Acids and Bases - Organic Chemistry Notes PDF

Module 2: Acids and Bases cc 1 Proton H Brønsted-Lowry Definitions (1923): An acid is a proton donor (has a tendency to lose H+ ions) acid EXTHCI H2O CI Hot A base is a proton acceptor (has a t...

Module 2: Acids and Bases cc 1 Proton H Brønsted-Lowry Definitions (1923): An acid is a proton donor (has a tendency to lose H+ ions) acid EXTHCI H2O CI Hot A base is a proton acceptor (has a tendency to gain H+ ion) Make abond Ho Ht HO H Brønsted-Lowry Acid/Base reactions are proton transfer reactions the proton transfers from the acid to the base tobond Acidbecomes replaceH the conjugate aged base H A + B A + H B Acid conj Base Base 8H Basebecomes conjugate acid Brønsted acids must have: Brønsted bases must have: A proton A pair of s usually neutralchffed neutral or charge  g y Acid Strength and pKa Acid strength is the tendency of an acid to donate a proton to donateH stronger acids are likely How do we measure and compare acid strength: acidity constant, Ka HA H2O I A H30 Larger the ha strongerthe H30ᵗ A acid ha Morethe proton HA isdonated However, organic acids are generally weak and have small Ka values (10–5 to 10 –50 ) – more convenient to use pKa instead w pha's PH log H30 PKa 1ogMa Pha is Ma 10 5 A STRONGER pka 5 acid Ttr via110 50 pha 50 weamer t acid  Organic Acids and Bases Functional groups are common patterns of atoms that have characteristic physical and chemical properties. A functional group will react the same way, regardless of the rest of the molecule. Below, a carboxylic acid functional group is reacting with a nitrogen base. 0 O O C + NH3 C + NH4 H 3C OH H 3C O conjugate carboxylicacid conj base acid O O C C OH + NH3 O + NH4 M c OH I R É o ÑH4 Restofmolecule Mgroup doesn't change rn Certain functional groups can act as acids and/or bases.  Organic Acids and Bases Acidic functional groups: Carboxylic acids (pKa ~5) Alcohols (pKa ~15) Protonated Amines (pKa ~10) O H C R OH N R OH R R R Main conj acid of amines R–COOH R–CO2H strongest weakest Basic functional groups: Amines: PE N R R R N attached to C chains  Approximate pKa Values Acid pKa Conjugate Base OH O stress H 3C C OH Protonated oxygen H 3C C OH functional groups