Conformational bonds

No Compound Ring Conformation Bond distances Bond angles Ref. 

An enormous number of different 1,3-dioxane structures have been reported since 1996 in Figure 3, mono-, bicyclic and spiro variants are presented, while Figure 4 contains examples of tricyclic structures with the 1,3-dioxane moiety. The conformations, bond lengths, bond and dihedral angles of the 1,3-dioxane rings are determined by the ring fusion, the attached substituents, and the presence of exocyclic double bonds. Thus, published structures are classified as either monocyclic (mono), spiro-substituted (spiro), bicyclic (bi), or tricyclic (tri). The well-known Meldrum s acid derivatives (M) have been most intensively studied. 

Calculated conformations, bond lengths, and bond angles which reproduce correctly the experimental values have shown that compound 7 is planar while molecules 8 and 9 show different degrees of nonplanarity (Table 1) <1997JST(413)1>. 

Cyclohexane as a planar molecule Most stable chair conformation Bond angle 120 of cyclohexane... 

The two main conformational shapes for cyclohexane are called the chair and the boat (Fig.M). The chair form is more stable than the boat form since the latter has eclipsed C-C and C-H bonds. This can be observed in the Newman projections (Fig.N) that have been drawn in such a way that we are looking along two bonds at the same time-bonds 2-3 and 6-5. In the chair conformation, there are no eclipsed C-C bonds. But, in the boat conformation, bond 1-2 is eclipse with bond 3-4, and bond 1-6 is eclipsed with bond 5-4. This indicates that the boat conformation is less stable than the chair conformation and the majority of... 

MM2 Structural Data for BBL Lowest Energy Conformers (bond lengths are in A and distortion parameters are in °I ... 

A variety of other molecular properties can be found, including details of the spatial distribution of segments, the probability of gauche-conformations, bond order parameters (which display alternations between odd and even chain elements, counted from the head group) and tilt behaviour 1). 

Force field calculations have been carried out for compounds CI3PNPOCI2 and CI3PNPCI2NPOCI2. Conformations, bonding and flexibility have been discussed. In order to get some insight in chain flexibility of phosphazene polymers, ab initio MO calculations have been applied to study conformation, chain flexibility, and charge density of valence electrons in the linear trimer Me(NPCl2)3Me.2... 

Considerable progress has been made in the development of theories that can predict the complete ROA spectrum, provided that a good normal coordinate analysis is available, and this leads us to the hope that it might be possible eventually to deduce the total stereochemistry (absolute configuration, conformation, bond lengths and angles) of a chiral molecule in a chemically relevant environment from the measured ROA spectrum (or indeed from the infrared CD spectrum). 

Figure 1.62 Newman projections of to show the dihedral angles subtended about the 0 —P and P—0 bonds (C and a respectively) in order to demonstrate how highly regular dihedral angles set up a highly extended phosphodiester backbone conformation. Bonds are colour coded in the same way as Figs. 1.60 1.61.

S.No Compound Ring conformation Bond distance (A) P Nendo P-Xexo Bond angles ( ) NPN PNP ... 

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