pKa values and gas-phase acidities of superacid molecul
pKa values and gas-phase acidities of superacid molecul pKa values and gas-phase acidities of superacid molecul
Fluorine • Highly electronegative element • Decreases the basicity of nearby basicity centers • Has very low basicity itself • Many X-F bonds are extremely strong • C-F bond: 484 kJ/mol • High stability of fluorinated compounds • Small size • Polyfluorinated compounds have low steric strain Fluorination is intrinsically suitable for superacid design 27 Substituent properties Substituent σ F σ R σ α 0.13 -F 0.57 -0.33 -CF 3 0.46 0.09 -0.25 -SO 2 CF 3 0.18 0.83 0.26 -0.58 -CN 0.54 -0.46 • Neither –F nor –CF 3 seem particularly impressive 28 14
-F and -CF 3 vs -CN Acid X OH (DFT B3LYP/6-311+G**) Gas-phase acidity (kcal/mol) -CN -F -CF 3 325 340 330 X X X - B X H + 250 277 X X 259 290 244 X HBX 4 213 X X C X X - X X X X X X H + X 225
- Page 4 and 5: What is a superacid? • Superacidi
- Page 6 and 7: Solvent • As low basicity as poss
- Page 8 and 9: UV-Vis ΔpK a measurement Compound
- Page 10 and 11: 67 4NO 2 C 6 H 4 SO 2 NHTos 10.04 6
- Page 12 and 13: Important aspects for superacids
- Page 16 and 17: 250 256 255.5 HSbF 6 250.8 HAuF 6 2
-F <strong>and</strong> -CF 3 vs -CN<br />
Acid<br />
X OH<br />
(DFT B3LYP/6-311+G**)<br />
Gas-<strong>phase</strong> acidity (kcal/mol)<br />
-CN -F -CF 3<br />
325 340 330<br />
X<br />
X<br />
X<br />
-<br />
B X H +<br />
250<br />
277<br />
X<br />
X<br />
259<br />
290<br />
244<br />
X<br />
HBX 4<br />
213<br />
X<br />
X<br />
C X<br />
X<br />
-<br />
X<br />
X<br />
X X X<br />
X H +<br />
X<br />
225<br />
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