Chapter 17 Carboxylic Acids, Esters and Amides PDF

Chapter 17 Carboxylic Acids, esters and amides  Structure and Bonding Carboxylic acids, esters, and amides all contain an acyl (RCO) group bonded to a N or O atom.  Structure and Bonding The carbonyl carbon is trigonal planar, so all bond angles are 120°. Carboxyli...

Chapter 17 Carboxylic Acids, esters and amides  Structure and Bonding Carboxylic acids, esters, and amides all contain an acyl (RCO) group bonded to a N or O atom.  Structure and Bonding The carbonyl carbon is trigonal planar, so all bond angles are 120°. Carboxylic Acids  Carboxylic Acids The functional group of a carboxylic acid is a carboxyl group, which can be represented in any one of three ways.  Nomenclature IUPAC names: For an acyclic carboxylic acid, take the longest carbon chain that contains the carboxyl group as the parent alkane. Drop the final -e from the name of the parent alkane and replace it by -oic acid. Number the chain beginning with the carbon of the carboxyl group. Because the carboxyl carbon is understood to be carbon 1, there is no need to give it a number. Nomenclature A. Naming a Carboxylic Acid (RCOOH) Sample Problem 17.1 Write the IUPAC name of the following carboxylic acid Nomenclature A. Naming a Carboxylic Acid (RCOOH) Sample Problem 17.1 Find and name the longest chain containing COOH. The COOH contributes one C to the longest chain. Nomenclature A. Naming a Carboxylic Acid (RCOOH) Sample Problem 17.1 Number and name the substituents, making sure the COOH group is at C1. Answer: 4,5-dimethylhexanoic acid  Nomenclature Many simple carboxylic acids are referred to by their common names: formic acid acetic acid benzoic acid  Nomenclature For common names, use, the Greek letters alpha (a), beta (b), gamma (g), and so forth to locate substituents.  Nomenclature An -OH substituent is indicated by the prefix hydroxy-; an -NH2 substituent by the prefix amino-; a halogen will be named as halo. Name the Following Compounds  Physical Properties The carboxyl group contains three polar covalent bonds; C=O, C-O, and O-H. The polarity of these bonds determines the major physical properties of carboxylic acids.  Physical Properties Carboxylic acids have significantly higher boiling points than other types of organic compounds of comparable molecular weight. Why? Their higher boiling points are a result of their polarity and the fact that hydrogen bonding between two carboxyl groups creates a dimer that behaves as a higher-molecular-weight compound.  Physical Properties Carboxylic acids are more soluble in water than are alcohols, ethers, aldehydes, and ketones of comparable molecular weight. Why?  Fatty Acids Fatty acids: Long chain carboxylic acids derived from animal fats, vegetable oils, or phospholipids of biological membranes. More than 500 have been isolated from various cells and tissues. Most have between 12 and 20 carbons in an unbranched chain. In most unsaturated fatty acids, the cis isomer predominates; trans isomers are rare. Animal fats are rich in ___________ ___________ ____. Plant Oils are rich in ___________ ___________ ____.  Fatty Acids The Most Abundant Fatty Acids in Animal Fats, Vegetable Oils, and Biological Membranes.  Fatty Acids Unsaturated fatty acids generally have lower melting points than their saturated counterparts.  Fatty Acids Saturated fatty acids are solids at room temperature. The regular nature of their hydrocarbon chains allows them to pack together in such a way as to maximize interactions (by London dispersion forces) between their chains.  Fatty Acids unsaturated fatty acids are liquids In contrast, all at room temperature because: the cis double bonds interrupt the regular packing of their hydrocarbon chains. The Acidity of Carboxylic Acids Acidity of Carboxylic Acids  The Acidity of Carboxylic Acids 3 B. Carboxylate Anions—Salts of Carboxylic Acids The salts of carboxylic acids formed by acid-base reactions are water-soluble ionic solids. Thus, the reaction will turn a water insoluble carboxylic acid into a water-soluble carboxylic acid salt.  The Acidity of Carboxylic Acids To name the metal salts of carboxylate ions, put the three pieces below together: name of the metal cation + parent + −ate(suffix) sodium acetate potassium propanoate  How Soap Cleans? In water, soap molecules spontaneously cluster into micelles, a spherical arrangement of molecules such that their hydrophobic parts are shielded from the aqueous environment, and their hydrophilic parts are in contact with the aqueous environment.  How Soap Cleans? When soaps and dirt, such as grease, oil, and fat stains are mixed in water as in the washing machines, the nonpolar hydrocarbon inner parts of the soap micelles “dissolve” the nonpolar substances. Indeed, a new soap micelle forms.  Acidity of Carboxylic Acids When a carboxylic acid is dissolved in aqueous solution, the form of the carboxylic acid present depends on the pH of the solution in which it is dissolved. Focus on Health & Medicine  Fischer Esterification Fischer esterification is one of the most commonly used methods for the preparation of Esters. In Fischer esterification, a carboxylic acid is reacted with an alcohol in the presence of an acid catalyst, most commonly concentrated sulfuric acid. Fischer esterification is reversible. It can be derived in either direction by the choice of experimental conditions (Le Chatelier’s principle). Explain how…..  