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Thermodynamic functions of conformational changes, part IV: Functional analysis of conformational entropy of substituted ethane and methanol
Author(s) -
Viskolcz Béla,
Szori Milan,
Izsak Robert,
Fejer Szilard N.,
Csizmadia Imre G.
Publication year - 2007
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.21319
Subject(s) - dihedral angle , chemistry , enthalpy , thermodynamics , conformational entropy , maxima and minima , entropy (arrow of time) , configuration entropy , computational chemistry , crystallography , physics , molecule , hydrogen bond , mathematics , mathematical analysis , organic chemistry
The thermodynamic functions Δ H and Δ S , were computed along the dihedral angle ( x ) of conformational change for a few selected single rotors: YCH 2 CH 2 Y and YCH 2 OH. The computations were carried out at the B3LYP/6–31G(d,p) level of theory, with 5° increments in x , under very tight optimization condition. The entropy function, S ( x ), was generated for the full range (0° to 360°) of internal rotation and was subjected to functional analysis. We found the general rule that S ( x ) had critical points at or near the critical points of Δ H ( x ); therefore, (d S /d x ) vanished for all critical points (minima and transition states) of Δ H ( x ). However, the entropy derivative also vanished at certain characteristic conformations that were not manifested on the potential energy or enthalpy function. These geometries were classified as “latent minima” or “latent critical points.” The conformational entropy change was related to the relative information ( I / I 180 ) of the same state, where the reference state was chosen to be the anti conformation ( x = 180°). According to the relationship ln( I / I 180 ) = −Δ S / R , information accumulation was observed in the case of 1,2‐disubtituted ethane and information depletion occurred in the case of fluoromethanol and ethyl alcohol. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007