Transannular distance

The eight-membered rings 13.14 normally adopt boat conformations in the solid state with short S=N bond distances (1.51-1.52 A) that are typical of sulfur diimides. There are no transannular S S contacts. The sole exception is the antimony derivative BuSb(NSN)2Sb Bu, which is a planar eight-membered ring. 

Thereby, the presence of tertiary monophosphines is critical, because both polymeric (26) and cyclic tetrameric (24 and 25) complexes can be obtained depending on the phosphine added to the reaction mixture. Furthermore, with some of the phosphines rapid decomposition and deposition of metallic silver occurs. In the macrocyclic molecules 24 and 25 a pair of silver atoms is bridged by two bis(l-imidazolyl)borate moieties, with a transannular Ag Ag distance of 8.61 A for 24 and 8.89 A for 25. The conformations of 24 and 25 are... 

Perfluoro-substituted four- and six-membered (Si-N) ring systems (3, 5) can be obtained by reacting dilithiated silylamines with SiF4. Cyclodisilazanes of the type 3 are the smallest known four-membered (Si-N) rings. Transannular Si Si ring distances of 237 pm are found [1,3]. For the first time cyclotrisilazane crystallizes in twist conformation [1]. 

Also, the Fe methyl contact distance of 3.005(2) A in 34 shortens to 2.085(5) A when the Fe—C-l bond is formed. The most dramatic feature of this rearrangement is that the two acyl carbon donor atoms of 34 have undergone a transannular, interligand C—C coupling reaction. 

Raman spectroscopy is a useful probe for detecting transannular S - S interactions in bicyclic or cage S-N molecules or ions. The strongly Raman active vibrations occur at frequencies in the range 180-300 cm-1, and for S- -S distances in the range 2.4-2.7 A. On the basis of symmetry considerations, the Raman spectrum of the mixed sulfur-selenium nitride S2Se2N4 was assigned to the 1,5- rather than the 1,3- isomer.37... 

The unusually facile formation of a disulfonium dication from sulfide 10 is the result of stereochemical features of the eight-membered ring, which favor the formation of a transannular bond.31 According to X-ray data (see in Chapter 7.1 Table 1), the distance between the two sulfur atoms in 1,5-dithiacyclooctane 10 is smaller than the sum of their van der Waals radii (3.75 A), which results in a strong non-bonded interaction between the atoms confirmed by photoelectron spectroscopy and mass spectrometry.32 33 This interaction and the sulfur-sulfur distance can be decreased as a result of bond formation with an electronegative substituent as in sulfoxide 13 or sulfoximine 14.34,35... 

Structural Analysis. H2[pz(A4)] A = dispiroketal (190) has been structurally characterized, Fig. 40, and is shown to exhibit a noncrystallographic D2 symmetry the central core is planar to within 0.08 A. The presence of hydrogen atoms on the nitrogen centers distorts the potential D4 symmetry of the non-hydrogen atoms The transannular porphyrin N—N distances differ by-0.15 A (11). 

Planar 30a is obtained by dehalogenation of 29a [42], Upon heating, 30a rearranges to the folded 1,3-diborete 28a. Its X-ray structure analysis revealed the shortest transannular C-C distance (174 pm) in l,3-dihydro-l,3-diboretes [43],... 

According to Lonsdale et al., the four aromatic bridgehead atoms C8, Cg, Cu and C14 are bent out of the plane of the remaining benzene carbon atoms by about 0.168 A (14°) at 291 °K (see Fig. 1) the aromatic nuclei are deformed into a boat conformation. The distance between the aromatic bridgehead atoms C3, C14 and Cg, Cu has shrunk to 2.751 A. The intramolecular distance between the plane formed by atoms C4, C5, C7, Cg and that formed by atoms C12, C13, C15, Ci6 is only 3.087 A the van der Waals distance between two parallel benzene nuclei is usually at least 3.4 A. There must therefore be considerable transannular -overlapping in compound 2. To compensate for this the CH2-CH2 bond length is unusually large 1.630 A at 291 °K at 93°K it is only 1.558 A. 

This structiire may be compared with those of the recently reported isoelectronic carbon analogues RC(NSH)2CR(13, R=Me2N,Ph). In the carbon compounds the effect of the exocyclic substituent on ring conformation is remarkable. Thus the phenyl derivative is completely planar and has structural parameters consistent with a 10 TT-electron system while the dimethylamino derivative has a folded structiire with a transannular S-S distance of 2.I38 (Figure 3). 

The alkaloid senkirkine has already been mentioned in Section 5.19.2.1 cf. 37). The eight-membered ring has both an endocyclic double bond and a short 1,5 carbonyl-nitrogen distance, and can best be described as a rather distorted boat-chair (446) with the double bond at the 1,2-position and the transannular interaction at the usual 3- and 7-positions (conformational numbering) cf. 426). A related alkaloid, clivorine, has a very similar structure to senkirkine (72AX(B)2825). 

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