Chain model, constant valence angle

In the segment model, any given angle can occur between neighboring segments. Valence angles, however, must be considered with real chains and, to a first approximation (see Section 4.5.1), they can be taken as constant. As with the segment model [see Equation (A4-2)], all vectors for the A chain units (that is, — 1 bonds) must be multiplied by each other ... 

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