714223-47-9Relevant academic research and scientific papers
Solvolytic reactivity of heptafluorobutyrates and trifluoroacetates
Denegri, Bernard,Kronja, Olga
experimental part, p. 5927 - 5933 (2009/12/26)
(Chemical Equation Presented) A series of X,Y-substituted benzhydryl heptafluorobutyrates (1-6-HFB) and trifluoroacetates (1-6-TFA) were subjected to solvolysis in various methanol/water, ethanol/water, and acetone/water mixtures at 25°C. The LFER equation log k = sf(Ef + N f) was used to derive the nucleofuge-specific parameters (N f and sf) for SN1-type reaction. In comparison with TFA, the HFB leaving group is a better nucleofuge for less than 0.5 unit of Nf. X,Y-Substituted benzhydryl trifluoroacetates solvolyze by way of SN1 reactions unless electron-withdrawing groups are attached to aromatic rings. In such cases the substrates solvolyze faster than predicted for the SN1 route because of the change in mechanism. X,Y-Substituted benzhydryl heptafluorobutyrates examined here (Ef ≥ -7.7) solvolyze according to the SN1 pathway. The almost parallel log k vs. Ef lines in various solvents for HFBs and TFAs, and the corresponding slope parameters (sf are in the range of 0.91 and 0.83), indicate early TS with moderately advanced charge separation. NBO charges of HFB and TFA anions and the affinities obtained, all calculated at the PCM-B3LYP/6-311+G(2d,p)//PCM-B3LYP/6-311+G(2d, p) level, revealed that the HFB anion slightly better delocalizes the developing negative charge than TFA, and that the affinity of the benzhydrylium ion is slightly larger toward TFA than toward the HFB anion, which is in accordance with the greater solvolytic reactivity of HFB.
Kinetics of the solvolyses of benzhydryl derivatives: Basis for the construction of a comprehensive nucleofugality scale
Denegri, Bernard,Streiter, Andre,Juric, Sandra,Ofial, Armin R.,Kronja, Olga,Mayr, Herbert
, p. 1648 - 1656 (2007/10/03)
A series of 21 benzhydrylium ions (diarylmethylium ions) are proposed as reference electrofuges for the development of a general nucleofugality scale, where nucleofugality refers to a combination of leaving group and solvent. A total of 167 solvolysis rate constants of benzhydrylium tosylates, bromides, chlorides, trifluoroacetates, 3,5-dinitrobenzoates, and 4-nitroben-zoates, two-thirds of which have been determined during this work, were subjected to a least-squares fit according to the correlation equation log k 25°C = Sf(Nf + Ef), where s f and Nf are nucleofuge-specific parameters and E f is an electrofuge-specific parameter. Although nucleofuges and electrofuges characterized in this way cover more than 12 orders of magnitude, a single set of the parameters, namely sf, Nf, and E f, is sufficient to calculate the solvolysis rate constants at 25°C with an accuracy of ± 16%. Because sf ≈ 1 for all nucleofuges, that is, leaving group/ solvent combinations, studied so far, qualitative discussions of nucleofugality can be based on Nf.
