Conformations cyclononane

Asii . The nine-membered ring formed has a cyclononane conformation six of the nine ring members are coordinated, three each, to two Mo(CO)3 groups. The same overall structure is maintained when Mn2(CO)io or Re2(CO)io replaces Mo(CO)g, but owing to the increase by one in electron count for Mn or Re compared to Mo, one of the RAs units in the ring looses an organic group to convert it from a two-electron to a one-electron donor ... 

Cycloheptane, cyclooctane, and cyclononane and other higher cycloalkanes exist in nonplanar conformations. 

The conformations of cyclononane are combinations of chair and twist-boat forms as follows ... 

Cyclononane prefers a twist boat-chair (TBC) conformation (see references cited in [110]), with two classes of CH2 groups differing in symmetry ( and ). At room temperature, a rapid inversion between two enantiomeric TBC forms probably occurs, involving an intermediate boat-chair form An averaged spectrum having one signal as in Fig. 3.10(e) is observed (Fig. 3.12) [110]. At very low temperature, this inversion is frozen,... 

Figure 12-17 Twist boat-chair conformation of cyclononane (after Dale)...

Several more or less reasonable conformations of cyclononane also can be developed, but the most favorable one is called the twist-boat-chair, which has three-fold symmetry (Figure 12-17). The activation energy for inversion of the ring is about 6 kcal mole-1. 

Comparison of the heats of combustion of cycloalkanes (Table 9.1) shows that cyclopropane, cyclobutane, and cyclononane yield more energy per methylene group than the other cycloalkanes. This can be attributed to strain resulting from bond-angle distortion (Baeyer strain), eclipsed conformations (Pitzer strain), and trans-annular, repulsive van der Waals interactions. Common (five- and six-membered) rings and large (more than twelve-membered) rings have little or no strain. This... 

The racemic mixture of 36 crystallized as a racemic compound in an achiral space group crystal. Analysis of its X-ray crystallographically determined structure shows one of the enantiomers to have a reference,S)-TCBtype33 conformation as depicted in the iconic drawing for 36 (see Fig. 19). Conformational families exist for cis-3 or trans-44 cyclononenes. The various members of a family maintain similar torsion angles for six of the nine bonds compared to those measured for their cyclononane saturated parent.3 Double bonds are formed from either synclinal or antiperiplanar-type bonds in the parent. Conversion of a single bond to a double bond will usually... 

Disubstituted Cyclohexanes Conformational Energies of Substitutents Conformation and Chemical Reactivity Six Membered Heterocyclic Rings Cyclooctane and Cyclononane Cyclodecane... 

As shown in Figure 4, most of the compounds adopt the conformation shown schematically by 16 (0° and 180°). There are only few compounds that adopt the conformation shown in 17 (180° and 180°) and 18 (0° and 90°). The conformation presented by 16 is dominant, due to the ability to form intramolecular hydrogen bonds. All three conformations are observed in the crystal structure of 10,15-dihydro-2,3,7,8,12,13-hexahydroxy-57f-tribenzo(a,d,g)cyclononane dipropanolate clathrate (19)". 

Another striking contrast has been found in cyclononane and its 1,4,7-trithia derivative (29) whereas the former s most stable conformer has D3 symmetry (55), the most stable conformation of the latter displays C3 symmetry (56). A D3 conformation has been assigned to trimeric acetone peroxide (30) by X-ray crystallography (57). 

D. M. Ferguson, W. A. Glauser, and D. J. Raber,/. Comput. Chem., 10(7), 903 (1989). Molecular Mechanics Conformational Analysis of Cyclononane Using the RIPS Method and Comparison with Quantum-Mechanical Calculations. 

It was found that the boat-chair conformation is in equilibrium with a small amount of a crown form . Only by high-field NMR was it possible to investigate the low-temperature conformations of the medium-sized cycloalkanes such as cyclononane S cyclodecanecyclododecane, cyclotetradecane and cyclo-hexadecane. ... 

Cycloheptane, cyclooctane, and cyclononane and other higher cycloalkanes also exist in nonplanar conformations. The small instabilities of these higher cycloalkanes appear to be caused primarily by torsional strain and repulsive dispersion forces between hydrogen atoms across rings, called transannular strain. The nonplanar conformations of these rings, however, are essentially free of angle strain. 

The conformation state of cyclononane is a crown with a symmetry number of 1 but it is insirfficiently studied and for this reason we have combined the calculations by the Alinjer method with the X-ray data for cyclononylamine bromohydrate [80]. The conformation of cyclododecy-lamine-1,6 dihydrohydrate, which has only one axis of symmetry of second order, is taken as a base for cyclodecane. According to the X-ray data cyclododecane has a square shape conformation with butane segments as... 

If cyclononane exists in the crown structure shown, then the transannular strain indicated is expected to be present and help destabilize the structure. It is also possible that the molecule can partially alleviate some strain by pseudorotation into a different conformation. 

Nine- and Ten-membered Rings.—Conformational energies and interconversion barriers have been calculated for cyclononane. The [3,3,3]-conformation was found to be the most stable. N.m.r. indicated that cyclonona-l,2,6-triene adopts the unsymmetrical twist-boat-chair conformation (19) and undergoes a hindered pseudorotation with an activation energy of 12.9 kcal mol to achieve C2 time-averaged symmetry. ... 

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