Structure of stenanzidinine
On the basis of the results of a study of the chemical and physical characteristics of the alkaloid itself and of the products of its transformation, the most probable structure and partial configuration of stenanzidinine have been established as 3β, 6α-dihydroxycevanine.
Configuration and reactivity of ten-membered 5,10-seco-compounds obtained by fragmentation of 5-hydroxy-steroids
Abstract Assignment of configuration to the 1,10-double bond in the cis-trans isomeric 3β-acetoxy-5,10-seco-1,10-cholesten-5-ones has been achieved by means of NMR spectrometry. Some reactions of these new compounds have been studied and, as expected from conformational analysis, it was found that only the trans-isomer readily undergoes transannular cyclizations.
Conformation and reactivity of medium-sized ring compounds
Conformational analysis consists in the determination of the energy ( or of the enthalpy) of a conformation by the application of certain rules based upon theoretical considerations and confirmed by experience. Since in general the determination of the absolute energy of a given conformation is not possible, such analysis is limited to comparisons of energy contents of various conformations of one chemical species (molecules, ions, radicals, transition states) or of the conformations of closely related species. The most convenient parameters for the definition of the spatial arrangement ofthe atoms in a particle are bond distances (d), bond angles (ti) and torsion angles (T), because they are independent of the coordinate system. A large body of experimental evidence shows that in stable particles ( consequently not in transition states) the bond distances do not change appreciably upon modification ofthe conformation. For the purpose of conformational analysis one can, therefore, assume them tobe constant and consider only the energy variations due to changes in the bond angles and in the torsion angles. The increase in energy content which arises from a deviation of the actual values of the parameters from their most favourable values is usually called strain (S). The energy increase directly brought about by a deviation of the bond angles from their optimum (e.g. tetrahedral) angle, is known as classical or Baeyer strain (SB)· The one which is directly due to a deviation of the torsion angles is often termed Pi tzer strain ( Sp). A third and very important component of the strain proceeds from the repulsive interactions between non-bonded atoms (SN). These non-bonded interactions are determined by the same parameters d, {} and T, on which the other two types ofstrain mentioned above also depend. However, the expression which defines this dependence in the case of non-bonded interactions between atoms which are separated from one another by several bonds is so complex, that it is more convenient to represent the strain SN as a function ofthe interatomic distances r. Although the total strain can in principle be calculated on the basis ofthe three component strains which have been described above (Figure 1), quantitative conformational analysis is still quite unsatisfactory. For large molecules the deduction of strain from the variables {} and T requires extensive calculations. Such is already the case for the mediumsized cycloalkanes : in cyclodecane, for instance, there occur 405 nonbonded interactions. This difficulty can, of course, be overcome with the help of electronic computers. The most serious trouble is that the functions j 1, j 2, j 3 , f 4 etc. which connect the energy with the variables {} and T are only imperfectly known. Consequently, the considerable computing effort