Experimental charge density study of 7-dispiro[2.0.2.1]heptane carboxylic acid

Abstract

The experimental charge density distribution in 7-dispiro[2.0.2.1]heptane carboxylic acid has been determined using single-crystal X-ray diffraction data measured at 100 K. Multipole refinement converged at R-0.023 for 5539 reflections with I > 30-(/) and sin 0/A < 1.08 ]k -1 . Inclusion of hexadecapole functions for C atoms in the refinement is shown to be necessary. Experimental maps of the deformation density and of the Laplacian of p are in good agreement with those from ab initio calculations and also have some features specific for polyspirocyclopropanes. Analysis of the bond critical-point properties reveals that the effect of the 7r-acceptor hydroxycarbonyl substituent is more pronounced on the endo-side of the molecule, which can be related to the chemical behaviour of the compound. The influence of small conformational changes on the bond length distribution in the skeleton is also discussed.

Novel Synthesis and Structures of Tris-Annelated Benzene Donors for the Electron-Density Elucidation of the Classical Mills−Nixon Effect

“…The latter results in a decreased bond length ( d ) and increased bond bulge (δ), which are quantitatively evaluated in Table , columns 2 and 4, respectively. Such a shortening of d and bulging of δ in the exo bond corresponds to a “banana” bond distortion of the type previously described by Boese and others , column 5).…”

“…(b) Such a change of π-character accompanying annelation differs from Boese's intepretation,28a since the increase in the bond bulge δ for the exo bonds relative to the endo bulge is not accompanied by a significant decrease in the corresponding bond length relative to the bond path, as shown by the comparison of ( d ) and ( p ) in Table .…”

“…To quantify the difference in these electron-density distributions, we employ the ellipticity ε as the ratio of the orthogonal components (λ x and λ z ) of the gradient, i.e., ε = λ x /λ z − 1, the critical-point values of which are tabulated in Table , column 7 . By taking the ellipticity of a pure σ bond as ε σ = 0 and the π-bond in benzene as ε π ≃ 0.2,28b we interpret the larger value of ε exo in Table as an indication of its greater π-character relative to that of ε endo 30b…”

Bonding in phosphorus ylides: topological analysis of experimental charge density distribution in triphenylphosphonium benzylide †

“…Further analysis of the positions of the BCP can provide useful information about the fine electronic structure of the molecule. 15 The positions of BCP's in the P-C(1)-C(2) system of molecule 1 are rather unusual. In the case of different atomic charges of the covalently bonded atoms one can expect to observe the shift of the BCP towards the more positive atom, which reflects the accumulation of electron density in the atomic basin of the more negative atom.…”

Experimental Determination of the Electron Density Topology in a Non-centrosymmetric Transition Metal Complex: [Ni(H3L)][NO3][PF6] [H3L =N,N‘,N‘‘-Tris(2-hydroxy-3-methylbutyl)-1,4,7-triazacyclononane]

“…For organic molecules containing only first-row atoms, many fine multipole studies have been published using the standard multipole model . In our particular case, the standard scattering formalism including expansion to hexadecapolar functions on P and Ni produced a good fit to the data in terms of agreement indices and a reasonable residual map, but resulted in an unconverged κ‘‘ refinement for the ligating N and O atoms which thus became extremely diffuse.…”