ISSN:
0020-7608
Schlagwort(e):
Computational Chemistry and Molecular Modeling
;
Atomic, Molecular and Optical Physics
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
Notizen:
Ab initio calculations have been performed to investigate hydrogen bonding and ion-molecule association in complexes of H2O with the neutral, protonated, and Li+ complexes of N-formylformaldehyde and N-formylformamidine. In the complexes with the neutral bases, H2O assumes an in-plane bridging position in the amide and amidine regions. The most stable complex is the bridging N-formylformamidine-H2O complex in the amidine region, which has an MP2/6-31 + G(d,p) binding energy of -9 kcal/mol. Hydrogen bonded complexes of H2O with the oxygen-protonated bases have open structures with the protonated bases as proton donors, and binding energies ranging from -16 to -24 kcal/mol. Nitrogen protonation of N-formylformamidine leads to an equilibrium chelated hydrogen bonded structure with a stabilization energy of -21 kcal/mol. When Li+ associates with these bases at a carbonyl oxygen, hydrogen-bonded bridging structures with H2O reappear, and wobble complexes exist in the amide and amidine regions of N-formylformaldehyde and N-formylformamidine. These complexes have binding energies of -13 to -14 kcal/mol. However, the most stable comples has H2O directly bonded to Li+, with an MP2 binding energy of -30 kcal/mol. No hydrogen bonded structures of H2O with N-formylformamidine exist in the amide region when Li+ associates with this base at the C=N group. Hydrogen bond energies computed at the single-determinant Hartree-Fock level with the 6-31G(d) basis set approximate correlated MP2/6-31 + G(d, p) energies to within 1 kcal/mol for all of the neutral and charged complexes. However, when H2O is bonded to Li+, HF6-31G(d) association energies overestimate MP2/6-31 + G(d, p) energies by 3 kcal/mol.
Zusätzliches Material:
8 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/qua.560340712
