CONFOR Conformation analysis

The various conformations of cyclohexane are in rapid equilibrium with one another, but at any moment almost all of the molecules exist in the chair confor mation. Not more than one or two molecules per thousand are present in the skew boat conformation. Thus, the discussion of cyclohexane confor-mational analysis that follows focuses exclusively on the chair confor mation. 

Beginning with cycloheptane, which has four confomnations of similar energy, conformational analysis of cycloalkanes becomes more complicated. The sane fundamental principles apply to medium and large rings as apply to smaller ones—but there ar e more atoms and more bonds to consider and more confor-mational possibilities. 

These remarkable observations stimulated an investigation to understand the origin of the directing effect. To clarify the contribution of the axially- and equato-rially-oriented oxygen atoms in the ketal, a survey of the reaction of three confor-mationally biased t-butyl cyclohexenone ketals 78, 81 and 84 was undertaken (Scheme 3.26) [56]. In each case, careful conformational analysis provides critical clues to rationalizing selectivity. 

In our system, conformational analysis is performed by the module CONFOR. An analysis is defined by specifying the bonds to> rotate, the increment of rotation, and the total number of degrees to rotate. On the basis of this information the program calculates the number of conformations which would result. If the problem is too large to be done interactively (>5 CPU minutes), the problem can be simplified or CONFOR can be used to initiate a background batch job which will perform the analysis. 

The analysis provided for the conversion of 89 to a spiroketal is abbreviated. What other chair conformations are available to 87 and SS. What products would result from cyclization through 88 and/or these additional confor-mations. What would be the expected product if thermodynamics controlled the entire cyclization process. (Calcimycin-10)... 

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