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Conformational preferences in alkylbenzenes and aryl‐alkylamines: A comparative study using CAMSEQ, MM2 and molecular dynamics methods
Author(s) -
Grunewald Gary L.,
Creese Mary W.,
Weintraub H. J. R.
Publication year - 1988
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.540090406
Subject(s) - alkylbenzenes , conformational isomerism , chemistry , aryl , alkyl , protonation , molecular dynamics , ring (chemistry) , hydrogen bond , computational chemistry , stereochemistry , crystallography , molecule , organic chemistry , ion , benzene
Conformational preferences in a series of alkylbenzenes and protonated and neutral aryl‐alkylamines of biological interest have been examined. First, a general picture was obtained for the 25 compounds in the series by means of the CAMSEQ empirical potential software system. This provided solution as well as vacuum data. A low‐energy “folded” conformation (alkyl chain coiled toward aromatic ring) was observed in every case. The presence of an amino nitrogen atom in the alkyl chain did not significantly influence conformational preference. Secondly, a group of 14 compounds, representative of the subgroupings within the main series, was selected and the previously established (CAMSEQ) folded and extended minimum positions were further examined by means of a modified MM2 program. Energy differences between conformers were also calculated, and the presence of a stable folded form was confirmed. A feature common to many of the folded conformations is the positioning over the ring of a hydrogen atom from the terminal group of the chain. The MM2 folded/extended energy differences were in some cases smaller than those determined by CAMSEQ, with the “extended” form in many cases being about 1 or 2 kcal/mol more stable. Thirdly, three representative compounds from the series were examined by means of a molecular dynamics program which permitted the sampling of conformational space throughout the transition from extended to folded forms. This method gave energy differences between folded and extended conformations which agreed with the corresponding MM2 differences.