H-bonded complexes

Shinohara, N. Nishi, and N. Washida, Chem. Phys. Lett., 1984, 106, 302. 

study of hetero-dimers formed from HCl, DCl, HF, and DF with (CH3)20, CH3OH, and (CH3)3COH Vibrational predissociation in HF.O(CH3)2 t I.r. absorption spectra of (H20)2 measured in the region of the O-H stretch by monitoring predissociation Rotational spectra and constants for HjO.HCN t Two-photon MPI/m.s. study of NHj clusters t VUV photoionization/m.s. study. Observation of unprotonated cluster ions (NHjlJ and (NHj) in addition to (NH3)2 and 

Vibrational predissociation of glyoxal.H2 complexes studied for several vibrational levels of the first excited singlet state of glyoxal 

Laser T-jump and shock-tube study of the lifetime of the acetic acid dimer 

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We have proposed an initiation mechanism for the ROOH-amine system in which some H-bond complex may be formed [36]. Then Sun et al. [37,38] thoroughly investigated the initiation mechanism of ROOH-Amine through IR spectra of TBH-triethylamine, TBH-DMT, and CHP-DMT. From the wideness of the shift of OH absorption bands at 3120, 3336, and 3257 cm were... 

The reaction is generally believed to proceed via the formation of ionic acylam-monium intermediate compounds (Reaction 1, Scheme 2.27). The equilibrium constant of the acylammonium formation depends mostly on steric and resonance factors, while the basicity of the tertiary amine seems to play a secondary role.297 In die case of the less basic compounds, such as acidic phenols, and of strong tertiary amines, such as Uialkylamines, the reaction has been reported to proceed through a general base mechanism via the formation of hydroxy-amine H-bonded complexes (Reaction 2, Scheme 2.27).297... 

Hydroxy-amine H-bonded complexes, 76 Hydroxybenzoic acids, polyesterification of, 79... 

Binding constants of H-bond complexes are normally used to create H-bond scales [21-23], e.g. in accordance with Ref [22] ... 

Figure 3.12. Optimized structure of the free triplet state (a) and the triplet of the carbonyl H-bond complex (b) calculated from the DPT calculations using the UB3LYP method with a 6-311G basis set. (Reprinted with permission from reference [42]. Copyright (2005) American Chemical Society.)...

Tuma, C., Boese, A. D., Handy, N. C., 1999, Predicting the Binding Energies of H-Bonded Complexes A Comparative DFT Study , Phys. Chem. Chem. Phys., 1, 3939. 

Figure 1.18 STM image (4 nm x 4 nm) showing the 2D cocrystalline structure consisting of an ordered array of 1 1 H-bonded complexes of (R,R)-tartrate and methylacetoacetate species on Ni l 1 1 givingachiral (3 11-3 4) structure. (Adapted with permission from Ref. [62], Copyright 2002, Elsevier.)...

Experimental determinations undertaken prior to the discovery of electrospray as a source of ions have shown86 87 that the bond strength of H-bonded complexes XH —A" increases with the gas-phase acidity of XH and the gas-phase basicity of A-. This relation has been examined82 for the special case where A- were a variety of anions produced by electrospray and XH = OH2, on the basis of the hydration energy data (see Table 8) and gas-phase basicities AGj A-) = AG°cid (AH) corresponding to the free energy change for the gas-phase reaction ... 

Basch, H., and W. J. Stevens. 1990. The Structure of Glycine-Water H-Bonded Complexes. Chem. Phys. Letters 169, 275-280. 

Note that the molecules in gaseous phase do not exchange energy with the thermostat so that expression (4.2.17) corresponding to the limiting case ijj — 0 is consistent with the concept of hot electrons (with the frequencies coh + Z,/j4A 1 - )) which accounts for the fine structure of spectral lines of gaseous H-bond complexes.155 The one-sided broadening of the spectral line 2f is proportional to the... 

The simple iib-ctah predictions (5.30a)-(5.30e) can be tested and compared with expectations of classical electrostatic models for each of the H-bonded complexes to be discussed below. 

Table 5.3. The NBO descriptors of binary B HA H-bonded complexes (see Fig. 5.1), showing net intermolecular charge transfer A0b a, ctah bond ionicity / ah. and PNBO overlap integrals for attractive ri j ctah ( Vncr.) and repulsive iib-ctah (5no ) interactions...

We can also examine isomeric pairs of H-bonded complexes in which the roles of electron-pair donor and acceptor are reversed, and the mutual dipole orientations are therefore fundamentally altered. As an example, Fig. 5.4 shows the isomeric pair of complexes between ammonia and hydrogen fluoride,... 

Hydrogen bonds to water are of special importance because of their pervasive role in aqueous solution phenomena. Some general trends in H-bonding to water can be illustrated by the series of binary H-bonded complexes... 

Problem Use the data in Tables 5.7 and 5.8 and Figs. 5.5 and 5.7 to estimate the relative importance of donor-acceptor interactions in neutral versus ionic H-bond complexes. 

Figure 5.9 displays the equilibrium structures assumed by these cation-assisted H-bond complexes, and Table 5.12 summarizes energetic and structural properties... 

Table 5.15. A comparison of neutral and charged H-bond complexes B- -HA from Sections 5.2.1 and 5.2.2 (ordered by H-bond strength), showing net H-bond energy A hb, leading cr stabilization AEn fr2 net charge transfer 0b->-ah, and NRT bond orders bA—h and b-h...

Table 5.15 compares the neutral and charged H-bonded complexes of Sections 5.2.1 and5.2.2,ordered by H-bond strengthfrom weakest (H20- H4C) to strongest (F- H- -F ). For each B- -AH complex, the table shows the total charge, the energy of the H-bond (A Hb) and the leading n->-cr stabilization (AE fr2 ). 

As shown in Fig. 5.36, / R and vy become equal near s 0.6, whereas the charge transfer is half-complete near s — 0.3, and the energetic TS is at 5 = 0. Different criteria therefore lead to different estimates of the progress of reaction, but by all criteria the shifts of partial charge and covalency are quite pronounced in the H-bonded complexes. The net charge transfer gH to the evolving hydride Lewis base is seen to parallel bow closely, as the resonance picture (5.68a) suggests. 

Finally, Fig. 5.37 displays the bond-order-bond-length relationship for O- H and H H bonds over the entire range of the proton-transfer reaction. Both curves display nonlinear dependences tending to Rm oo as ab- 0, and to the standard single-bond distance as The points for the H-bonded complexes (those... 

Thus, by virtue of the continuity of the bond-order-bond-length relationship across the entire proton-transfer region, the interpretation of the H-bonded complexes in terms of partial proton transfer (with associated charge and covalent-bond transfer) can hardly be avoided. (Additional discussion of the properties of transition-state species in relation to the associated reactant and product species will be presented in Section 5.4.)... 

In summary, we may say that the NBO/NRT description of partial proton transfer in the equilibrium H-bonded complex(es) is fully consistent with the observed behavior along the entire proton-transfer coordinate, including the transition state. At the transition state the importance of partial co valency and bond shifts can hardly be doubted. Yet the isomeric H-bonded complexes may approach the TS limit quite closely (within 0.2 kcal mol-1 in the present example) or even merge to form a single barrierless reaction profile (as in FHF- or H502+). Hence, the adiabatic continuity that connects isomeric H-bond complexes to the proton-transfer transition state suggests once more the essential futility of attempting to describe such deeply chemical events in terms of classical electrostatics. 

Although transition metals M are not considered as standard hydrogen-bonding partners, they exhibit a number of properties that favor H-bond complexation to suitable Lewis acids or bases, namely... 

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