Flexible to Conformationally Rigid Molecule

The aforesaid critical and important aspect may be expatiated with the aid of the following example of DOPAMINE, which enhances cardiac output by stimulating P-receptors. 

In reality, dopamine (I) may exist in an infinite number of conformation about the single side-chain C—C bond. However, two such conformations, namely (II) [0 = 60° gauche] and (III) [0 = 180° gauche], both having fra 5-conformation may show the maximum biological activity. 

Following are some of the chemical parameters that have been put forward to buttress the above-mentioned facts. They are  

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