Question

please thoroughly explain

Phentolamine What is the most dominant species at pH 7.4? pka = a > H+ + НАС Verapamil pka = pKa = > H K H₃ C CH₃ → H CH,CO háchoenen OCH HCO OCH3 For each: Give the functional group name, hybridization and acidity (Acidic, Basic or Neutral) of the circled atoms •Give the likely conjugate acid form in water •Estimate the pka of circled atoms •Which one is the stronger base (blue circle) 121

Answer 1

OH! pka = 10 NA L imidazole, basic tert, amine, sp3, basic phenolic, sp3, acidic OH Conjugation of a conjugate acid of H2C imidalium ion нас We know when pH > pka then the functional group loses its proton. In above molecule, phenolic group has pka =9.5, and given pH=7.4. So the pH < pka and hence phenolic group is not expected to lose its proton. Thus struncture on the left (in the box) will be predominant. H3 CH3 Ether, sp3, neutral H3 CH3 CH3 H2CO OCH3 pka = 10.5 H3cO. OCH3 + H+ Hąco H2CO OCH2 CH We know when pH >pka then the functional group loses its proton. In above molecule, protonated tert. amine has pka =10.5, and given pH=7.4. So the pH <pka and hence quaternary ammnium ion group is not expected to lose its proton. Thus struncture on the left (in the box) will be predominant. Imidazole is more basic in nature because its pka is 14.9 whereas tert. amino group pka is less basic as its pka is 10.5. Imidazole can stabilize the protonated ammonium ion via resonance such is not the case in tert. amino group.