Comparison between some semi-empirical andab initio Hartree-Fock models for the description of amides (formamide revisited)

Autor:	L. W. Jenneskens, J. N. Louwen
Rok vydání:	1990
Předmět:	Formamide Basis (linear algebra) Chemistry Organic Chemistry Hartree–Fock method Ab initio MNDO Molecular physics Planarity testing chemistry.chemical_compound Computational chemistry Physical and Theoretical Chemistry MINDO Basis set
Zdroj:	Journal of Physical Organic Chemistry. 3:711-722
ISSN:	1099-1395 0894-3230
DOI:	10.1002/poc.610031104
Popis:	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 pπ 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.
Databáze:	OpenAIRE
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