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Carboxylic Acids, Esters, Amines, and Amides Carboxylic acids and esters are two families of organic molecules that contain a carbonyl group (C=O) singly bonded to an oxygen atom. • A carboxylic acid contains a carboxyl group (COOH). • An ester contains an alkoxy group (OR) bonded to the carbonyl carbon. 1 Carboxylic Acids, Esters, Amines, and Amides Amines and amides are nitrogen-containing organic molecules. • An amine is an organic nitrogen compound formed by replacing one or more hydrogen atoms of ammonia (NH3) with alkyl groups. • An amide is a carbonyl compound that contains a nitrogen atom bonded to the carbonyl carbon. 2 Nomenclature Naming a Carboxylic Acid (RCOOH) To name a carboxylic acid using the IUPAC system: • Find the longest chain containing the COOH group, and change the “-e” ending of the parent alkane to “-oic acid.” • Number the chain to put the COOH group at C1, but omit “1” from the name. Apply all other nomenclature rules. CH3 O CH3CHCHCH2CH2C OH 5 4 CH3 1 hexane hexanoic acid Answer: 4,5-dimethylhexanoic acid 3 Nomenclature Naming a Carboxylic Acid (RCOOH) • Many simple carboxylic acids are referred to by their common names. A common name uses the suffix -ic acid. formic acid acetic acid benzoic acid 4 Nomenclature Naming an Ester (RCOOR’) To name an ester using the IUPAC system: • Name the R' group bonded to the oxygen atom as an alkyl group. • Name the RCO– group by changing the “-ic acid” ending of the parent carboxylic acid to the suffix “-ate.” 5 Nomenclature Naming an Ester (RCOOR′) Sample Problem 13.2 Give the IUPAC name for the following ester: O CH3CH2CH2 C OCH3 Step [1] Name the R’ group bonded to the O atom as an alkyl group. O CH3CH2CH2 C OCH3 methyl group 6 Nomenclature Naming an Ester (RCOOR′) Sample Problem 13.2 Step [2] 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. O CH3CH2CH2 C OCH3 Answer: methyl butanoate derived from butanoic acid butanoate 7 Physical Properties of Carboxylic Acids and Esters • Carboxylic acids and esters are polar compounds. • Only carboxylic acids can undergo intermolecular hydrogen bonding. 8 Physical Properties Carboxylic acids also have higher boiling points than esters because esters are incapable of intermolecular hydrogen bonding. methyl acetate propanoic acid Increasing boiling point 9 Physical Properties Carboxylic acids have higher boiling points than similar alcohols because there are more hydrogen bonding interactions possible than alcohols. Increasing boiling point 10 Interesting Carboxylic Acids • Simple carboxylic acids have foul or biting odors. • Formic acid (HCO2H) is responsible for the sting of some types of ants. • Acetic acid (CH3CO2H) is the sour-tasting component of vinegar; it can be made by air oxidation of ethanol when wine “goes bad.” 11 Focus On Health & Medicine Skin Care Products • Several skin care products purported to smooth fine lines contain a-hydroxy acids. • General structure of an a-hydroxy acid: • These acids work by removing the outer, older layer of skin cells, revealing the healthier looking, new cells underneath. 12 Focus On Health & Medicine Aspirin and Anti-Inflammatory Agents • Common pain relievers that are also antiinflammatory agents contain a carboxyl group: aspirin ibuprofen 13 Interesting Carboxylic Acids Aspirin and Anti-Inflammatory Agents • Pain relievers work because they block the synthesis of prostaglandins, compounds responsible for pain responses in the body. 14 The Acidity of Carboxylic Acids • Carboxylic acids are proton (H+) donors: • They are weak acids compared to inorganic acids like HCl or H2SO4. • Only a small percentage of a carboxylic acid is ionized in aqueous solution. 15 The Acidity of Carboxylic Acids Reaction with Bases • Carboxylic acids react with bases such as NaOH to form water-soluble salts. • A proton is removed from acetic acid to form its conjugate base, the acetate anion, which is present in solution as its sodium salt, sodium acetate. • Hydroxide (OH−) gains a proton to form neutral H2O. 16 The Acidity of Carboxylic Acids 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. O CH3(CH2)6—C—O—H octanoic acid Water-insoluble O + Na+ −OH base CH3(CH2)6—C—O− Na+ + H—O—H sodium octanoate Water-soluble 17 The Acidity of Carboxylic Acids How Does Soap Clean Away Dirt? • Soap has been used by humankind for ~2000 years. • Soaps are salts of carboxylic acids that have many C atoms in a long hydrocarbon chain. • A soap molecule has two parts: 1. The ionic end is called the polar head. 2. The carbon chain of nonpolar C—C and C—H bonds is called the nonpolar tail. 18 The Acidity of Carboxylic Acids How Does Soap Clean Away Dirt? • Structure of a soap molecule: polar head ionic end nonpolar tail nonpolar end 19 The Acidity of Carboxylic Acids How Does Soap Clean Away Dirt? • In water, soap forms micelles, spherical droplets with the ionic heads on the surface and the nonpolar tails packed together in the interior. 