| Abstract | Konduktometrijski su određene konstante brzine solvolize (k) prethodno sintetiziranih supstrata, različito supstituiranih benzhidril-pentafluorfenil-etera, u 80%-tnoj vodenoj otopini etanola i 60%-tnoj vodenoj otopini acetonitrila. Konstruiran je graf ovisnosti logaritma eksperimentalno određenih konstanti brzine o parametru elektrofugalnosti, pri čemu je uočljiva značajna linearna korelacija između log k i Ef. Prema relaciji log k(25 ˚C) = sf (Nf + sf), iz dobivene jednadžbe pravca određeni su parametri nukleofugalnosti pentafluorfenolata kao izlazne skupine: Nf = −0,97 i sf = 1,29 u 80%-tnom etanolu, te Nf = −0,63 i sf = 1,34 u 60%-tnom acetonitrilu. Usporedbom ovih vrijednosti s parametrima nukleofugalnosti za 2,4-dinitrofenolat u istom otapalu, utvrđeno je da je benzhidril-pentafluorfenil-eter manje reaktivan u odnosu na benzhidril-2,4-dinitrofenil-eter, odnosno da je pentafluorfenolat lošija izlazna skupina u odnosu na 2,4-dinitrofenolat. Prema reaktivnosti u vodenoj otopini etanola, pentafluorfenolat spada u umjereno reaktivne izlazne skupine, s obzirom da se smjestio u središnji dio ljestvice nukleofugalnosti prema kojoj je tosilat najbolja izlazna skupina (Nf/sf = 7,45/0,80), a acetat najmanje reaktivna eksperimentalno određena izlazna skupina (Nf/sf = −4,73/1,18). Očekivano, pentafluorfenolat u 60%-tnom acetonitrilu pokazao je veću Nf vrijednost, te nešto veći sf parametar u odnosu na 80%-tni etanol koji predstavlja polarniju smjesu. |
| Abstract (english) | Solvolytic rate constants (k) of previously synthesized compounds, differently substitued benzhydryl pentafluorophenyl ethers, have been determined conductometrically in 80% aqueous ethanol and 60% aqueous acetonitrile. The obtained rate constants have been used for plotting log k vs. Ef value graph, which shows a significant linear correlation. The equation log k(25 ˚C) = sf (Nf + Ef) was used to calculate nucleofugality parameters, Nf and sf, of pentafluorophenolate. Calculated values are Nf/sf = −0,97/1,29 for 80% aqueous ethanol and Nf/sf = −0,63/1,34 for 60% aqueous acetonitrile. By comparing these values with nucleofugality parameters of 2,4-dinitrophenolates in 80% aqueous ethanol, it is evident that a benzhydryl pentafluorophenyl ether is less reactive than a bezhydryl 2,4-dinitrophenyl ether. In other words, 2,4-dinitrophenolate is a better leaving group than pentafluorophenolate in 80% aqueous ethanol. By observing reactivities in aqueous ethanol, pentafluorophenolate has been placed in the middle part of the nucleofugality scale, on which tosylate is the best (Nf/sf = 7,45/0,80), and acetate is least reactive experimentally determined leaving group (Nf/sf = −4,73/1,18). As expected, pentafluorophenolate in 60% aqueous acetonitrile showed a higher Nf value, and a slightly higher sf value compared to a more polar mixture, 80% aqueous ethanol. |
