silicon [190-194]. Most interesting results have recently been obtained by structural investigations of siliddes in Zintl phases. However, compounds of silicon with negative oxidation states and very low coordination numbers of 1, 2, and 3 are so far only known in the composite of a crystal lattice. 

Mass Spectra and Chemical Structure While there are a number of books (Refs 16, 30, 49 64) already referred to, which deal with details of the instrumentation and techniques of mass spectrometry, there are several concise introductory texts (Refs 10, 21 52) on the interpretation of mass spectra. Still other recent books deal comprehensively with organic structural investigation by mass spectrometry. One of these (Ref 63) discusses fundamentals of ion fragmentation mechanisms, while the others (Refs 7, 15, 20, 28 29) describe mass spectra of various classes of organic compounds. In the alloted space for this article methods of interpretation of mass spectra and structural identification can not be described in depth. An attempt is, therefore, made only to briefly outline the procedures used in this interpretation... 

The first crystal structure investigation was reported by Romming (1959, 1963) for benzenediazonium chloride. An unpublished low temperature study ( —160 °C) by Romming is mentioned by Sorriso (1978). Romming and Tjornhom (1968) investigated the structure in the presence of one equivalent of CH3COOH. More... 

The structural investigations have been extended to potassium derivatives of the "super" formamidine HC(NC6H3Pr2-2,6)(NHC6H3Pr2-2,6) ( = HDippForm). Treatment of the free formamidine with KN(SiMe3)2 yielded the formamidinate species [K(DippForm)2K(THF)2l (THF) , which exhibits a macromolecular structure of alternating fj -arene f/ -amidinate bound potassium di-amidinate and potassium di-THF units in a one-dimensional polymeric array (Figure 5). Addition of a further equivalent of HDippForm afforded hydrogen-bonded [K(DippForm)(THF)3](HDippForm). ... 

Recent Chemistry and Structure Investigation of Nitrogen Triiodide, Tribromide, Trichloride, and Related Compounds... 

The phase diagram for the Sr-Au system shows three congruently melting phases, /3-SrAu (970°C), SrAu2 (1085°C) and SrAu, (1040°C) four phases formed in peritectic reactions are also observed, Sr Au (640°C), SrjAu (590°C), y-Srj Au (750°C) and 5-Sr,Au2, which has a limited stability range from the eutectoid (725°C) to the peritectic reaction (770°C). Independent structural investigations confirm the forma-... 

Djabourov M., Leblond J., Papon P. Gelation of aqueos gelatin solutions. I. Structural investigation. J. Phys. France 49 (1988a) 319-332. 

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