This review presents a critical assessment of the available experimental information (contained in ∼90 literature references) on thermochemistry O–H bond phenol and substituted phenols. The analysis led to set recommended values for dissociation enthalpies, which turn allowed us discuss several empirical theoretical methodologies used estimate these data.

Time-resolved photoacoustic calorimetry (TR-PAC) and quantum chemistry calculations were used to investigate the energetics of sulfur−hydrogen bonds in thiophenol four para-substituted thiophenols, 4-XC6H4SH (X = CH3, OCH3, Cl, CF3). The result obtained for PhS−H gas-phase bond dissociation enthalpy, derived from PAC experimental results solution, is 349.4 ± 4.5 kJ mol-1. This value significantly higher than recent literature values but agrees with a suggested some 20 years ago widely...

The gas-phase enthalpy of formation cubane (603.4 ± 4 kJ mol(-1)) was calculated using an explicitly correlated composite method (W1-F12). result obtained for cubane, together with the experimental value sublimation, 54.8 2.0 mol(-1), led to 548.6 4.5 mol(-1) solid-phase formation. This is only 6.8 higher than 50-year-old original calorimetric result. carbon-hydrogen bond dissociation (C-H BDE) (438.4 mol(-1)), properties relevant its determination ion thermochemistry, namely acidity (1704.6...

The demand for novel effective antioxidant-based drugs has led to the synthesis and evaluation of antioxidant potential in several molecules derived from natural compounds. In this work vitro activity an abietic acid-derived catechol (methyl 11,12-dihydroxyabietate-8,11,13-trien-18-oate, MDTO) was evaluated. This substance, possessing important biological properties, is similar carnosic acid, a rosemary or sage leaves. Aiming understand MDTO, energetics its O−H bond, using time-resolved...

The C−H bond dissociation enthalpies (BDEs) for the five- and six-membered ring alkanes, alkenes, dienes were investigated discussed in terms of conventional strain energies (SEs). New determinations are reported cyclopentane cyclohexane by time-resolved photoacoustic calorimetry quantum chemistry methods. BDEs alkenes yielding alkyl radicals cyclopenten-4-yl cyclohexen-4-yl α-C−H BDE cyclopentene also calculated. s-homodesmotic model was used to determine SEs both parent molecules radicals....

Monte Carlo statistical mechanics simulations, density-functional theory calculations, time-resolved photoacoustic calorimetry, and isoperibol reaction-solution calorimetry experiments were carried out to investigate the solvation enthalpies solvent effects on energetics of phenol O−H bond in benzene acetonitrile. A good agreement between theoretical experimental results is obtained for The calculations also indicate that differences (PhOH) phenoxy radical (PhO•) both acetonitrile are...

Research on pharmaceutical dry powders has been increasing worldwide, along with increased therapeutic strategies for an application through the pulmonary or nasal routes. In vitro methodologies and tests that mimic respiratory environment process of inhalation itself are, thus, essential. The literature frequently reports cell-based in assays involve testing suspension. This experimental setting is not adequate, as both lung cavity are devoid abundant liquid. However, devices permit powder...

The photolysis reaction of di-tert-butylperoxide was studied in various solvents by photoacoustic calorimetry (PAC). This technique allows the determination enthalpy this homolysis reaction, which definition corresponds to O-O bond dissociation peroxide solution, DHsin(degrees)(O-O). derived value from these experiments benzene, 156.7 +/- 9.9 kJ mol(-1), is very similar a widely accepted for gas-phase enthalpy, DH(degrees)(O-O) = 159.0 2.1 mol(-1). However, when PAC-based used together with...

Aiming to improve our understanding of the stability radicals containing allylic moiety, carbon−hydrogen bond dissociation enthalpies (BDEs) in propene, isobutene, 1-butene, (E)-2-butene, 3-metylbut-1-ene, (E)-2-pentene, (E)-1,3-pentadiene, 1,4-pentadiene, cyclohexene, 1,3-cyclohexadiene, and 1,4-cyclohexadiene have been determined by quantum chemistry calculations. The BDEs also obtained time-resolved photoacoustic calorimetry. theoretical study involved a DFT method as well ab initio...

