Proton donor molecule

The possible mechanism of ionization, fragmentation of studied compound as well as their desoi ption by laser radiation is discussed. It is shown that the formation of analyte ions is a result of a multi stage complex process included surface activation by laser irradiation, the adsoi ption of neutral analyte and proton donor molecules, the chemical reaction on the surface with proton or electron transfer, production of charged complexes bonded with the surface and finally laser desoi ption of such preformed molecules. 

Hydrogen bonding 5, occurs when a proton-acceptor molecule (primary and secondary amines, and sulfoxides) interacts with a proton-donor molecule (alcohols, carboxylic acids, and phenols). 

Proton landing defines the basicity of anion-radicals. This landing assumes 1 1 stoichiometry with respect to an anion-radical and a proton donor molecule. For example, in the reaction of the naphthalene anion-radical (CjoH ) with methanol, this 1 1 stoichiometry should result in the formation of 50 50% mixture of naphthalene (CjoHj) and dihydronaphthalene (CioHjo). 

For comparison, the authors have probed a complex formed by the same proton-donor molecule and molecular hydrogen. In this very weak complex, HCCH- - (H2), the H- - (H2) distance has been calculated as 2.606 A (i.e., significantly larger than the sum of the van der Waals radii of H). It is extremely interesting that a topological analysis of the electron density also leads to the appearance of the bond critical point in the H- - (H2) direction. However, the Pc and V pc values are very small (0.0033 and 0.0115 au, respectively) compared with those in the HCCH- - -HLi complex (0.0112 and 0.0254 au, respectively). The most important conclusion of this comparison is There is no evident borderline between the dihydrogen-bonded complexes and the van der Waals systems. 

TABLE 6.3. BSSE-Corrected Interaction Energies and H- -H Distances for Li and Na Dihydrogen-Bonded Complexes Formed with Various Proton-Donor Molecules ... 

TABLE 8.1. Acidity Factors Scaling Some Proton-Donor Molecules... 

Scheme 10.8 represents proton transfer to hydride ligands with the participation of two proton donor molecules, emphasizing the role of homoconjugated [X- H X] species in the kinetics of the process. Note that the second HX molecule initiates the formation of the solvent-separated or contact ion pair, corresponding to pathway (1) or (2). Following the principles of formal kinetics, pathway (1) can be expressed via... 

The results presented in this work show that in the linear structured water dimer the partitioned energy terms calculated for the proton donor and acceptor molecules are significantly different (except the kinetic energy). The electron structure of the proton donor molecule was found more compact than that of the acceptor subsystem, when compared their (partitioned) total energy EM values. This result is in an excellent agreement with our pre-vious results obtained on the separated molecular orbital energies [17]. 

The introduction of TA into the epoxide-primary amine system should lead to the inhibition of polycondensation due to a decrease in the concentration of the free proton-donor molecules due to their bonding to give nonreactive complexes with TA. Therefore, in the general case the curing rate in the presence of amine mixtures can be both" higher (as in the above case) and lower as compared with the primary... 

Proton acceptor. A functional group capable of accepting a proton from a proton donor molecule. 

Protophillic H-bond donor solvents solvents such as amides, amines or and other compounds with at least one N—II bond, which may be shared or donated. These solvents also have a highly basic character in the Bronsted sense i.e., they have a likelihood of accepting a free proton or a proton from a proton donor molecule (protophillic). These solvents also show high electron donor and acceptor properties (basic and acidic in the Lewis sense). 

Figure 6 compiles the theoretical and experimental data on the equilibrium geometry of (HF)2. It reveals the commonly expected features of an ordinary hydrogen bond the complex is planar and exhibits Cs-symmetry. A small elongation of the HF bond in the proton donor molecule relative to the bond in free HF is found. The inter-... 

First consider LSC systems where hydrogen bonding between solute and solvent molecules cannot occur (no proton-donor molecules). 

Morishima et al. (218-220) have continued their exhaustive study of the interactions of the nitroxide radical with a variety of closed-shell molecules. With proton donor molecules (X H) (e.g. CHCI3, CH2CI2) the low frequency shifts of the X-H proton and the high frequency shifts of the X portion are interpreted in terms of spin polarization of electron density from DTBN to X-H. Formation constants, enthalpies, and spin densities on the H and atoms for the H-bonded complex X H - DTBN have been evaluated. The spin delocalization mechanism involves positive spin density on DTBN being directly transferred on to the C-X antibonding orbital of the halogenomethane... 

The use of aliphatic and aromatic alcohols, amines, and carboxylic acids as proton donor molecules with DTBN reveals that whereas the X-H protons are shifted to low frequency by the radical the C-H protons, other than X-H, are moved to high frequency (223) (Table X). These high frequency shifts are shown to be characteristic of protic molecules and demonstrate conformational or geometrical dependences. Thus, protons lying on a zig-zag path from the -OH or -NH... 

DTBN-induced proton shifts in some proton donor molecules (223)... 

The simplest type of H-bond would be one in which the proton donor molecule contained only one hydrogen that could participate and the acceptor only one lone pair capable of in-... 

Substitution of one hydrogen of HOH with an aromatic group leads to a phenol molecule. When paired with methanol, phenol acts as the proton donor molecule in a structure very much akin to the water dimer itself At the SCF/6-31G level, the interoxygen distance is 2.89 A. The electronic contribution to the binding energy is computed to be 6.0 kcal/mol, after removal of BSSE, and 7.1 kcal/mol at the MP2 level with the same basis set. Correction of the correlated result by ZPVE yields a of 5.8 kcaPmol, leading to the conclusion that phenol is a more potent proton donor than is water. 

This work is counterpointed by a study of the analogous dimethylamine dimer in the gas phase " in which the authors deduce a geometry that appears to contain a distorted linear H-bond. That is, both the El atom of the proton donor molecule and the lone pair of the acceptor are bent to one side of the N--N internuclear axis. But this distortion is substantial, and the designation as linear type is not entirely clear indeed, the authors refer to their structure as cyclic although only one of the hydrogens can be conceivably involved in a H-bond. 

The reader may have noted that experi mental spectra of H-bonded species are com monly measured in either the gas phase or in inert gas matrices. Of course, there may be some differences as the molecules of the matrix can interact in various ways with the H-bonded complex. A recent set of measurements provides some estimates as to the perturbations caused by the matrix. Table 3.39 reports in the first row the frequencies of the OH stretches of the free and bridging hydrogens of the proton donor molecule of the water dimer in the gas phase. The next row indicates that a Ne matrix has only a very small effect, perhaps 10 cm . The Ar and Kr matrices produce larger perturbations, reducing the frequencies by about 30 cm . A smaller cluster of Ar atoms, averaging perhaps 50 such atoms yields a result very much like a full Ar matrix. With the single exception of the very small increase for the free OH stretch in the Ne matrix, all matrices and the Ar cluster lower the frequencies of both of the modes studied. 

Table 3.39 Frequencies (cm ) measured for the proton donor molecule of the water dimer in various media .

The intermolecular frequencies in Table 3.72 are similar in pattern to other H-bonded complexes . The H-bond stretching frequency, in excellent agreement with experiment, is smaller than in HCN--HF or FH- NHj, consistent with a weaker bond. The highest intermolecular frequency is again the pivoting of the proton donor molecule. A comparison of SCF and MP2 data indicates that correlation does not have a profound effect upon these intermolecular frequencies. Its principal effect is an increase in the H-bond stretch frequency. The intensities in Table 3.73 are in keeping with comparable systems. The H-bond stretch is of low IR intensity, with the donor bend much stronger. 

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