Interconversion of Carbon Sites in Boat-Chair-Boat Cyclodecane; Conformations of Chlorocyclodecane and Cyclodecyl Acetate

Abstract

Interconversion of carbon sites in boat-chair-boat (BCB) cyclodecane occurs by way of the twist-boat-chair (TBC) conformation, which predicts that C-1 exchanges with C-4, etc. The previously obtained low-temperature 13C spectra could be matched by assuming (1,4) or (1,3) exchange, but not (1,2) exchange. A free-energy barrier of 5.54 kcal/mol was obtained for conversion of BCB to TBC at -137.4 degrees C. The major conformation of chlorocyclodecane and cyclodecyl acetate is assigned to the IIIe BCB.

Cyclodecyl 4-nitrophenylacetate

“…Kolossvary & Guida (1993) carried out a comprehensive study of conformational equilibration for 2with Allinger's MM2 program and concluded that (2a) equilibrates only with (2c) within a 12 kcal mol À1 window. Wiberg (2003) calculated a free-energy barrier of 5.4 kcal mol À1 for the BCB to TBC conversion at room temperature, in good agreement with a later experimental determination of this barrier (5.54 kcal mol À1 at 136 K; Pawar et al, 2006).…”

“…The low-temperature 13 C spectrum of the substituted ring carbon of chlorocyclodecane, (3), in solution showed three peaks at 67.67, 66.14 and 61.63 [(3a), (3b) and (3c), respectively], with populations of 31.2, 14.9 and 53.9% (Pawar et al, 1998). These peaks were assigned to IIe BCB, IIa BCB and a TBCC conformation, respectively, but the assignment for the major conformation, (3c), was later changed to IIIe BCB (Pawar et al, 2006). The low-temperature 13 C spectra for cyclodecyl acetate, (4), in solution show three peaks for the substituted ring C atoms, with relative positions and intensities similar to those of (3), which suggested that the populated ring conformations are the same for (3) and (4) (Pawar et al, 1998).…”

Congested molecules. Where is the steric repulsion? An analysis of the electron density by the method of interacting quantum atoms

“…Similar calculations were also performed on cyclodecane ( 10 ). The structure of this molecule has been studied experimentally by X‐ray crystallography, gas phase electron diffraction, and NMR spectroscopy . The various conformations have been reviewed recently .…”

“…Results indicate that, in all molecular models studied, a bond path is found to exist between the congested atoms. At equilibrium, that is, for the energy minimized molecular structures, the congested atoms are found to be separated by a distance well below the sum of the van der Waals radii, an observation also confirmed by a number of available experimental structures of some of the molecules shown in Scheme and similar compounds found in the literature …”

Asararenes—A Family of Large Aromatic Macrocycles

“…The backbones ( Figure 4 d and e) of asar[9]-and asar [10]arene adopt conformations similar to those available to cyclononane and cyclodecane, respectively, while the shape of asar [10]arene is best described as a twisted chair-boat-chair (CBC) conformation. [38] Finally, the backbone (Figure 4 f) of asar [11]arene is folded up into a "taco" shape with two "grooves"-potential binding-sites for flat or rod-shaped guests.…”