Acidities of carbon acids. V. Correlation of acidities in dimethyl sulfoxide with gas-phase acidities

Abstract

tures of the conjugated diene units (Si.3 E 1.44 eV). The observed positions of the first two bands in the spectrum of 2 are therefore in excellent agreement with the predictions of the simple SR method.The zero-order SR method also predicts the position of Consecutive 3,5 Shifts in Pyridine 1-Oxide Rearrangements. One-Step Furopyridine SynthesisSir:When the 3-and 5-positions are blocked in a pyridine 1oxide, reaction with benzyne gives, under conditions of kinetic control, products resulting from 1,3-and/or 1,5-sigmatropic shifts in the original 1,2-dihydropyridine 1,3-cycloadduct.' With 3,5-dihalogenated pyridine 1 -oxides (1) elimination of hydrogen halide from the 1,5-sigmatropic shift product leads to benzofuro[ 3,2-b]pyridines in good yield.' Furopyridines are of interest since perhydro derivatives occur in the alkaloids febrifugine and jervine2 and furo [2,3-b]quinolines are present in dictamnine and related alkaloid^.^ Little work has been carried out on the synthesis Communications to the Editor

Strain‐Modulated Reactivity: An Acidic Silane

“…There is an empirical linear dependence between gas‐phase and solution p K a values within the same class of acids, [35, 37, 38] which is possible due to the fact that the free energy difference between an acid and a base is attenuated by differential solvation effects that are specific for the acid class, electric charge and solvent. Such correlations have been documented for phenols, [39] alcohols, [38, 40] amines, [41] thiols, [41] and CH‐acids [42, 43] . In this way, the gas‐phase p K a of 177.7 calculated for 2 can be compared to the gas‐phase p K a of other cationic silanes described by Krempner and co‐workers (Figure 1 B), [12] which we calculate as being 205.5 for M=K and 197.8 for M=Li (Section S5.1.4).…”

“…Such correlations have been documented for phenols, [39] alcohols, [38,40] amines, [41] thiols, [41] and CH-acids. [42,43] In this way,t he gasphase pK a of 177.7 calculated for 2 can be compared to the gas-phase pK a of other cationic silanes described by Krempner and co-workers (Figure 1B), [12] which we calculate as being 205.5 for M = Kand 197.8 for M = Li (Section S5.1.4). Knowing that pK a DMSO of the latter two silanes is 22.3 and 19.8, respectively, [12] and assuming al inear correlation, one arrives to aprojected pK a DMSO of 7.3 for 2,which falls within the experimental interval of 4.7-8.1.…”

Thermodynamics of ionization of 2,4- and 2,5-dinitrophenol in dimethylsulfoxide

“…It is to be expected, therefore, that the former would be solvated by DMSO more strongly than the latter. That the delocalization of the anion confers enhanced acidity on the acid in DMSO has also been noted by Bordwell et al (13).…”

Gas phase acidities and associated equilibrium isotope effects for selected main group mono- and polyhydrides, carbon acids, and oxyacids: A G4 and W1BD study

“…Values in parentheses denote respective D acid H°( g) and D acid G°( g) . ompound location of secondary deuterium/tritium substitution is moved from the 1 0 to 2 to 3 positions on the ring (e.g., G4 K H /K D,2°o f 1.10 [1 0 ] < 1.11 [2] < 1.15 [3]). Cyclopentadiene also displays an anomalously low secondary EIE for the 1 0 position (G4 K H / K D = 1.1) relative to the 1 0 positions on methane (G4 K H / K D = 1.6; W1BD K H /K D = 1.5) and cyclopropane (G4 K H /K D = 1.4; W1BD K H /K D = 1.4), all of which are attached to a formally sp 3 hybridized carbon reaction center (but of these, only cyclopentadiene has a readily delocalizable anion upon deprotonation).…”

“…In addition to numerous works investigating gas phase acidities of isolated groups of compounds, several studies have considered more comprehensive viewpoints, often including theoretical treatments to complement and add to the experimental database and structure-property trends (see, e.g., Refs. [2][3][4][5][6][7][8][9]). …”