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Evaluation of MINDO /3 calculated structures. II. Branching errors in alkanes and cycloalkanes
Author(s) -
McManus Samuel P.,
Smith Maurice R.,
Smith Margaret B.,
Shafer Steven G.
Publication year - 1980
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540010304
Subject(s) - mindo , chemistry , mndo , branching (polymer chemistry) , vicinal , standard enthalpy of formation , computational chemistry , isomerization , geminal , molecule , stereochemistry , organic chemistry , catalysis
MINDO/3 calculations have been carried out for a series of branched chain alkanes in order to assess effects of branching on calculated geometries and heats of formation (Δ H f ). With vicinal branching, MINDO/3 calculates the central CC bond to be too long. Bond angles are also found to be distorted. Errors in calculated heats of formation are large when geminal branching is present and significant with vicinal branching. Branching error corrections for Δ H f have been derived and applied to a separate series of branched acyclic and cyclic compounds. For the test sample, application of the branching error corrections gave calculated structures of acyclic branched hydrocarbons with heats of formation having an average absolute error of 1.3 kcal/mole rather than 17.3 kcal/mole before correction. Cyclic branched hydrocarbons are shown to be less well corrected. Calculations of heats of reaction have also been carried out for some isomerization and cyclization reactions using the MINDO/3 and MNDO methods. It is clear from the comparisons that MNDO calculations give less severe errors for highly branched compounds but the errors are still substantial. For prediction of heats of reaction, the error‐corrected calculations are shown to be superior to the “raw” calculations obtained by MINDO/3 or MNDO.