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Strukturalne konsekwencje wiązania wodorowego

Krygowski T.M., Szatyłowicz H.

Wiadomości Chemiczne

2011

[Z] 65, 11-12

953-974

Hydrogen bonding belongs to the most important chemical interactions in life and geochemical processes as well as in technologies, that is documented in many review articles [1-10], monographs [11-17] and numerous publications. Figure 1 presents how "popular" are studies concerning hydrogen bonds (the term H-bond/bonding/bonded in a title, key-words or in abstract) in the last decade. First information about H-bond formation appeared at the end of XIX and a few other at beginning of XX centuries [19-24]. Most common definition of H-bonding stems from Pauling [27], whereas the newest IUPAC definition was published very recently [26]. Most frequently H-bonding is experimentally described by geometry parameters [28, 32] - results of X-ray and neutron diffraction measurements, but NMR and IR/Raman spectroscopies are also in frequent use. Characteristic of interactions by H-bonding is usually discussed in terms of energies [29-31], with use of various quantum chemical theories [54-57] and applications of various models as AIM [35, 41, 42, 45-48] and NBO [43, 44] which allowed to formulate detailed criteria for H-bond characteristics [35, 48]. H-bonds are classified as strong, mostly covalent in nature [7, 29, 34], partly covalent of medium strength [35] and weak ones, usually non-covalent [7, 29, 34, 35]. Theoretical studies of H-bonding mainly concern equilibrium systems, however simulation of H-bonded complexes with controlled and gradually changing strength of interactions [61-71] are also performed. The latter is main source of data referring to effect of H-bonding on structural properties: changes in the region of interactions, short and long-distance consequences of H-bonding. Application of the model [61] based on approaching hydrofluoric acid to the basic center of a molecule and fluoride to the acidic one, (Schemes 2 and 3) allows to study changes in molecular structure of para-substituted derivatives of phenol and phenolate [62, 64] in function of dB…H, or other geometric parameter of H-bond strength (Fig. 2). It is also shown that CO bond lengths in these complexes is monotonically related to H-bond formation energy and deformation energy due to H-bond formation [65]. Alike studies carried out for para-substituted derivatives of aniline and its protonated and deprotonated forms [77, 78, 81] give similar picture (Fig. 3). AIM studies of anilines [77, 78] lead to an excellent dependence of logarithm of electron density in the bond critical point and geometric parameter of H-bond strength, dB…H presented in Figure 4. Substituents and H-bond formation affect dramatically geometry of amine group [66] in H-bonded complexes of aniline as shown by changes of pyramidalization of bonds in amine group (Fig. 5). Some short- and long-distance structural consequences of H-bonding are shown by means of changes in ipso angle (for amine group) in the ring and ipso-ortho CC bond lengths (Fig. 6). Moreover, the mutual interrelations are in line with the Bent-Walsh rule [84, 86]. Changes of the strength of H-bonds in complexes of p-substituted aniline and its protonated and deprotonated derivative are dramatically reflected by aromaticity of the ring66 estimated by use of HOMA index [87, 88] (Fig. 7), where strength of H-bonding is approximated by CN bond lengths. Scheme 4 presents application of the SESE [91] (Substituent Effect Stabilization Energy) for description in an energetic scale joint substituent and H-bond formation effects.

Naturalne orbitale wiązań : metoda NBO

Wojciechowski P. M.

Wiadomości Chemiczne

2005

[Z] 59, 3-4

193--212

Natural bond orbital (NBO) analysis based on Löwdin's concept of "natural'' orbitals [1] is used to describe the unique set of orthonormal 1-electron functions and to express the density θ(r) of ρ(r) Ψ. Natural bond orbitals are typically localized orbitals and provide the most accurate possible "natural Lewis structure'' pattern of Ψ, because all orbital details like polarization coefficient or atomic hybrid composition are mathematically chosen to include the highest possible percentabe of the electron density [2]. This concept adapted by Frank Weinhold and co-workes in NBO's package [3] provides the information about charges, bond types, hybrid directions, resonance weights, bond orders, etc. The NBO program comprises a sequence transformation from the input basis set to various localized basis sets, including natural atomic (NAO), hybrid (NHO), and (semi-)localized molecular orbital (NLMO) sets. Widespread acceptance of the NBO paradigm by scientist in all fields of chemistry results in over 500 published applications per year. NBO-based techniques are being employed from donor-acceptor intermolecular interaction [4], and particular effectiveness in elucidating resonance-type stereoelectronic and steric factors, to nature of H-bonding in clusters, liquids and enzymes [5], and analysis of electronic principles of photexited and radical species.