Equivalent diamond-lattice conformations of cyclodecane

Another important feature associated with heterocyclic rings is the reduced van der Waals forces, which can result from replacement of a methylene group in cyclohexane by dicoordinate oxygen, tricoordinate nitrogen, and di- or tricoordinate sulfur. This effect is readily apparent in d5-2-methyl-5-tert-butyl-l,3-dioxane, in which the preferred conformation has the tert-hutyl group axial and the methyl group equatoriar  

3- dithianes, along with their comparative -AG° values in cyclohexane. 

The decreased preference for the equatorial orientation of a 5-alkyl group in 

3- dioxanes and 1,3-dithianes is evident from these data. It is also interesting that the increased preference for the equatorial orientation of a 2- or 4-methyl group in 

3- dioxane disappears in going to 1,3-dithiane. The conformational free energies of 2-alkyl substituents in 1,3-dithianes are very similar to those of cyclohexane (actually slightly smaller) because of the longer C-S bond length compared to C-O. 

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

The relationship of the boat-chair-boat conformation of cyclodecane to the diamond lattice is shown in Fig. 3.7. It is often difficult, even with models, to visualize the shape of medium and large rings. If the molecule does adopt a diamond-lattice conformation, it becomes a much more simple matter to develop a feel for its shape. The two views of the boat-chair-boat conformation, for example, are each used in the literature about equally, and it usually requires considerable scrutiny on the reader s part to verify that they represent the same conformation. By recognizing them as equivalent pathways about a symmetrical diamond-lattice framework, the... 

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