Phenol experimental values

Estimated values using TD-DFT/B3LYP/6-311++G(d,p) calculations and a systematic correction based on a comparison of the calculated and experimental values for phenol. Experimental values are in parentheses. 

Table 5.7 Calculated Values of a and f for Phenol-formaldehyde Resins Formed from Different Proportions of Reactants and Based on Experimental Values of n and n .

Fig. 7. Dependence of relative molar concentrations n-Jn of reaction components on reciprocal space velocity W/F (hr kg mole-1) in the consecutive hydrogenation of phenol. Temperature 150°C, catalyst Pt-SiCh (1% wt. Pt), initial molar ratio of reactants G = 9. The curves were calculated (1—phenol, 2—cyclohexanone, 3—cyclohexanol) the points are experimental values. From Ref. (61). Reproduced by permission of the copyright owner.

Nucleophilic addition of phenolic nucleophiles to l,l-dicyano-2-arylethenes in the gas phase and in water has been studied theoretically" using the semiempirical AMI method and the Cramer-Truhlar solvation model SM2.1. The difference between the Brpnsted coefficients (a" = 0.81 and P" =0.65) determined for the gas-phase reaction is indicative of a small positive transition state imbalance of / = 0.16. For reaction in water the estimates (a" = 0.61 and P" = 0.36, giving I = 0.25) are close to the experimental values (a" = 0.55 and P" = 0.35) obtained with amine bases, and the small imbalance is as expected for a reaction involving no hybridization change at the incipient carbanion site. 

These place a positive charge on the oxygen atom of the unionized molecule, and so cause it to repel the proton. On analysis of the experimental values for Ka at 25°C it is found that the inductive effect of a nitro group increases Ka by a factor of about 45, and the resonance effect in the ortho and para positions gives another factor of about 22. The acid constant of a nitrophenoi can be found approximately by multiplying that for phenol, l.t X 10 10, by the factor 45 for every meta nitro group and 1000 for every ortho or para nitro group in the molecule. The comparison of the values calculated in this way with those found by experiment is shown in Table 8-1. ... 

Example 4b) Assuming no experimental values of Kow or S are available, estimate Koc for 2,6-di(tert-butyl) phenol from MCIs using the following expression (Meylan et al., 1992) ... 

The reaction of ozone with benzene and phenol was studied for the first time by ab initio methods <2003PCA7574>. The addition to benzene had the largest calculated activation energy (15.8 kcal mol the experimental value is... 

From a more general perspective, the example at hand highlights a situation where PCM alone is unable to account fully for solvent effects on spectroscopic properties (e.g. the aN values in solution computed with PCM are 15.70, 15.75 and 15.80 G, versus experimental values of 16.58, 16.15 and 16.91 G for phenol, methanol and water respectively) this is typically related to the presence of strong, specific H-bond interactions. As shown in Figure 2.6, inclusion of specific hydrogen bond effects results in a further increase of the computed aN values, with final results close to their experimental counterparts (16.35, 16.15 and 16.51 G). 

Figure 6 Experimental values of phenol concentration vs. irradiation time. Ti02 P25 catalyst amount 0.32 g L , lamp power, 500 W. The empty symbols indicate the concentration of starting solution. The solid lines represent the Freundlich photoadsorption model [Equation (26)].

Figure 13 shows the data for the three phenolic groups of ribonuclease which ionize reversibly (Tanford etal., 1955a), based on spectrophotometric titration curves such as Fig. 11. A straight-line plot is obtained, in agreement with Eq. (14). The values of w are 0.112, 0.093, and 0.061, respectively, at ionic strengths 0.01, 0.03, and 0.15. (The salt used to produce the ionic strength was KCl, and there is evidence that neither K" nor CF is bound to an appreciable extent. The use of Zn as abscissa is therefore presumably acceptable.) Comparison with the calculated values of Table III shows that the experimental values are lower than predicted by about 20%. Such a deviation must be considered almost within the error of calculation. [If the radius of the hydrodynamically equivalent sphere (19 A) had been used as the basis of calculation, the calculated values of w would have become 0.119, 0.096, and 0.066, respectively.]...

