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Chapter 20
Carboxylic Acids

20-00-04UN

Title	Greek Lettering of Carboxyllic Acids
Caption	In common names, the position of substituents are named using Greek letters.
Notes	The carbonyl carbon does not get a greek letter, the carbon adjacent to it gets the letter a.
Keywords	carboxylic acids

20-00-18UN1-2

Title	Structural Features of Formic Acid
Caption	The entire molecule is approximately planar. The sp2 hybrid carbonyl carbon atom is planar, with nearly trigonal bond angles. The O-H bond also lies in this plane, eclipsed with the C=O bond.
Notes	The sp3 oxygen has a C-O-H angle of 106o.
Keywords	formic acid

20-00-19UN

Title	Resonance Structures of Formic Acid
Caption	One of the unshared electron pairs on the hydroxyl oxygen atom is delocalized into the electrophilic pi system of the carbonyl group.
Notes	The major resonance structure is neutral while the minor forms have charge separation.
Keywords	pi system

20-00-21UN

Title	Boiling Points of Carboxylic Acids
Caption	The high boiling points of carboxylic acids result from the formation of a stable, hydrogen-bonded dimer. This dimer contains an eight-membered ring joined by two hydrogen bonds, effectively doubling the molecular weight of the molecules leaving the liquid phase.
Notes	A higher temperature is needed to break the hydrogen bonds and vaporize the acid.
Keywords	dimer

20-00-23UN

Title	Acidity of Carboxylic Acids
Caption	A carboxylic acid may dissociate in water to give a proton and a carboxylate ion. The equilibrium constant Ka for this reaction is called the acid-dissociation constant.
Notes	The acid will be mostly dissociated if the pH of the solution is higher than the pKa of the acid.
Keywords	equilibrium constant, acid-dissociation constant, carboxylate ion

20-01

Title	Energy Diagram of Carboxylic Acids and Alcohols
Caption	Figure 20-1Carboxylic acids are more acidic than alcohols because carboxylate ions are more stable than the alkoxide ions.
Notes	The carboxylate ion has the negative charge delocalized over t=its two oxygens.
Keywords	carboxylate ion, alkoxide ion

20-02

Title	Acetate Ion
Caption	Figure 20-2Structure of the acetate ion. Each C-O bond has a bond order of 3/2 from one s bond and half a p bond. Each oxygen atom bears half of the negative charge.
Notes	The delocalization of the negative charge over the two oxygens makes the acetate ion more stable than an alkoxide ion.
Keywords	acetate ion, delocalization

20-02-02UN

Title	Substituent Effect on Acidity of Carboxylic Acids
Caption	The magnitude of a substituent effect depends on its distance from the carboxyl group. Substituents on a carbons are most effective in increasing the acid strength.
Notes	The farther away the substituents are from the carboxyl group the smaller their inductive effect.
Keywords	acid strength, inductive effect

20-02-06UN

Title	Deprotonation of Carboxylic Acids
Caption	A strong base can completely deprotonate a carboxylic acid. The products are a carboxylate ion, the cation remaining from the base, and water. The combination of a carboxylate ion and a cation is a salt of a carboxylic acid.
Notes	Sodium hydroxide is commonly used to deprotonate carboxylic acids.
Keywords	carboxylate ion, salt of a carboxylic acid

20-02-08UN

Title	Protonation of a Salt of a Carboxylic Acid
Caption	Because mineral acids are stronger than carboxylic acids, addition of a mineral acid converts a carboxylic acid salt back to the original carboxylic acid.
Notes	HCl is commonly used for protonation.
Keywords	mineral acids, protonation

20-04

Title	Hydrolysis of Fats and Oils
Caption	Figure 20-4Hydrolysis of a fat or an oil gives a mixture of the salts of straight chain fatty acids. Animal fats contain primarily saturated fatty acids, while most vegatable oils are polyunsaturated.
Notes	The hydrolysis of fat and oils produces soap.
Keywords	fatty acid, saturated fatty acid, polyunsaturated oil

20-04-04UN

Title	IR Bands of Carboxylic Acids
Caption	The most obvious feature in the IR spectrum of a carboxylic acid is the intense carbonyl stretching absorption.
Notes	Conjugation lowers the frequency of the C=O band.
Keywords	conjugation, infrared spectroscopy, spectrum, carbonyl stretching

20-05

Title	IR Spectrum of 2-Methylpropenoic acid
Caption	Figure 20-5IR Spectrum of 2-methylpropenoic acid.
Notes	There are three bands for this unsaturated carboxylic acid; the C=O stretch at 1695 cm-1, a C=C double bond stretch at 1630 cm-1, and the OH band at 2500 - 3500 cm-1.
Keywords	2-methylpropenoic acid

20-06

Title	NMR Spectrum of Butanoic Acid
Caption	Figure 20-6Proton NMR spectrum of butanoic acid.
Notes	The signal for the protons of the b methylene is a sextet, the a and g protons are triplets, and the acidic proton is a singlet at 11.2 ppm.
Keywords	butanoic acid

20-06-04UN

Title	Fragmentations of Carboxylic Acids in Mass Spectrometry
Caption	The most common fragmentation is the loss of an alkene. Another common fragmentation is the loss of an alkyl radical to give a resonance-stabilized cation with the positive charge delocalized over an allylic system and two oxygen atoms.
Notes	In the McLafferty rearrangement there is a concerted transfer of a proton from the gamma carbon to the carboxyl oxygen with the breaking of the b,g C-C bond.
Keywords	McLafferty rearrangement, mass spectrometry, fragmentation

