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Comparison between some semi‐empirical and ab initio Hartree–Fock models for the description of amides (formamide revisited)
Author(s) -
Louwen J. N.,
Jenneskens L. W.
Publication year - 1990
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.610031104
Subject(s) - mndo , chemistry , basis set , formamide , ab initio , mindo , computational chemistry , amide , basis (linear algebra) , planarity testing , molecule , crystallography , density functional theory , organic chemistry , geometry , mathematics
Abstract A comparative study on the use of the MINDO/3, MNDO and AM1 semi‐empirical methods for the description of formamide and aliphatic amide systems is reported. For formamide, ab initio Hartree–Fock calculations are also reported using both the STO‐3G and 3–21G basis sets, as well as a basis set obtained by a minimal relaxation of the STO‐3G contraction scheme. It is shown that both the MNDO and the STO‐3G methods cannot properly reproduce the experimental results. In both cases this appears to be due to inadequacies of the basis sets used. Again in both cases only small improvements in the basis set necessary to allow for the diffuse character of the p π orbitals lead to dramatic improvements in the calculated results. In the case of the STO‐3G basis set this is demonstrated by the fact that a small relaxation in the contraction leads to results even superior to those with the 3–21G set. The conclusions reached for amide systems can be extended to other systems where planarity around or inversion with respect to nitrogen is an issue. This is demonstrated for ammonia.