Ab Initio Study of Substitution Effect and Catalytic Effect of Intramolecular Hydrogen Transfer of N-Substituted Formamides

Abstract

Intramolecular hydrogen transfer of N-substituted formamides has been examined by ab initio theoretical calculation. The potential surfaces, the global isomeric structures, and the transition geometries of intramolecular hydrogen transfer were determined at the MP2/6-31+G** level of calculation. The energy was further analyzed by a single point calculation, MP2/6-311++G**//MP2/6-31+G**, and the use of G2 theory. There are E and Z conformations in each substituted derivative. The calculated energy barrier for the intramolecular hydrogen transfer (carbon−hydrogen to the carbonyl oxygen) of formamide is 76.14 kcal/mol. The Z form of N-substituted formamides (regardless of the type of substituents, CH3, OH, and OCH3) all have lower barriers; nevertheless, the E form counterparts show significant substitution effect. The methyl group decreases the barrier by 1.35 kcal/mol, while the hydroxy and methoxy groups increase the barriers by 2.40 and 1.69 kcal/mol, respectively. The catalytic effect achieved by the added H2O or NH3 molecule to the formamides is substantial. Energy barriers decrease around 26.5∼30.1 kcal/mol in most of the complexes and the transfer mechanism of each complex is concerted.

C2H5NO Isomers: from Acetamide to1,2-Oxazetidine and Beyond

“…The conformer with cis Hs, technically this is the (Z ) conformer, is some 5.5 kJ mol −1 more stable than that with trans Hs or (E ) conformer in agreement with earlier work 57 and with a study of nitrogen species by a series of composite methods 58 where the difference was reported as 5.38 ± 0.8 kJ mol −1 at 298.15 K.…”

C2H5NO Isomers: from Acetamide to1,2-Oxazetidine and Beyond

“…The conformer with cis Hs, technically this is the (Z ) conformer, is some 5.5 kJ mol −1 more stable than that with trans Hs or (E ) conformer in agreement with earlier work 59 and with a study of nitrogen species by a series of composite methods 60 where the difference was reported as 5.38 ± 0.8 kJ mol −1 at 298. in accord with all recent theoretical determinations, viz. this work 9.79 eV, Frigge et al 13 9.80 eV.…”

Theoretical study of keto–enol tautomerism by quantum mechanical calculations (the QM/MC/FEP method)

“…Previous experimental studies using T‐jump relaxation methods provided evidence for this tautomeric process in what was called ‘bifunctional water‐catalyzed proton transfer’ because the water molecule acts as both proton donor and proton acceptor . Theoretical chemists have paid much attention to the role of solvent molecules in tautomeric and solvolytic reactions. More recently, proton transport catalyzed by neutral molecules has been suggested to occur during intramolecular proton transfer processes in protonated species or radical cations …”