Ideally, if the constraint violation of FB-ENM or IDPP were zero, this angle would be preserved along the path. Fiure 10g shows that, while FB-ENM keeps the O-C-H angle nearly constant as intended, IDPP fails to fully resolve the violation, and the three atoms temporarily align almost linearly. However, this linear structure appears to be energetically more favorable, and the energy maximum is lower for the IDPP path (Figure ). Thus, this reaction is a rare case where the unintended molecular distortion in the IDPP path works energetically in its favor.