hydrogen transfer between the ends of three carbon atoms linked by one single and one double bond (Figure ). In these cases, CFB-ENM correlation terms force the path to pass through a structure resembling a four-membered ring (Figure center), which we term a quasi-four-membered ring (Q4MR). Such structures typically lead to significant bond angle strain, making them energetically unfavorable. Consequently, CFB-ENM paths involving Q4MRs likely have higher energy than FB-ENM paths. This view is further supported by the prevalence of reactions with non-C=CCH Q4MRs in the upper range of the energy difference distribution (Figure orange). The particularly large energy differences for C=CCH Q4MRs are likely due to π-conjugation making the carbon chain more rigid. Based on these findings, we have added an option to our CFB-ENM implementation to exclude Q4MR-generating correlation terms. The region unrestricted by these correlation terms is represented as a flat bottom, similar to FB-ENM. Thus, the bottom of the total energy, combining FB-ENM and correlation terms, becomes the intersection of FB-ENM's flat bottom and that of the correlation terms.