b. Torsion angles

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b. Torsion angles

The torsion angle (or angle of twist) about the bond B--C in a series of bonded atoms A--B--C--D is defined as the angle of rotation needed to make the projection of the line B--A coincide with the projection of the line C--D, when viewed along the B--C direction. The positive sense is clockwise.

$\begin{figure} \includegraphics {figa.ps} \end{figure}$

In general a chain of --CH₂-- groups will have a staggered conformation so that torsion angles are 180 $^{\circ}$ for C--C--C--C and 60 $^{\circ}$ for C--C--C--H or H--C--C--H.

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