20-07

Title	Mass Spectrum of Pentanoic Acid
Caption	Figure 20-7The mass spectrum of pentanoic acid shows a weak parent peak, a base peak from the McLafferty rearrangement, and another strong peak from loss of an ethyl radical.
Notes	The base peak is the tallest peak of the spectrum and it is assigned a 100% abundance.
Keywords	parent peak, base peak

20-07-16UN

Title	Nucleophilic Acyl Substitution
Caption	Ketones and aldehydes commonly react by nucleophilic addition to the carbonyl group, but carboxylic acids more commonly react by nucleophilic acyl substitution, where one nucleophile replaces another on the acyl (C=O) carbon atom.
Notes	Derivatives of carboxylic acids include acyl halides, anhydrides, esters, and amides.
Keywords	acyl halides, anhydrides, esters, amides, acyl substitution

20-07-18UN

Title	Fisher Esterification
Caption	Carboxylic acids are directly converted to ester by the Fisher esterification, an acid catalyzed nucleophilic acyl substitution by an alcohol. The net reaction is replacement if the acid -OH group by the -OR group of the alcohol.
Notes	Acidic conditions are necessary for the esterification to occur.
Keywords	esterification, nucleophilic acyl substitution

20-07-19UN

Title	Mechanism of the Fisher Esterification
Caption	The acid catalyst protonates the carbonyl group and activates it toward nucleophilic attack. Loss of a proton gives the hydrate of an ester.
Notes	Protonation is essential because the carbonyl group of a carboxylic acid is not electrophilic enough.
Keywords	catalyst, activation, hydrate of an ester

20-07-20UN

Title	Dehydration of an Ester Hydrate
Caption	Protonation of either one of the hydroxyl groups allows it to leave as water, forming a resonance-stabilized cation. Loss of a proton from the second hydroxyl group gives the ester.
Notes	The hydrate loses water easily.
Keywords	dehydration

20-07-29UN

Title	Synthesis of Acid Chlorides
Caption	The best reagent for converting carboxylic acids to acid chlorides are thionyl chloride (SOCl2) and oxalyl chloride (COCl2) because they form gaseous by-products that do not contaminate the product.
Notes	Thionyl chloride reaction produces SO2 while the oxalyl chloride reaction produces HCl, CO, and CO2 (all gaseous).
Keywords	thionyl chloride, oxalyl chloride

20-07-30UN

Title	Mechanism of Acid Chloride Formation
Caption	Either oxygen of the acid can attack the sulfur, replacing chloride by a mechanism that look's like sulfur's version of nucleophilic acyl substitution. The product is an interesting, reactive chlorosulfite anhydride.
Notes
Keywords	chlorosulfite anhydride

20-07-31UN

Title	Mechanism of Acid Chloride Formation
Caption	The reactive anhydride undergoes nucleophilic acyl substitution by chloride ion to give the acid chloride.
Notes	SO2 and a chloride ion are the by-products of the reaction.
Keywords	nucleophilic acyl substitution

20-07-33UN

Title	Esterification of an Acid Chloride
Caption	Attack of the alcohol at the electrophilic carbonyl group gives a tetrahedral intermediate. Loss of a chloride and deprotonation gives an ester.
Notes	Esterification of an acyl chloride is more efficient than the Fisher esterification.
Keywords	tetrahedral intermediate

20-07-34UN

Title	Amide Synthesis
Caption	Ammonia and amines react with acid chlorides to give amides, also through the addition-elimination mechanism of nucleophilic acyl substitution.
Notes	Two equivalents of amine are needed.
Keywords	amide

20-07-35UN

Title	Esterification Using Diazomethane
Caption	Carboxylic acid are converted to their methyl esters very simply by adding an ether solution of diazomethane.
Notes	The reaction usually produce quantitative yields of ester. The by-product of the reaction is nitrogen gas.
Keywords	diazomethane

20-07-36UN

Title	Mechanism of Diazomethane Esterification
Caption	The reaction of diazomethane probably involves transfer of the acid proton, giving a methyldiazonium salt. This diazonium salt is an excellent methylating agent, with nitrogen gas as a leaving group.
Notes	Diazomethane is explosive so it is used in small scale esterifications.
Keywords	diazomethane, diazonium salt

20-07-37UN

Title	Direct Synthesis of Amides
Caption	The initial reaction of a carboxylic acid with an amine gives an ammonium carboxylate salt. Heating this salt to well above 100oC drives off steam and forms and amide.
Notes	Amides can be synthesized directly from carboxylic acids, although the acid chloride procedure uses milder condition and often gives better yields.
Keywords	ammonium carboxylate salt

20-07-41UN

Title	Lithium Aluminum Hydride Reduction of Carboxylic Acids
Caption	Lithium aluminum hydride reduces carboxylic acids to primary alcohols.
Notes	The intermediate aldehyde reacts faster with the reducing agent than the carboxylic acid.
Keywords	lithium aluminum hydride

20-07-46UN

Title	Reduction of Acid Chlorides to Aldehydes
Caption	Lithium aluminum tri(t-butoxy) hydride, is a weaker reducing agent than lithium aluminum hydride. It reduces acid chlorides because they are strongly activated toward nucleophilic addition of a hydride ion.
Notes	Under these conditions, the aldehyde reduces more slowly, and it is easily isolated.
Keywords	lithium aluminum tri(t-butoxy) hydride

20-07-50UN

Title	Conversion of Carboxylic Acids to Ketones
Caption	A general method of making ketones involves the reaction of a carboxylic acid with two equivalents of an organolithium reagent.
Notes	The first equivalent of organolithium acts as a base, deprotonating the carboxylic acid.
Keywords	organolithium reagents

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