Proton affinity acetone

The reactions 2 and 3 in Table 5 set the limits for the proton affinity of phosphine. Reaction 2 shows that it is smaller than that of acetone (186 3 kcal/mol) and reaction 3 indicates that it is larger than the proton affinity of acetaldehyde (185 3 kcal/mol). Thus a value of 185 ... 

The proton affinity and acidity of uracil itself (2a) has also been the subject of computational investigation, primarily by the groups of Zeegers-Huyskens and Lee.52-57 Lee and coworkers have also conducted a series of experimental investigations that have established that uracil has four sites that are more acidic than water (Nl, N3, C5, and C6) and that 04 is 8 kcal mol-1 more basic than 0254-56 Gronert and coworkers also conducted clever mass spectrometric experiments that effected decarboxylation of orotate to form the C6-deprotonated uracil (3a), which was then used to measure the acidity of the C6-H.57,58a Gronert s calculations and experiments, later confirmed by Lee and Kurinovich using different uracil derivatives,55 established that the C6 site of uracil is quite acidic with a gas phase acidity (A//acid) of —369 kcal mol-1, this site is as acidic as acetone. Recent experiments in water, however, indicate that the C6-H of 1,3-dimethyl uracil has a pK of 34, considerably less acidic than that of acetone (pA a — 19).58b... 

Similar intense bands at approximately the same frequencies are observed when other molecules of comparable proton affinity are adsorbed in HZSM-5 e.g.water [41],dimethylether [38,40,41], acetone and various carboxylic acids [41]. Pelmenschikov et al. [42,43] pointed out that these bands are very similar to the so-called A,B,C triplet of OH bands characteristic of strong molecular hydrogen bonded complexes in liquid or solid phases. The most widely accepted explanation for the A,B,C triplet in hydrogen bonded systems is that due to Claydon and Sheppard [44], who suggested that the A,B,C triplet are in fact pseudobands caused by the superposition onto a very broad single (OH) band of two so-called Evans transmission windows caused by Fermi resonance between the (OH) mode and the first overtones of in-plane ( 2 5(OH) = 2600 cm l) and out of plane ( 2 y(OH) = 1900 cm l) bending... 

Proton affinity (PA) acetaldehyde, 123 acetone, 123 acrolein, 123 butenone, 123 dimethyl ether, 123 dimethylacrolein, 123 formaldehyde, 123 methanol, 123 methyl acetate, 123 methyl acrylate, 123 (Aj-mcthylacrolein, 123 oxetane, 123 table of, 123 tetrahydrofuran, 123 water, 123... 

Many carbonyl addition and substitution reactions are carried out under acidic conditions or in the presence of Lewis acids. Qualitatively, protonation or complexation increases the electrophilicity of the carbonyl group. The structural effects of protonation have been examined for formaldehyde, acetaldehyde, acetone, formamide, and formyl fluoride. These effects should correspond to those in more complex carbonyl compounds. Protonation results in a substantial lengthening of the C=0 bond. The calculated [B3LYP/ 6-31-H-G(phase proton affinities reflect the trend of increasing basicity with donor groups (CH3, NH2) and decreased basicity for fluorine. 

Vmin, ab initio calculations show that the equilibrium position of the proton is in the molecular plane. The 0-H hond length is 0.96A and the H-O-C angle is 116° at the HF/6-31h-G level. Thus the hond length is 0.27 A shorter and the bond angle is 13° smaller than predicted from the position of the Vmin. Still the Vmin prediction is remarkably good, particularly if we consider that the gas phase proton affinity of acetone is 196.7 kcal/mol, more than three times the magnitude of the Vmin-... 

The proton affinities of acetone, diethylketone, and benzophenone are 812.0, 836.0, and 882.3 kJ/mol, respectively. Rationalize the ranking of these values. (Data from C. Laurence and J.-F. Gal, Lewis Basicity and Affinity Scales Data and Measurement, John Wiley and Sons, United Kingdom, 2010, p. 5.)... 

Anisole (methylphenylether) can be regarded as methylated phenol and has been proposed (Kauppda 2004a) as a suitable dopant for APPI of analytes with low proton affinity (PA) values in reverse phase HPLC solvents in which benzene and toluene are unsuitable. Previously only acetone was used in these conditions but its fairly high PA (812kJ.mop ) meant that it was suitable for only analytes with even higher PA values. It was shown... 

In terms of the reactivity contribution, significant differences can occur from one type of analyte molecule to another. For example, owing to its high proton affinity (812 kJ mor ) acetone reacts via a proton transfer process as readily with H3O+(H2O) as it does with H3O+ and therefore on a quadrupole-based PTR-MS system a value of Xm 0.5 will be appropriate. However, Xm has a much lower value for toluene and benzene, since both possess a higher proton affinity than H2O but a lower proton affinity than (H20)2 (see Section 2.2.4.2 for a more detailed discussion of the reactivity of toluene with H3O+(H2O)). Note that the value of Xm may also depend on the value of E N and the temperature of the drift mbe. Toluene is a good example of this since the rate of its endothermic reaction with H30+(H20) will increase as the ion-molecule collision energy increases. An illustration of the effect of humidity is shown in Figure 4.3. 

The vertical electron affinity (EA) of acetone is given as —1.51 eV by Jordan and Burrow386. Lifshitz, Wu and Tiernan387 determine—among other compounds—the excitation function and rate constants of the slow proton transfer reactions between acclone-Ih, acetone-Dg and other ketones. The acetone enolate anion has been produced in a CO2 laser induced alkane elimination from alkoxide anions by Brauman and collaborators388-390. These show, e.g. that the methane elimination from t-butoxide anion is a stepwise process ... 

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