Cyclodecane conformations

Fig. 9. Energetically favourable cyclodecane conformations with calculated angles (deg inner values) and torsion angles (53) (force field of Ermer and Lifson (19)). The conformations are further characterised by (from top) conformational symbol (11), symmetry, calculated relative potential energy (AV) and relative enthalpy (AH kcal mole-1 T = 298 K reference BCB AH = AV + AHvibr, see Section 3.3.). For BCB experimental angles and torsion angles (46) are also given (in parentheses)...

A full structure has been reported for the centrosymmetric hydrated 1,6-diphosphacyclodecane derivative (25), in which the ten-membered ring has the normal cyclodecane conformation. The phenyl groups are in trans-pseudo-axial positions and the structure is completed by hydrogen bonds between the hydrate water and phosphoryl groups from two molecules. 

Studies of cyclodecane derivatives by X-ray crystallographic methods have demonstrated that the boat-chair-boat conformation is adopted in the solid state. (Notice that boat is used here in a different sense than for cyclohexane.) As was indicated in Table 3.7 (p. 146), cyclodecane is significantly more strained than cyclohexane. Examination of the boat-chair-boat conformation reveals that the source of most of this strain is the close van der Waals contacts between two sets of three hydrogens on either side of the molecule. 

Fig. 3.7. Equivalent diamond-lattice conformations of cyClodecane (boat-chair-boat).

Examine the structure of cyclodecane, a molecule which contains the same number of carbons as decalin, but only has one ring (a model of the most stable conformation is provided). Compare it to cis and trans decalin. Make a plastic model of cyclodecane. Is it flexible or locked What conformational properties of cyclodecane can be anticipated from the properties of decalins What properties cannot be anticipated How do you account for this ... 

Cyclobutanc, angle strain in. 115-116 conformation of. 115-116 molecular model of, 116 photochemical synthesis of, 1190 strain energy of, 114 torsional strain in, 115-116 Cyclodecane, strain energy of. 114 Cyclodecapentaene, molecular model of, 525, 540... 

Fig. 3. Symmetry elements and torsion angles of cyclohexane (chair conformation) and cyclodecane (stable BCB-conformation)...

In a similar way the potential constant method as described here allows the simultaneous vibrational analysis of systems which differ in other strain factors. Furthermore, conformations and enthalpies (and other properties see Section 6.5. for examples) may be calculated with the same force field. For instance, vibrational, conformational, and energetic properties of cyclopentane, cyclohexane and cyclodecane can be analysed simultaneously with a single common force field, despite the fact that these cycloalkanes involve different distributions of angle and torsional strain, and of nonbonded interactions 8, 17). This is not possible by means of conventional vibrational spectroscopic calculations. 

The problem of the preferred conformation of cyclodecane has been extensively studied by Dunitz et al. (46). In the crystals of seven simple cyclodecane derivatives (mono- or 1,6-disubstituted cyclodecanes) the same conformation was found for the ten-membered ring (BCB-conformation, Fig. 9). It follows from this that the BCB-conformation is an energetically favourable conformation, possibly the most favourable one. Numerous force field calculations support this interpretation Of all calculated conformations BOB corresponded to the lowest potential energy minimum. Lately this picture has become more complicated, however. A recent force field calculation of Schleyer etal. (21) yielded for a conformation termed TCCC a potential energy lower by 0.6 kcal mole-1 than for BCB. (Fig. 9 T stands for twisted TCCC is a C2h-symmetric crown-conformation which can be derived from rrans-decalin by breaking the central CC-bond and keeping the symmetry.) A force field of... 

The most stable conformation of cyclodecane has a C-C-C bond angles of 117°. 

When we study the case of cyclodecane, we find that x-ray crystallographic studies reveal that the most stable conformation has C—C bond angles of 117° which indicates some angle strain from the normal 109°28. So the wide bond angles allow the molecule to expand and minimise unfavourable repulsions between hydrogens across the ring. 

X-ray analysis has shown that cyclodecane in its most preferred conformation exists as shown below in which the two chain forms of cyclohexane are joined by 1,3 axial bonds and six hydrogen atoms are intraannular and 14 peripheral. 

The systematic conformational search for herbarumin I (40) using the MMX force field as implemented in the PCMODEL program revealed the presence of the minimum energy conformation depicted in Fig. 11 (Tmmx = 9.51 kcal/mol), which is related to the chair-chair-chair conformation found in cyclodecane.In this conformation, the value of... 

Figure 12-18 Most stable conformation of cyclodecane Dale and sawhorse representations. The shaded area in the sawhorse convention indicates substantial nonbonded H - - H interactions.

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

Rings larger than six-membered are always puckered unless they contain a large number of sp atoms (see the section on strain in medium rings, p. 223). The energy and conformations of the alkane series cycloheptane to cyclodecane... 

Of course, favourable conformations in the educts are required for the success of these reactions. The same is valid for the [1,2,6]- or [l,2,7]-eliminations of the cyclodecanes 167 (proof of H-migrations by 2H- and 14C-labeling experiments)95) and 170 96) (171 forms without loss of deuterium). 

Ahyd// was measured in acetic acid solution. No experimental uncertainty was given. The unexpectedly large Ahy(,//of l,l,4,4-tetramethylcyclodec-7(8)-ene, (Z), which causes the usual E, Z stability relationship in cycloalkenes to be reversed, is brought about by strain. The conformation of the cyclodecane ring of 1,1,4,4-tetramethylcyclodec-7(8)-ene, (Z) forces a methyl group into the energetically... 

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