Bond distance derivatives

Although gas-phase structures of polyatomic molecules which are derived by ED or MW cannot be compared strictly with each other, differences between ra and rz or between ra or r0 lie in general within the combined experimental uncertainties of both methods. The comparison between bond distances derived in the gas phase and those obtained by X-ray crystallography, however, is much more difficult, if not impossible. Three different effects may cause systematic differences ... 

Table 8.5 Bond distances derived by PDF curves from MD (A, error within 0.05)... 

High level molecular orbital calculations of cyclobutadiene itself and experimen tally measured bond distances of a stable highly substituted derivative both reveal a pat tern of alternating short and long bonds characteristic of a rectangular rather than square geometry... 

Structural parameters and interatomic distances derived from electron diffraction (7) (77JST(42)l2i) and X-ray diffraction (8) studies (76AX(B)3178) provide unequivocal evidence that pyrazine is planar with >2a symmetry. There is an increased localization of electron density in the carbon-nitrogen bonds, with carbon-carbon bonds being similar in length to those in benzene. ... 

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. 

X-ray crystallographic analyses of the structures show that the P-S bond distance vary over one-half of an Angstrom (2.36-2.88 A). The derivatives were generated using procedures similar to those utilized to form pentaoxyphosphoranes with P-N bonds, that is (i) the oxidation of sulfur containing cyclic chlorophosphines with a quinone or (ii) treatment of phosphites with the sulfur-containing diol in presence of N-chlorodiisopropylamine. Two typical examples of these synthetic protocols are shown in Scheme 10. 

The crystal of 2 OPr recrystallized from EtOH/H20 solution, and the mixed crystal of the same ethyl and propyl cinnamate derivatives (2 OEt and 2 OPr), on photoirradiation for 2h at room temperature with a 500 W super-high-pressure Hg lamp, afforded the highly strained tricyclic [2.2] paracyclophane (2 OEt-2 OPr-cyclo) crystal quantitatively (Maekawa et ai, 1991b). A crystal structure analysis was carried out of a single crystal of the complex of 2 OEt-2 OPr-cyclo with HFIP (recrystallization solvent) in a 1 2 molar ratio. Fig. 13 shows the molecular structure of 2 OEt-2 OPr-cyclo viewed along the phenylene planes. The short non-bonded distances and deformation of the benzene rings, as seen in Fig. 13, are common to those of [2.2] paracyclophanes, as previously reported (Hope et ai, 1972a,b). 

Often one of the diatomic bond distances r or r2 can be used as s. Insertion of Eq. (41) into Eq. (40), coupled with arguments such as those in Section IIC to connect < >/( ) to RWP iterates, then leads to an expression for Eq. (40) within the RWP framework [13]. The relevant reaction probability expression, Eq. (18) of Ref. [13], which need not be detailed here, involves Fourier transformation of ls=so ( ) / ls=so ( ) requires the real wave packet and its derivative... 

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