CHEM 2222 Chapter 18 Notes
CHEM 2222 Chapter 18 Notes Chem 212 - Organic Chemistry II
Popular in Organic Chemistry II
Popular in Chemistry
Chem 212 - Organic Chemistry II
verified elite notetaker
This 28 page Class Notes was uploaded by annafen on Sunday May 29, 2016. The Class Notes belongs to Chem 212 - Organic Chemistry II at Vanderbilt University taught by Dr. Alissa Hare in Spring 2016. Since its upload, it has received 6 views. For similar materials see Organic Chemistry II in Chemistry at Vanderbilt University.
Reviews for CHEM 2222 Chapter 18 Notes
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 05/29/16
18.1 Carboxylic Acid Nomenclature Systematic Nomenclature of Carboxylic Acids • Longest continuous chain that contains the carboxylic acid is the parent. Replace the –e with –oic acid • Carboxylic carbon is numbered 1 and substituents located by number and listed alphabetically • Double bonds change the ending to –enoic acid with location for the double bond numerically. • Carboxyl group attached to a ring – parent ring name is given plus carboxylic acid • Two carboxyl groups use suf– fixioic acid. 1 Common Names for Carboxylic Acids 2 Common Names for Carboxylic Acids 3 18.2 Structure and Bonding Structure and Bonding • The pi orbitals extend from one oxygen to the other • Can draw this as resonance 4 18.3 Physical Properties Physical Properties • Boiling point is increased due to the hydrogen bonding ability and dipole moment • Carboxylic acids from a hydrogen bonded dimer - there is both a hydrogen bond donor and acceptor in the molecule 5 18.4 Acidity of Carboxylic Acids Acidity of Carboxylic Acids • Carboxylic acids have pK valuas around 5 • The conjugate base of carboxylic acids are more stable than that of alcohols • Stabilized bases are weak bases so the conjugate acid is a strong acid 6 Bond Distances and Delocalization • The greater acidity of carboxylic acids is attributed to greater stabilization of carboxylate ion by • Inductive effect of the C=O group • Resonance stabilization of the carboxylate ion • The two C-O bond distances are equal in acetate anion supporting the electron delocalization 7 Acidity Review 8 pH and pK a • Henderson–Hasselbalch equation relates pK and pH a • When [conjugate base] = [acid], pH =pKa 9 18.5 Substituents and Acid Strength Substituents • The pK ofaa carboxylic acid can be influenced by substituents on the α- carbon, largely through inductive effects. • Electron-withdrawing groups increase the acidity (lower pK ) and a electron-donating groups decrease the acidity (higher pK a). • Inductive effects work throughσ-bonds, and the effect falls off dramatically with distance 10 18.6 Ionization of Substituted Benzoic Acids Substituent Effect • Electron withdrawing groups increase the acidity due to their inductive effect but the anion can’t delocalize into the benzene ring • The effect is strongest with an electron withdrawing group ortho to the acid • Meta and para substituents have moderate effect 11 18.7 Salts of Carboxylic Acids Salts of Carboxylic Acids • Carboxylic acid are neutralized with strong bases like hydroxide which usually has a counter ion • This reaction is an acid-base reaction • Named by first specifying the metal ion and then adding the name of the acid modified by replacing -ic acid by -ate. 12 Formation of Micelles • Long chain carboxylate anions have a hydrophilic and hydrophobic sections • In aqueous solution micelles are formed comprising 50-100 individual molecules in which the hydrophobic ends aggregate • 13 18.8 Dicarboxylic Acids Acidity of Dicarboxylic Acids • There are two ionization constants, K and 1 . The s2cond ionization has a higher pKa (is less acidic) • The inductive effect of the second carboxyl group on the first ionization decreases with distance 14 18.10 Sources of Carboxylic Acids Synthesis of Carboxylic Acids 15 18.11 Synthesis of Carboxylic Acids Carboxylation of Grignard Reagents • Grignard reagents react with CO to2form carboxylic acids. • This is a C-C bond forming reaction and it adds a COOH to the molecule • Remember that Grignard reagents react with any acidic hydrogens and other electrophilic groups in the molecule • So be careful when you are designing a substrate or synthetic sequence 16 18.12 Synthesis of Carboxylic Acids From Nitriles to Carboxylic Acids • Using cyanide as a nucleophile to react with 1° and 2° alkyl halides to form a new C-C bond – via SN2 • This reaction adds one carbon and then the nitrile can be hydrolyzed to a carboxylic acid 17 Mechanism 18 From Nitriles to Carboxylic Acids 19 18.13 Reactions of Carboxylic Acids Carboxylic Acids as Reactants 20 18.14 Mechanism of Acid-Catalyzed Esterification Acid-Catalyzed Esterification • Fischer Esterification converts a carboxylic acid to an ester under acidic conditions • The alcohol used determines the ester formed • Base-catalyzed esterification can’t occur because O is a bad leaving group 21 Acid-Catalyzed Esterification 22 18.15 Intramolecular Ester Formation: Lactones Intramolecular Ester Formation: Lactones • Spontaneous process for 5 and 6 membered rings. • Cyclic esters are called lactones • Named by replacing the -oic acid ending of the parent acid by -olide and identifying its oxygenated carbon by number. 23 18.16 Decarboxylation of Malonic Acid and Related Compounds Decarboxylation of Malonic Acids • Decarboxylation is loss of CO fro2 a molecule • β-carboxyl carboxylic acids will decarboxylate with heat 24 18.17 Spectroscopic Analysis of Carboxylic Acids Infra Red Spectroscopy • The O-H and C-H stretching frequencies overlap to produce a broad peak • The carbonyl group gives a strong band for C=O stretching around 25 1H NMR Spectroscopy • The hydroxyl proton of a CO H group is normally the least shielded of all 2 the protons in an NMR spectrum, appearing • But it can exchange with water in solution and often isn’t detected or is a broad singlet 26 Other Spectroscopy • 1C NMR - The carbon of a CO H grou2 is in the range 160-185 ppm • UV-VIS - Carboxylic acids absorb at a wavelength of 210 nm • Mass Spectrometry - The dominant fragmentation in acid corresponds to loss of OH, then loss of CO 27