THEORETICAL-STUDIES OF ELIMINATIONS .5. INTERMOLECULAR VS INTRAMOLECULAR ELIMINATIONS - AN AB-INITIO STUDY OF THE GAS-PHASE REACTION OF NH2- WITH CH3CN2SCH3

Ab initio calculations at the MP2/6-31+G*//MP2/6-31+G* level have bee n completed on the title reaction. The computational results are in go od accord with a mechanism suggested by Nibbering and co-workers in 19 87. The preferred elimination pathway involves abstraction of an alpha -proton followed by an intramolecular syn elimination. Although a conv entional E2 mechanism is viable, abstraction of an alpha-proton has a substantial energetic advantage and is effectively irreversible. The i ntramolecular syn elimination has a higher barrier than a conventional anti E2 pathway, but is the only option after the irreversible alpha- proton abstraction. Results are also presented for the reaction of flu oride with CH3CH2SCH3.