Fischer Esterification In Fischer esterification, the alcohol adds to the carbonyl group of the carboxylic acid to form a tetrahedral carbonyl addition intermediate. The intermediate then loses H2O to give an ester. Carboxyl derivatives: Esters and Amides The Conversion of Carboxylic Acids to Esters and Amides All acyl compounds undergo a common reaction type —substitution. Access the text alternative for slide images.  Carboxyl Derivatives Three classes of compounds derived from carboxylic acids; esters, and amides. Each is related to a carboxyl group by loss of H2O from an acid reaction. The Conversion of Carboxylic Acids to Esters and Amides Carboxylic acids react with alcohols to form esters.  Ester Formation Formation of an ester is done by the Fisher esterification:  Ester Formation The Fisher esterification is an equilibrium process. According to Le Châtelier’s principle, the reaction is driven to the right by: using excess alcohol removing the water as it is formed  Esters The functional group of an ester is a carbonyl group bonded to an -OR group. R may be alkyl or aryl. The names of esters are derived from the names of the parent carboxylic acids. Name the alkyl or aryl group bonded to oxygen first, followed by the name of the acid; replace the suffix - ic acid by -ate.  Naming an Ester (RCOOR′) HOW TO Name an Ester Using the IUPAC System Example Give a IUPAC name for the ester: Step Name the R’ group bonded to the O atom as an alkyl group.  Naming an Ester (RCOOR′) HOW TO Name an Ester Using the IUPAC System Step Name the acyl group (RCO-) by: changing the “-ic acid” ending of the parent carboxylic acid to “-ate”. this becomes the second part of the name. Answer: ethyl acetate  Esters Name the following esters Draw the structure for ethyl pentanoate  Amides The functional group of an amide is a carbonyl group bonded to a nitrogen atom. Amide Formation  Amide Formation The identity of the N-compound determines the type of amide formed. Amide Formation  Naming an Amide All 1° amides are named by replacing the “-oic acid” ending of the parent carboxylic acid with “-amide”.  Naming an Amide HOW TO Name an 2° or 3° Amide Example Give a systematic name for each amide.  Naming an Amide HOW TO Name an 2° or 3° Amide Step Name the alkyl groups bonded to the N atom. Use the prefix “N-” preceding the name. N-ethyl N,N-dimethyl  Naming an Amide HOW TO Name an 2° or 3° Amide Step Name the acyl group with the suffix “-amide”. Answer: N-ethylformamide Answer: N,N-dimethylbenzamide  Amides Draw the structures for 4-ethylhexanamide and N-methylbutanamide What is the IUPAC name for the following amide  Hydrolysis of Esters and Amides 1 Esters and amides react with water to form carboxylic acids  Ester Hydrolysis An example of ester hydrolysis using an acid catalyst: The equilibrium is driven to the right by using a large amount of water.  Ester Hydrolysis An example of ester hydrolysis using an aqueous base, called saponification: This basic hydrolysis forms the carboxylate anion rather than the carboxylic acid product. Hydrolysis of Esters (base catalyzed) The acid produced by hydrolysis as in the acid-catalyzed reaction immediately reacts with the base to produce the acid salt and water. RCOOH + NaOH ------- RCOO-Na+ + H2O  Amide Hydrolysis Treatment of an amide with water in the presence of an acid catalyst (HCl) forms a carboxylic acid and an amine salt.  Amide Hydrolysis Amides are also hydrolyzed in aqueous base to form carboxylate anions and amines.  Hydrolysis of Esters and Amides Focus on Health & Medicine Triacylglycerols, common naturally occurring esters, contain three ester groups, each with a long C chain. They are lipids, water insoluble organic compounds, present in fats and oils. Hydrolysis of Esters and Amides Diets high in fat lead to obesity, so the “fake fat” olestra (Olean) was invented to replace some triacylglycerols in snack foods. The lipase enzymes cannot hydrolyze the olestra, so it passes through the body unmetabolized, providing no calories to the consumer.  Step-Growth Polymerization Step-growth polymers are formed by reaction between two molecules, each of which contains two functional groups. Each new bond is created in a separate step. Three types of step-growth polymers are made by this method: o Polyamides o Polyesters o polycarbonates  Polyamides Nylon-66 was the first purely synthetic fiber. It is synthesized from two six-carbon monomers.  Polyamides Kevlar, a polyaromatic amide (made by DuPont) is made from an aromatic dicarboxylic acid and an aromatic diamine shown below. Kelvar is much stronger than nylon-66 because the polymer contains hard –to-break benzene rings.  Polyesters The most common polyester is polyethylene terephthalate (PET) used for materials Dacron and Mylar and in making plastic soft drink bottles. PET is easily and cheaply made and forms strong stable materials.  Focus on Health & Medicine Slowly degrading polyesters are useful in making sutures. The mending tissue is held together for a length of time to heal, and then the sutures break down.