Two gaseous alkenes, compound A (a perfectly linear chain) and compound B (a similar chain with a single 120° bend in the middle), each react with chlorine atoms in an elementary, one-step addition that requires the Cl atom to strike the terminal carbon–carbon π bond from an "end-on" direction.
A reactor is run at 400 K and 1.0 atm for each alkene separately. In both experiments the total collision frequency between Cl atoms and alkene molecules is 1.5×109 collisions s⁻¹. Assume that energy requirements are always satisfied at 400 K, so the orientation requirement is the only factor limiting reaction.
(a) For a molecule treated as a rigid rod, the probability that a randomly oriented attacker approaches "end-on" is 161. Using this model, calculate the expected number of successful collisions per second for compound A.
(b) Treat compound B as two rigid rods joined at a 120° angle. Assuming the attacker must still approach one of the terminal π bonds "end-on," show that the orientation probability is 81. (You may assume equal accessibility of both ends.)
(c) Using your result from part (b), determine the expected number of successful collisions per second for compound B and calculate the ratio rateArateB.
(d) Explain qualitatively why the presence of the bend in compound B doubles the orientation probability relative to the linear compound.