C. Romers

Conformation of non-aromatic ring Compounds—XXV: Geometry and conformation of ring D in some steroids from X-ray structure determinations☆

Abstract A quantitative description of (solid state) steroid ring D puckering and conformation in terms of maximum angle of torsion ϕ m and “phase angle” of pseudoration Δ has considerably improved the approach to the problem of describing flexible 5-membered rings. The maximal torsional parameter ϕ m of all steroid rings D is relatively constant (47°) although a slight tendency to increase with increasing phase angle is noted. The phase angles of 17-keto steroids are negative (= rotation toward C(14) envelope form), those of the otherwise substituted steroids are limited to a rather narrow range comprising about one quarter of the possible circuit. A C(13) envelope has not been found thus far. Some empirical rules that may serve as a basis for the discussion of ring D conformation can now be recognized. In first approximation the nature of the C(17) or C(16) β substituent (except keto) has no discernible influence. Extreme deformations of rings A, B and/or C do affect ring D. The effect of the angular methyl groups C(18) and C(19) cannot yet be assessed for lack of information on nor-steroids. X-ray studies on a diversity of well chosen compounds will be necessary to elucidate the role of each conformation-determining factor. Solution data (NMR, infrared, ORD, CD, and dipole moments), interpreted in accordance with the now established “conformation laws” of ring D, may be of considerable help in this respect.

Conformation of non-aromatic ring compounds—XXIV : On the geometry of the perhydrophenanthrene skeleton in some steroids

Abstract A quantitative description of the conformation of the A,B,C,-moiety of eight steroids in terms of valency and torsional angles is given. The geometrical details of the molecules from X-ray structure determinations are compared with those obtained from theoretical considerations on appropriately substituted cyclohexane and cyclohexene rings. It is shown that the use of such building material leads to a qualitative agreement. A number of interactions present in a steroid, but not in a cyclohexane unit, prevents a quantitative agreement. The steroid skeleton (all trans ) has a somewhat bent overall shape. The occurrence of conformational transmission effects is discussed and a number of rules concerning the torsional angles around junctions given.

Conformation of non-aromatic ring compounds—LI : The crystal structure of trans-1,4-dichlorocyclooctane at −180°

Abstract Crystals of trans -1,4-dichloro-cyclooctane are monoclinic with space group P 2 1 /c and Z = 4. The unit cell dimensions at −180° are a = 14·10, b = 5·53, c = 12.18A and β = 113·1°. The structure was solved by calculation of a minimum function M 4 and refined by the least-squares method. The ring has the boat-chair conformation, its symmetry being approximately C s . The one chlorine atom at the top of the chair moiety points to the axial direction, the other one to a (pseudo-) equatorial direction. The mean ring valency angle is 116·4°. Due to steric interaction the carbon chlorine bonds are large, their mean value being 1·83A.

The crystal structure of 8,8'‐dibromo‐2,2'‐methylenediquinoline

The structure has been refined by the least-squares method. The final R value is 13.1% and the standard deviations are of the order of 0.001 A for the bromine atoms and 0.008 ~ and 0-01/1, for the nitrogen and carbon atoms respectively. The molecular system is non-conjugated: the central carbon atom is clearly a CH2 group connected with C-C bonds of 1.51 A to the quinoline rings. The C-CH2-C valency angle is 111.5 ° and the dihedral angle between the two planar quinoline rings is 77 °. The observed red colour of the crystals is not in agreement with the firmly established non-planar conformation. It is assumed that the structure is an example of an anomalous mixed crystal in such a way that a small proportion of planar molecules, viz. the tautomer BrNHC9Hs:CH. C9HsNBr, is present in the lattice.