Drago scale

Phosphorus-31. Similarly to proton, 31-phosphorus has an ideal isotopic natural abundance (100%) it has, however, a lower sensitivity (Yp/Yh = 0.40). Phosphine oxides, in particular triethylphosphine oxide (TEPO) is a powerful probe to evaluate the acidity of surface sites (Drago scale. Table 3)." As an example, it has been used to reveal surface sites in supported lanthanides." ... 

First of all, quantum calculations allow one to predict basicity scales in agreement with experiment provided that the calculations are performed on the preferred conformation of the isolated molecule. If this is not done, a given term within a consistent series may jump from one rank to another as a function of the conformation used for the calculations. The determinant role of preferred conformation on any property (barrier to internal rotation and inversion, dipole moment, first adiabatic ionization potential, acidity and basicity in the gas phase, energy of complexation to BF3, etc.) was clearly demonstrated. We further show the importance of the role of preferred conformation in explaining some of the anomalies in Drago s systematics. 

The double-scale four-parameter enthalpic equation proposed in 1965 (54) and successfully developed by Drago et al seems to be the best tool so far available for correlating and predicting the formation enthalpies of Lewis adducts in the gas phase or, if really necessary, in solution. 

R. S. Drago, B. B. Way land. A Double-Scale Equation for Correlating Enthalpies of Lewis Acid-Base Interactions. J. Am. Chem. Soc. 1965, 87, 3571-3577. 

It is tempting to correlate these E and C parameters with the concept of hard and soft acids and bases (see Section 8.1). This is difficult, however. The idea of hardness implies a single-parameter scale (although no satisfactory numerical scale of hardness/softness has yet been established) while the Drago approach requires two parameters for each acid or base (acceptor or donor). 

Drago s EJC analysis and Gutmann s donor/acceptor approach [53, 67] have been compared [200, 217, 218], Eq. (2-12) has been extended for specific and nonspecific interactions between solutes and polar solvents [219]. Various Lewis acidity and basicity scales for polar solvents have been examined and compared by Fawcett, who concluded that the donor/acceptor scales of Gutmann seem to be the most appropriate [341],... 

A double-scale enthalpy equation proposed by Drago and Wayland to correlate (and predict) the enthalpy of adduct formation in gas-phase or poorly solvating media [17,18] is given by ... 

In infrared (IR) spectroscopy, the best resolution we can achieve is an energy difference of 0.1 cm . The lifetime. At, corresponding to this energy difference is 5 x 10" sec. Because one needs a process that gives rise to lifetimes of 10 or less to cause broadening—much less eventual separation—of the bands, we will see only one peak corresponding to the classical description (Drago, 1977, pp. 86 87). In other words, a process—here, a vibration—that operates on this time scale, coupled with the limits of detection, causes the two states to appear as one. ... 

Drago, R. S. (1992). J. Org. Chem. 61, 6547. A paper dealing with the analysis of solvent polarity scales. 

The importanee of aeid-base interactions in various fields of ehemistry led to extensive research in the 1960s to obtain acid-base scales. This resulted in the Hard and Soft Aeids and Bases (HSAB) seales of Pearson [30], Drago s E and C eonstants [31], and Gutmann s donor and aeeeptor numbers [32]. Bolger and Miehaels [33] have used Bronsted acid base ehemistry to predict the adhesion of organie and inorganic species. 

Conversely, the AN seale ean be viewed as a scale of hardness for adds since EtsPO is a hard reference base. Nevertheless, the merit of Gutmann s approach Kes in the fact that his scales provide both addic and basic parameters for amphoteric species, which is not the case with Drago s E and C classifications. 

Drago developed a universal polarity scale (the S scale) from more than three hundred spectral data (electronic transitions, F and N chemical shifts and RSE coupling constants) for 30 solutes in 31 non-protic solvents from cyclohexane to propylene carbonate. He used the equation... 

Much attention has been given to correlating A// against properties of the interacting species. Two of the most common are the Gutmann [96] donor number, DN, or acceptor number, AN, scales and the Drago [97] E C formulation. The donor number, DN, quantifies the Lewis basicity of a variety of solvents and was defined for a given base B as the exothermic heat of its reaction with the reference acid, antimony pentachloride, in a 10 - M solution in a neutral solvent (1,2-dichloroethane). The units are (kJ/mol). Specifically ... 

Drago has proposed a "unified scale of solvent polarities" based on an extension of the E and C acid and base parameters discussed above. Each solvent is characterized by a parameter S and the change in some property, A%, of a probe system is given hy Ax = PS + W, where P and W are constants for Ae probe. If the probe is an acceptor (Lewis acid) in a donor solvent, then... 

It has been recognized that a two-parameter scale is necessary, in general, to correlate solvent basicityThe conditions under which a one-parameter correlation may appear to woric have been discussed by Drago. ... 

Several individuals have worked to quantify these trends, making scales of Lewis acidity and basicity. Gutmann has created a series of donor numbers (DN) and acceptor numbers (AN) for various solvents, while Drago and Wayland have assigned parameters E and C, which measure electrostatic interactions and covalent bonding potential, respectively. Lastly, Pearson treats each Lewis acid and base with two parameters, relating what is called the strength of the acid/base and the softness/hardness of the acid/base. In fact, the HSAB trend discussed above is primarily a concept developed by Pearson. 

In 1990, Drago and co-workers (104) had accumulated enough new information to warrant the assigning of improved values of the various Drago constants. The old iodine reference parameters (above) were changed to U = 0.5 (kcal/mol) and Ca = 2.0 (kcal/mol). This change expanded the Eb scale so that it covered a range comparable to the other parameters. 

Osegovic, J.P. and Drago, S.R. A solid acidity scale based on the P MAS NMR shift of chemisorbed triethylphopshine oxide. J. Catal 1999,182, 1-4. 

A unified scale of solvent polarities, taking into account both the non-specific and specific donor acceptor interactions of these solvents with solute probes, was introduced by Drago and co-workers and shown in its mathematical form below [17] ... 

Drago RS, Hirsch MS, Ferris DC, Chronister CW A unified scale of solvent polarities for specific and non-specific interactions. J Chem Soc Perkin Trans 2 1994, 2 219-230. 

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