Conformational analysis of ring pucker

Abstract

The conformation of a general puckered ring is defined by a linear combination of normal atomic displacements, according to the irreducible representations of the DNh symmetry group. Each tw.odimensional representation contributes two uniquely defined primitive modes, superimposed on a onedimensional crown form that only exists for N even, adding up to N-3 primitive forms, for any N. The normalized linear coefficients are independent of the amplitude of pucker and of the ring numbering scheme. The formalism applies to any ring type and a quantitative characterization of conformations, intermediate between the conventional classical forms, is possible. It provides the basis for mapping conformations as a function of puckering parameters and a simple algorithm for the identification of the classical forms. The procedure relates general ring conformations to a few simple shapes, familiar to chemists, without losing the advantage of quantitative puckering analysis.

Facial triad modelling using ferrous pyridinyl prolinate complexes: synthesis and catalytic applications

“…The proline ring in both structures has the envelope conformation, for complex 14 (cosform 0.966, sinform 0.034) 28 and for complex 15 (cosform 0.804, sinform 0.196). 27 Selected bond lengths and angles of complexes 14 and 15 are depicted in Table S6.…”

Geometry of the iminium moiety. II. Structures of four cycloalkylidene derivatives of a dihydropyrazolium salt

“…In Table 4(c) the results obtained from program CONFOR (Evans & Boeyens, 1989) 10% from a primitive form X, CONFOR reports the ring as an X form. If the difference is between 10 and 20% the ring is reported to be very similar to an X • form.…”

Dichloro(di-2-pyridylamine)zinc(II): a redetermination at 110 K

“…The central six-membered chelate ring, containing the Zn atom, three N atoms and atoms C5 and C6, is puckered. A conformational analysis (Cremer & Pople, 1975) shows that this ring has an envelope conformation (Evans & Boeyens, 1989), with the Zn atom 0.1436 (3) Å above the plane. A closer inspection of the anisotropic displacement parameters indicates that the amine atom N2 has the largest anisotropicity and moves perpendicular to the plane.…”