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1 H NMR lanthanide‐induced shift (LIS) investigations of highly flexible molecules—a new approach. Part II
Author(s) -
Lehmann J.,
Kleinpeter E.
Publication year - 1993
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260310411
Subject(s) - dihedral angle , chemistry , maxima and minima , lanthanide , molecule , proton nmr , gradient descent , computational chemistry , crystallography , stereochemistry , organic chemistry , mathematical analysis , computer science , hydrogen bond , artificial intelligence , ion , mathematics , artificial neural network
A new method and computer program for LIS calculations of highly flexible molecules was developed using molecular geometries obtained by randomly varied dihedral angles (up to ten angles rotating freely and independently from each other are possible) as start conformations for a STEEpest Descent (STEED) search algorithm to find minima characterized by the R factor at the ‘LIS R factor hyper surface.’ This STEED–LIS method allows easy, accurate and rapid access to the probable global minimum of the R factor depending on up to ten variable dihedral angles. This means that LIS investigations of highly flexible molecules with more than one freely rotating dihedral angle are no longer complicated and time consuming, but can be carried out automatically using the developed programs [JLLISSD (with interactive parameter dialogue) and LISSDEMU (using parameter input files prepared by LISSDINP)]. The results obtained are in very good agreement with known or reported preferred conformations of the investigated test compounds, propan‐1‐ol, butan‐1‐ol and ethyl p ‐methoxycinnamate.