Potential energy surfaces for protonation of hydrochlorofluoromethanes

Proton transfer reactions of halogenated compounds: Using gas chromatography/Fourier transform ion cyclotron resonance mass spectrometry (GC/FT-ICR MS) and ab initio calculations

“…Our calculated PAs of CH 3 Cl and for CH 2 Cl 2 are within 0.4 kcal mol −1 of reported calculated values [39][40][41][42] and within 0.1 kcal mol −1 of calculations of the latest results reported by He and Wang [49] except for a discrepancy of 2.4 kcal mol −1 for CH 2 Cl 2 between our results and a DFT calculation of the PA using the B3LYP approximation by Cacace et al [56]. We believe our calculations of PAs at the G2 and G3 levels are more accurate than the DFT calculations.…”

“…We used the standard G3 procedure [45] with the zero point energy corrected by using the HF frequency scaled by 0.8929, while Ma apparently used the MP2 frequencies scaled by 0.9661. However, our calculations (also Ma et al [39] and He and Wang's [49]) of the PAs of the chloromethanes at 298 K are significantly higher than the numbers quoted by Hunt and Andrews [57] and Holmes and Sodeau [58] who assumed a linear relationship between the frequency shift of the IR absorption (HF or D 2 O) bands for the entire chloromethane series (cold trapped in solid argon matrices with either HF, DF [57] or D 2 O [58] guest proton donor molecules) and the proton affinity (151.1 kcal mol −1 vs. 143 kcal mol −1 [57] for CH 2 Cl 2 and 157.8 kcal mol −1 vs. 133 kcal mol −1 [57] for CHCl 3 ). Hunt and Andrews' estimate of the PA of CCl 4 as 130 kcal mol −1 is significantly lower than the G3 value of 167.2 kcal mol −1 calculated by Ma et al and also our PA estimate based on Hess law principles.…”

“…The dissociation of protonated chloroform to give CHCl 2 + + HCl is exoergic (at 360 K) by approximately −0.6 kcal mol −1 ; this G value is estimated by using a H value of approximately 6.0 kcal mol −1 from reference [49] and the entropy estimate of 18.2 cal mol −1 K −1 (based on the present G3 calculations for protonated chloroform, CHCl 2 + , and HCl). Also, to calculate the G value for the reaction of chloroform with hydronium ion (discussed above) we used the NIST data [51] (i.e., entropy and PA for water, and entropy for hydronium which was approximated to its isoelectronic analogue (ammonia)).…”

“…The examination by us of the frequencies of the 5 and IR absorption bands of HF [57] and reported frequency shifts of the D 2 O absorption band [58] vs. the available G3 calculated PA values (from this work and Refs. [39,49]) for CH 2 Cl 2 , CHCl 3 , and CCl 4 (i.e., excluding the CH 3 Cl) showed excellent linear coefficient of > 0.9 for the frequency shift as a function of PA (the linear coefficient is drastically reduced by including CH 3 Cl). Hunt and Andrews ignored the possibility of bidentate hydrogen bonding of the H atom in HF by 2 chlorine atoms in the chloromethanes containing 2, 3, or 4 chlorine substituents in their PA estimation based on IR frequency shifts.…”

“…We believe our calculations of PAs at the G2 and G3 levels are more accurate than the DFT calculations. He and Wang's [49] calculations of the PAs of CH 3 Cl, CH 2 Cl 2 , and CHCl 3 are, like Ma's [39], at the G3 level, except that the geometries were optimized using the B3LYP/6-31G(2df,p) functional and basis set and the zero point energy was obtained from the corresponding frequencies scaled by 0.9854. We used the standard G3 procedure [45] with the zero point energy corrected by using the HF frequency scaled by 0.8929, while Ma apparently used the MP2 frequencies scaled by 0.9661.…”