Incumbrance area

Molecular size J, incumbrance area of planar molecule <100 or >135 A2 Affect absorption and metabolic activation... 

Since there is a molecular size and shape requirement for tumor induction by PAHs, either modifying (a) the size of the incumbrance area of planar molecule to < 100 or >135 A2, (b) the shape to contain more than four fused, linearly oriented rings, or (c) the structure to be symmetric will make the chemical less favorable for absorption, enzyme activation, and DNA interaction. 

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