1. Steric strain in a large molecule is often reduced by changes in torsion angles. However, in smaller sets of fused be

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1 Steric Strain In A Large Molecule Is Often Reduced By Changes In Torsion Angles However In Smaller Sets Of Fused Be 1 (31 KiB) Viewed 35 times

1. Steric strain in a large molecule is often reduced by changes in torsion angles. However, in smaller sets of fused benzene rings, like phenanthrene and 3,4-benzophenanthrene (shown below), the first geometric parameters to vary from reference values are found to be the central bond lengths and bond angles. Why do they expand to relieve steric strain before the molecule undergoes torsion to a non-planar structure? Phenanthrene 3,4-Benzophenanthrene