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Ab initio and density functional studies of cooperative hydrogen bonding in calix[4]-and calix[6]arenes

“…The deviation of these data from the value obtained by RHF/6-31G(d) (26.7 kcal/mole) is -6.2 kcal/mole, 7.2 kcal/mole, 0.2 kcal/mole, 4.9 kcal/mole, -1.3 kcal/mole, -2.3 kcal/mole, -2.0 kcal/mole, -1.4 kcal/mole, 4.1 kcal/mole, and -1.9 kcal/mole, respectively, or 23.2%, 27.0%, 0.8%, 18.4%, 4.9%, 8.6%, 7.5%, 5.2%, 15.4%, and 7.1%, respectively. One can conclude that the above-mentioned semiempirical methods (AM1 [1], PM3) and the RHF/6-31G(d)/RHF/STO-2G technique, as well as RHF/STO-2G, RHF/3-21G, and RHF/6-31G, provide information about the magnitude of changes in the H bond energy in the compounds under study, which is in reasonable agreement with the data of RHF/6-31G(d) calculations (Table 5) [1,12]. The ab initio methods of calculation, where geometry optimization is fulfilled in one approximation and the energy of a structure is calculated in another (in particular, at second order Möller Plesset level of theory), obviously slightly exaggerate the strength of H bonds in calix [4]arene; as a result, changes in H bond energy obtained by these methods approximate the value obtained by RHF/STO-2G.…”

“…The energies of cooperative hydrogen bonds in calix [4]arene and calix [6]arene were calculated by the procedure suggested by P. Grootenhuis [1] and applied previously [12]. At first we determined the energy of the neutral compound relative to the energy of the monoanion obtained by proton elimination from the optimized neutral structure of the cone conformer of calix [4]arene or compressed cone conformer of calix [6]arene and subsequently optimized with the same level of accuracy as for the neutral conformer (Grad RMS = 10 -6 Hartree/Bohr):…”

“…None of these works dealing with calixarenes has reported on hydrogen bond energy calculations, although this energy is the key factor of conformational stability and conformational lability of calixarenes with free hydroxyl groups [12] and their reactivity [11].The stability of the hydrogen bond in calixarene was correlated with the reaction route involving this compound when dialkoxydihydroxycalix[4]arene was synthesized from monoalkoxytrihydroxycalix[4]arene [11] (Fig. 1).…”

“…None of these works dealing with calixarenes has reported on hydrogen bond energy calculations, although this energy is the key factor of conformational stability and conformational lability of calixarenes with free hydroxyl groups [12] and their reactivity [11].…”

“…A few works are devoted to studies of calix [4]arenes and thiacalix [4]arenes by ab initio [7-9, 12, 13] and density functional [6][7][8][9]14] methods, and only one work deals with investigation of calix [6]arenes by these methods [13]. None of these works dealing with calixarenes has reported on hydrogen bond energy calculations, although this energy is the key factor of conformational stability and conformational lability of calixarenes with free hydroxyl groups [12] and their reactivity [11].…”