Thermodynamics hydrogen bonding

HYBOT-Plus (hydrogen bonding thermodynamics, calculation of local and molecular physicochemical descriptors) http //www.timtec.net/soJiware/hybot-plus.htm... 

HYBOT Hydrogen Bond Thermodynamics LCAP Long-chain arylpiperazine... 

Raevsky OA, Skvortsov VS (2002) 3D hydrogen bond thermodynamics (HYBOT) potentials in molecular modelling. J Comput Aided Mol Des 16(1) 1-10... 

From 163 calculated H-bond donor and 195 calculated H-bond acceptor factors, one can get enthalpy and free energy values for 31785 reactions using Eqs. (3) and (4). Later, the number of H-bond factor values was significantly increased. A special program for calculating factor values was created and included in the HYBOT (Hydrogen Bond Thermodynamics) program [28, 29]. The current version, HYBOT-2006, has about 20000 values of H-bond acceptor factors and about 5000... 

Raevsky, 0. A., Grigor ev, V. Ju., Trepalin, S. V. HYBOT (Hydrogen Bond Thermodynamics) program package. Registration by Russian State Patent Agency N 990090 of 25 February 1999. 

Suresh, S J. and Naik, V.M. 2000. Hydrogen bond thermodynamic properties of water from dielectric constant data. J. Chem. Phys. 113, 9727-9732. 

Several X-ray structures have proved that under various conditions (e.g. condensation under alkaline or slightly acidic conditions) exclusively the C4-symmetrical isomer is formed,212,213 in agreement with semiempirical calculations. Most probably this is due to its stabilization via four intramolecular O-H-O hydrogen bonds (thermodynamic aspect), while a rapid isomerization (kinetic aspect, see Figure 21) remedies wrong structures formed during the synthesis. 

If one would ask a chemist not burdened with any knowledge about the peculiar thermodynamics that characterise hydrophobic hydration, what would happen upon transfer of a nonpolar molecule from the gas phase to water, he or she would probably predict that this process is entropy driven and enthalpically highly unfavourable. This opinion, he or she wo ild support with the suggestion that in order to create room for the nonpolar solute in the aqueous solution, hydrogen bonds between water molecules would have to be sacrificed. 

The amide formation reaction (highlighted by the circle) leads to the production of a hydrogen-bonded dimer (ZZ) of the reaction product Z with the template Z. The dimer is in thermodynamic equilibrium with free template in the reaction medium. 

Thermochemistry. Thermodynamic considerations ate of utmost importance in fluorinations. Table 1 is based on JANAF data (25) for CH, which indicate an average carbon-hydrogen bond strength of 410.0 kj/mol (98 kcal/mol) based on the atomization energy of CH. ... 

Thermodynamic and physical properties of water vapor, Hquid water, and ice I are given ia Tables 3—5. The extremely high heat of vaporization, relatively low heat of fusion, and the unusual values of the other thermodynamic properties, including melting poiat, boiling poiat, and heat capacity, can be explained by the presence of hydrogen bonding (2,7). 

Specific alterations of the relative reactivity due to hydrogen bonding in the transition state or to a cyclic transition state or to electrostatic attraction in quaternary compounds or protonated azines are included below (cf. also Sections II, B, 3 II, B, 5 II, C and II, F). A-Protonation is often reflected in an increase in JS and therefore the relative reactivity can vary with the significance of JS in controlling the reaction rate. Variation can also result from rate determination by the second stage of the SjjAr2 mechanism or from the intervention of thermodynamic control of product formation. Variation in the rate and in the reactivity pattern of polyazanaph-thalenes will result when nucleophilic substitution [Eq. (10)] occurs only on a covalent adduct (408) of the substrate rather than on its aromatic form (400). This covalent addition is prevented by any 4-... 

It should be mentioned that in the last few years super-cooled water has attracted the interest of many scientists because of its exceeding properties and life at temperatures below 0 °C 1819). Speedy recently published a model which allows for the interpretation of the thermodynamic anomalies of supercooled water 20). According to this model there are hydrogen bonded pentagonal rings of water molecules which have the quality of self-replication and association with cavities. 

Once such a molecular complex with hydroquinone has been formed it may persist under conditions where it is no longer thermodynamically stable. Because the molecules of the second component are enclosed in the cavities they cannot escape without breaking a number of hydrogen bonds in the -hydroquinone lattice. This corresponds to a considerable energy of activation which may prevent the attainment of thermodynamic equilibrium. 

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