None of the experimental values can be considered reliable Phenolic ... 

The experimental values of the degree of dissociation of carboxyl, amino, and phenolic groups, which were used to obtain the data of Figs. 17 and 21 were of course based on the notion that all titratable groups are accessible... 

TABLE 2. Rotational constants (in MHz) of phenol in its electronic ground state. The values in parentheses are the deviation from the experimental values in percent... 

At the B3LYP/6-31 l-b- -G(d,p) -b ZPE level of theory, the local PAs of phenol at different sites are evaluated in kJmoL as follows 820 for para-C, 809 for ortho-C2, 757 for meta-Cs, 699 for ipso-C and 743 for oxygen . The coupled-cluster CCSD(T) approach in conjunction with the 6-311-1— -G(d,p) basis set yields a PA(C4) of 819 kJmol . When using an appropriate basis set, the calculated PAs thus compare reasonably well with the experimental value quoted above. 

A convenient measure of the gas-phase acidity is the proton affinity (PA) of the anion, or conversely, the deprotonation energy (DPE) of the acid. For the parent phenol, the experimental value can be deduced from equation 28 for the PA of phenolate,... 

From archival enthalpies of formation and of fusion, the estimated enthalpy of formation of solid 3,5-dibromotoluene is 28 9 kJ moF. This value, combined with 5 (OH/H), gives a predicted enthalpy of formation of the corresponding phenol of —175 kJ moF. A bromine atom and methyl group crowd the intervening OH, which could account for at least some of the ca 16 kJ moF difference between the predicted and experimental values, and we don t expect 2,4-dibromo-6-methylphenol to participate in intermolecular hydrogen bonding. The remainder of the difference is accounted for by the error bars. Altogether, the value is plausible. 

It is usually extremely difficult to calculate AGs of ground-state acids from first principles with uncertainty of less than several kcalmol, which translates into uncertainty of several pXa units. In the excited state an additional difficulty involves the accurate electronic description of the excited state, which makes the task of calculating the pX of a photoacid even tougher. A recent attempt to calculate the excited-state pKl of phenol resulted in a value larger by more than 4 pXa units than the experimental one (a value of pX (calc) = —0.2, compared to the experimental value of about 4). A very recent calculation of the ground-state dissociation constant of phenol resulted also in overestimation of the dissociation constant, giving 7.2 compared to the experimental value of about 10.0. ... 

The dissociation energy Do of the phenol-methanol complex (phenol as hydrogen-bond donor), calculated with MP2 and B3LYP using the rather small 6-31G(d, p) basis set, is 21.78 and 22.91 klmoL, respectively . The calculated Do shows good agreement with the experimental value (25.56 0.75 kJmoP ) . 

This relationship was then used to calculate the BDE for a-Toc, giving a value of 77.2 kcalmor, in excellent agreement with the experimental value of 77.3 kcalmoP. This empirical method does depend on the electronic effects of groups (methyls and para-ether) around the phenyl ring and provides some confirmation of the role these play in weakening the O—H bond and thus raising the antioxidant activity. In a similar manner, Jovanovic and coworkers obtained a correlation between the measured reduction potentials and the a+ constants for twenty-one substituted phenols at pH 7 (equation 59) and pH 0 (equation 60) ". ... 

Using the a values for ortho substituents given in Appendix 3, Table 10 calculate the pA values of the following (experimental values given in brackets) 2-chloro-4-nitrobenzoic acid (1.96), 2,6-dimethylpyridine (6.77), 2,4-dichloroanilinium ion (2.05) and 2,3,5-trichlorophenol (6.43). Hammett equations for the dissociation of substituted phenols, pyridinium ions, anilinium ions and benzoic acids are given in Appendix 4, Table 1. 

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