What Would Be the Molecularity of A Reaction Having Two Rate Determining Steps? A Conceptual Analysis

One of the conclusions of C Stegelmann’s, JACS article titled "Degree of Rate Control: How Much the Energies of Intermediates and Transition States Control Rates” is that the ‘degree of control of reaction’ is a concept similar to the concept of the ‘rate determining step’ but more direct to apply and much more widely applicable (since there is rarely a single rate determining step). Thus, an important inference from this JACS article is that a reaction having two or more rate determining steps in its multistep mechanism is in the realm of possibility. Can we write the molecularity of such reactions (that is a reaction having two or more rate determining steps)? The answer to this question and its implication is probed in this conceptual analysis. An important spin-off, of the answer to this question is that, the age-old classic substitution nucleophilic unimolecular i.e., SN1 reaction between tertiary butyl bromide and water being termed as ‘unimolecular’ in many textbooks and the entry in the Wikipedia is incorrect. The authors are of the opinion that this article should be discussed when SN1 reaction is taught at undergraduate level.