Hydration free energy difference of acetone, acetamide, and urea

Jedlovszky, Pál; Idrissi, Abdenacer

doi:doi:10.1063/1.2992584

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The Zeeman effect in the (0,0) band of the A ⁷Π−X ⁷Σ⁺ transition of manganese monohydride, MnH

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Phase separation under ultraslow cooling: Onset of nucleation

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The hydration free energy and hydration entropy difference of urea and acetone, and of acetamide and acetone have been calculated both by free energy perturbation and by the method of thermodynamic integration. The obtained results show a striking asymmetry between the thermodynamic changes accompanying the replacement of the first and second CH₃ group of acetone by NH₂. Thus, the first CH₃/NH₂ exchange is found to lead to an about 10 kJ/mol decrease in the energy, 8 kJ/mol decrease in the Helmholtz free energy, and 5–10 J/mol K decrease in the entropy of hydration, while similar values accompanying the second CH₃/NH₂ exchange are found to be about −65 kJ/mol, −35 kJ/mol and −100 J/mol K, respectively. These results indicate that the two NH₂ groups of the urea molecule have a strong synergetic effect on the thermodynamics of the hydration of urea. The fact that the replacement of the two CH₃ groups of acetone by NH₂ leads to a strong decrease in the hydration entropy indicates that urea clearly has an ordering effect on nearby water.

Article Outline

INTRODUCTION
METHODS
1. Molecular models
2. Free energy perturbation
3. Thermodynamic integration
4. Monte Carlo simulations
RESULTS AND DISCUSSION

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KEYWORDS and PACS

Keywords

chemical exchanges, entropy, free energy, organic compounds, solvation, thermochemistry

PACS

82.60.-s

Chemical thermodynamics
82.30.Nr

Association, addition, insertion, cluster formation
82.30.Hk

Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.2992584

PUBLICATION DATA

ISSN

0021-9606 (print)

1089-7690 (online)

Publisher

$abstract.society.value is a Member of CrossRef

American Institute of Physics

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