Uggerud, Einar How Persistent Is Cyclopropyl upon Nucleophilic Substitution, and Is Frontside Displacement Possible? A Model Study Quantum chemical model calculations (MP2/6-31G(d,p)) demonstrate that frontside nucleophilic substitution is not possible in the reaction between water and protonated cyclopropanol. Instead, ring opening occurs, in accordance with a well-known disrotary ring-opening mechanism. When the cyclopropane ring is embedded in a stabilizing bicyclic structure, as in protonated bicyclo[3.1.0]hexanol, the mechanistic landscape changes. In this case frontside nucleophilic substitution occurs, and has a potential energy barrier which is lower than that of the corresponding backside substitution, which implies that the stereochemical outcome of this gas-phase nucleophilic substitution reaction is uncoupled from its kinetic order. This and similar results challenge the traditional view that nucleophilic substitution reactions should be categorized as being either S<sub>N</sub>1 or S<sub>N</sub>2. Frontside Displacement;protonated cyclopropanol;stereochemical outcome;landscape changes;nucleophilic substitution reactions;bicyclic structure;Nucleophilic Substitution;frontside nucleophilic substitution;backside substitution;ring opening;cyclopropane ring;Model Study Quantum chemical model calculations;energy barrier;results challenge;MP;S N 1;case frontside nucleophilic substitution 2001-09-20
    https://acs.figshare.com/articles/journal_contribution/How_Persistent_Is_Cyclopropyl_upon_Nucleophilic_Substitution_and_Is_Frontside_Displacement_Possible_A_Model_Study/3689835
10.1021/jo010546j.s001