A Theoretical Study on C−COOH Homolytic Bond Dissociation Enthalpies

Abstract

The knowledge of C-COOH homolytic bond dissociation enthalpies (BDEs) is of great importance in understanding various chemical and biochemical processes involving the decarboxylation reaction. In the present study, the density functional theory (DFT method), B3P86/6-311++G(2df,2p)//B3LYP/6-31+G(d), is found to be reliable to predict the C-COOH BDE of various structurally unrelated carboxylic acids. The mean absolute deviation (MAD) and root-mean-square deviation (rmsd) of this optimal method are equal to 2.0 and 2.5 kcal/mol, respectively. With the authorized theoretical protocol in hand, an extensive C-COOH BDE scale containing over 100 carboxylic acids has been established. The availability of this body of data enabled a detailed investigation of remote substituent effect on four types of carboxylic acids, including para-substituted benzoic acid, beta-substituted cis-propenoic acid, beta-substituted trans-propenoic acid, and substituted propiolic acid. Also with the C-COOH BDE data obtained in this work, an excellent linear relationship has been found between the C-COOH BDE of carboxylic acids and the C-H BDE of their hydrocarbon analogues. After comparing the energy barrier of the Pd-catalyzed decarboxylation reaction (DeltaG(decarboxylation)++) with the related C-COOH BDE, a negative correlation between the DeltaG(decarboxylation)++ and the C-COOH BDE was found.

Targeted Fluorination with the Fluoride Ion by Manganese‐Catalyzed Decarboxylation

“…Molecules containing strongly electron-rich aromatic rings, which are challenging substrates for Selectfluor-based decarboxylative fluorination methods because of the competing aryl fluorination, [16d] were readily fluorinated without any ring fluorination (11)(12)(13). [20] The mildness of the fluorination conditions prompted us to test its application to fluorinating molecules with structures of biological importance (Scheme 2). Surprisingly, no epoxidation or CÀH activation products were observed with substrates containing olefinic C=C bonds (e.g., 11 and 26), despite the well-known [Mn(tmp)]Cl/PhIO catalytic system that efficiently performs these reactions.…”

Rotational and vibrational dynamics in the excited electronic state of deprotonated and protonated fluorescein studied by time-resolved photofragmentation in an ion trap

“…S3) 19,45 . Since the bond dissociation enthalpy for C-COOH of benzoic acid is ∼430 kJ/mol, 34 it is conceivable that at least two photons at 520 nm (∼230 kJ/mol) are necessary for generating the observed fragment ions. However, we assume that the contribution of multi-photon-pump + probe photodissociation to the time-resolved signal is negligible in our experiments, as the laser intensity used (0.3  μ J) is very low and pump-only excitation under these conditions leads to barely noticeable fragmentation (compared to pump-probe excitation; Fig.…”

“…S6) 45 . This is understandable upon consideration of the C-COOH bond dissociation enthalpy (∼430 kJ/mol for benzoic acid) 34 vs. the pump photon energy (425 nm; ∼280 kJ/mol). Based on the much lower fragmentation yield (compared to [FL − H] − ), we infer that this bond enthalpy is either higher for [FL + H] + or energy transfer from the excited xanthene unit to the benzoic acid ring is less efficient than for [FL − H] − .…”

A comparison of the C‒H bond dissociation enthalpies of sulfur-containing fused heterocyclic compounds to the C‒H bond dissociation enthalpies in other heterocycles

“…[20][21][22] With these optimized structures, the single-point energies of all the heterocyclic molecules and radicals were calculated using 13 DFT methods involving BMK, [23] KMLYP, [24] MPW1KCIS, [25] O3LYP, [26] PBE1PBE, [27] TPSS1KCIS, [28] M05, [29] MPWB1 K, [30] M06-L, [31,32] MPWLYP1 W, [33] WB97X, [34] B3LYP, [35,36] M06-2X, [37] using the 6-311 + + G(2df,2p) basis set. The natural bond orbital (NBO) [38] analysis was conducted at the BMK/6-31 + G(d) level.…”