Energetics of Intramolecular Hydrogen Bonding in Di-substituted Benzenes by the ortho−para Method

Abstract

The energetics of intramolecular hydrogen bonds (H-bonds) is a subject of fundamental importance in chemistry and biochemistry. In contrast with intermolecular H-bonds, whose enthalpy can be determined by experiment or accurately evaluated through a supermolecular approach, there is no general accepted procedure to determine the enthalpy of an intramolecular H-bond. In this work, different ways for assessing the energetics of intramolecular H-bonds of selected aromatic systems were applied and compared. They include the widely used conformational analysis approach (cis−trans method), a recently proposed isodesmic reaction method, and a new procedure that we designate as the ortho−para method. Energy calculations were carried out at several theory levels, including a modified complete basis set extrapolation method (CBS-QMPW1), in which the geometries are based on MPW1PW91/aug-cc-pVDZ density functional theory optimizations. The obtained results, together with a simple dipole−dipole interaction model, help to explain why the enthalpies of intramolecular H-bonds are often overestimated by the cis−trans method. The results also show that intramolecular H-bond enthalpies based on the isodesmic reaction method may be unreliable. The ortho−para method, which can be applied when accurate theoretical or experimental standard enthalpies of formation are available, is probably the best way of estimating the enthalpies of intramolecular hydrogen bonds. Finally, our results illustrate the important role played by intramolecular H-bonds in the energetics of homolytic dissociation reactions involving di-substituted benzenes.

Strength of Si–H ⋯ B charge-inverted hydrogen bonds in 1-silacyclopent-2-enes and 1-silacyclohex-2-enes

“…Nevertheless, in spite of this, some additive schemes leading to numbers understood as interaction energies have been proposed. Among them, the so-called open-closed method [45,46] seems to be both the most popular [26][27][28][29][45][46][47][48][49][50][51][52][53][54][55][56][57][58] and straightforward. According to this method, the interaction energy is just a difference between total energies of the closed form of a molecule, i.e.…”

“…What is more, having one of these open systems already chosen, one encounters a new question, namely whether or not the geometry of the open system should be fully optimized [28,58]. Unfortunately, only in a small piece of articles where the open-closed method is utilized, this question is addressed [19,28,29,45,46,58].…”

“…Unfortunately, only in a small piece of articles where the open-closed method is utilized, this question is addressed [19,28,29,45,46,58]. Most likely, Schuster was the first who suggested [45] to use the open form having 'the least changes in molecular geometry besides a cleavage of the H-bond' pointing out that the open reference system 'need not be a local minimum of the energy surface' [46].…”

Energetics of 1-(aminophenyl)pyrroles: A joint calorimetric and computational study

“…The three 1-(aminophenyl)pyrrole isomers follow the same trend of diaminobenzene isomers in terms of thermodynamic stability: ortho-> meta-> para-. Applying the ortho-para method (enthalpic difference between the para-and the ortho-isomers) proposed by Estácio et al [38] and assuming a mean value of 230.1 kJ Á mol À1 for the D f H m ðgÞ of 1-(4-aminophenyl) pyrrole, the intramolecular hydrogen bond enthalpy obtained in this work for 1-(2-aminophenyl)pyrrole is 6.0 kJ Á mol À1 , almost half of the value calculated for 1,2-diaminobenzene [35], in which a double intramolecular N-HÁ Á ÁN hydrogen bond is considered.…”

An energy decomposition analysis study for intramolecular non-covalent interaction

“…The current theoretical schemes for intramolecular interactions can be divided into three categories. The first category is concentrated on interaction energy estimation, including the open-close (OC) method [1], the rotation barriers method (RBM) [2], the related rotamers (RRM) method [3,4], the orthopara (OP) method [5], the isodesmic/homodesmic reactions (ID) method [6], the molecular tailoring approach (MTA) method [7][8][9] and the natural bonding orbital (NBO) method [10][11][12] etc. Among them, the OC, RBM, RRM, OP, and ID methods are proposed for certain intramolecular hydrogen bonding systems.…”