Time-resolved photoacoustic calorimetry (TR-PAC) was used to investigate the energetics of O–H bonds phenol, catechol, pyrogallol, and phloroglucinol. Values −27.1 ± 3.9, −44.1 4.4 −1.6 3.8 kJ mol−1, respectively, were obtained for solution-phase (acetonitrile) bond dissociation enthalpies last three compounds relative enthalpy in ΔDHosln(ArO–H) = DHosln(ArO–H) − DHosln(PhO–H). A value 388.7 3.7 mol−1 determined PhO–H acetonitrile. Density functional theory (MPW1PW91/aug-cc-pVDZ)...

The PhCH2−H bond dissociation enthalpy in solution was determined for the first time as 380.5 ± 5.1 kJ mol-1, from a time-resolved photoacoustic calorimetry study (TR−PAC) toluene. derived gas-phase result, 375.5 5.0 allows calculation of formation benzyl radical ΔfH° (PhCH2•, g) = 208.0 which is excellent agreement with value recently published literature, obtained experiments, and demonstrates accuracy TR−PAC tool organic energetics. A detailed discussion methods assumptions used to derive...

The gas-phase C−H bond dissociation enthalpy (BDE) in 1,3-cyclopentadiene has been determined by time-resolved photoacoustic calorimetry (TR-PAC) as 358 ± 7 kJ mol-1. Theoretical results from ab initio complete basis-set approaches, including the composite CBS-Q and CBS-QB3 procedures, extrapolated coupled-cluster calculations (CCSD(T)) are reported. CCSD(T) prediction for BDE of (353.3 mol-1) is good agreement with TR-PAC result. On basis experimental theoretical values obtained, we...

The influence of common tea preparation procedures (temperature, infusion time, consumption time interval and bag/loose-leaf) the type water used, on total phenolic content (TPC), radical scavenging activity α-glucosidase inhibitory were assessed. Higher TPC antioxidant obtained when using lower mineralized waters. Tea bags also evidenced higher than loose-leaf samples. Under same conditions (90 ºC five minutes time) green contains almost twice quantity polyphenols free ability black tea. In...

Gas-phase C−H bond dissociation enthalpies (BDEs) in norbornane were determined by quantum chemistry calculations and the C2−H BDE was experimentally obtained for first time time-resolved photoacoustic calorimetry. CBS-Q CBS-QB3 methods used to derive values DH°(C1−H) = 449 kJ mol-1, DH°(C7−H) 439 DH°(C2−H) 413 mol-1. The experimental result 414.6 ± 5.4 mol-1 is excellent agreement with theoretical value. trend > discussed.

Abstract Solvent effects are responsible for the difference between gas- and solution-phase bond-dissociation enthalpies (BDEs), thus crucial understanding reactivity in solution. While solvation can be negligible (e.g., reactions involving carbon-centered radicals), they may rather significant when oxygen-centered radicals formed). This paper reviews a number of models which have been proposed to deal with energetics radical its parent molecule. It is concluded that radical-solvent...

What is the outcome of this reaction? In acetonitrile solution, methylenic CH bond approximately 25 kJ mol−1 weaker than OH in same molecule (see picture), as demonstrated by time-resolved photoacoustic calorimetry and quantum chemical methods. However, shown electron spin resonance spectroscopy, tert-butoxy radical selectively abstracts hydrogen atom from OH group.

Abstract The hydrogen‐abstraction reaction from phenol by tert ‐butoxyl radical was used to test time‐resolved photoacoustic calorimetry (TR‐PAC) as a method obtain kinetic data. Absolute rate constants for this were determined in benzene and the 298–312 K temperature range, using temperature‐controlled calorimeter, yielding an average value of 3.5 × 10 8 M −1 s . This is good agreement with literature results obtained laser flash photolysis (LFP). Kinetic solvent effects (KSE) same also...

The energetics of tert-butoxyl radical addition reaction to norbornadiene was investigated by time-resolved photoacoustic calorimetry (TR-PAC). result, together with the C-O bond dissociation enthalpy (BDE) in product, allowed us calculate pi-bond norbornadiene. Quantum chemistry (QC) methods were also used obtain several enthalpies oxygen-centered radicals alkenes. these molecules calculated a procedure similar that case and compared pi-BDE values obtained method proposed Benson. These two...