20 The Acidity of Carboxylic Acids How Does Soap Clean Away Dirt? • Nonpolar hydrocarbon tails trap nonpolar material like grease and oil. • The polar head remains on the surface, sealing off the grease and oil, and washing away in the presence of water. 21 Reactions Involving Carboxylic Acids and Esters • Carboxylic acids and esters undergo a common type of reaction—substitution. 22 Reactions Involving Carboxylic Acids and Esters Ester Formation • Carboxylic acids react with alcohols to form esters. • Here, the OR′ group replaces the OH group. 23 Reactions Involving Carboxylic Acids and Esters Ester Formation • Formation of an ester is done by the Fisher esterification: 24 Reactions Involving Carboxylic Acids and Esters Ester Hydrolysis • Treatment of an ester (RCOOR') with water in the presence of an acid catalyst forms a carboxylic acid (RCOOH) and a molecule of alcohol (R'OH). • Here, the OH group replaces the OR′ group. 25 Reactions Involving Carboxylic Acids and Esters Ester Hydrolysis • This reaction is a hydrolysis, since bonds are cleaved by reaction with water. 26 Focus on Health & Medicine Olestra, a Synthetic Fat • 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. 27 Focus on Health & Medicine Olestra, a Synthetic Fat • Animals store energy in the form of triacylglycerols. • Using enzymes called lipases, the three ester bonds are hydrolyzed when the triacylglycerol is metabolized. • 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. 28 Focus on Health & Medicine Olestra, a Synthetic Fat • Hydrolysis of a triacylglycerol by lipase: O O CH2O CH O C R O C R’ C + HO C R O CH OH + HO C lipase O CH2O H2O CH2OH R’’ O CH2OH glycerol The 3 bonds that break are drawn in red. R’ + HO C R’’ 3 long-chain carboxylic acids 29 Focus on Health & Medicine Structure of Olestra 30 Amines Structure and Classification • Amines are organic nitrogen compounds, formed by replacing one or more hydrogen atoms of ammonia (NH3) with alkyl groups. • Amines are classified by the number of alkyl groups bonded to the N atom. • A primary (1o) amine contains 1 C—N bond, and has the general structure RNH2. 31 Amines Structure and Classification • A secondary (2o) amine contains 2 C—N bonds, and has the general structure R2NH. • A tertiary (3o) amine has 3 C—N bonds, and has the general structure R3N. • The 1o, 2o, and 3o amine N atom has a lone pair of e−, which is omitted in condensed structures. 32 Amines Structure and Classification • The amine N has a trigonal pyramidal shape, with bond angles of ~109.5o. 33 Amines Structure and Classification • The amine N atom can also be part of a ring. • Morphine and atropine each contains a nitrogen atom in a ring. • They are alkaloids—naturally occurring amines derived from plant sources. 34 Nomenclature Amines • To name a primary (1o) amine, name the alkyl group bonded to the nitrogen atom and add the suffix “-amine.” • For 2o and 3o amines with different alkyl groups, alphabetize the names of the alkyl groups. • 2o and 3o amines with identical alkyl groups are named using the prefix “di-” or “tri-”: 35 Nomenclature Amines Sample Problem 13.8 Name each amine. a. For a 1°amine, name the alkyl group and add the suffix -amine. Answer: pentylamine 36 Nomenclature Secondary and Tertiary Amines Sample Problem 13.8 b. For a 2°amine, name each alkyl group, alphabetize the names, and add the suffix -amine. Answer: ethylmethylamine 37 Nomenclature Aromatic Amines • Amines with the N directly bonded to a benzene ring are named as derivatives of aniline. • Use the prefix N- before any alkyl group bonded to the amine nitrogen. 38 Physical Properties • Many low molecular weight amines have very foul odors like rotting fish, urine, and bad breath. • Amines are polar molecules, containing either polar C—N or polar H—N bonds. • 1o and 2o amines can have intermolecular hydrogen bonding: 39 Physical Properties • 1o and 2o amines have higher boiling points than compounds that do not have intermolecular hydrogen bonding. CH3CH2OCH2CH3 diethyl ether CH3CH2CH2CH2NH2 butylamine bp = 38 oC bp = 78 oC Increasing boiling point 40 Physical Properties • 1o and 2o amines have lower boiling points than alcohols, as alcohols have stronger intermolecular hydrogen bonds. CH3CH2CH2CH2NH2 butylamine CH3CH2CH2CH2OH 1-butanol bp = 78 oC bp = 117 oC Increasing boiling point 41 Physical Properties • 3o amines have lower boiling points than 1o or 2o amines of comparable size because they have no N—H bonds. Increasing boiling point 42 Amines as Bases • Amines are bases; they are proton (H+) acceptors. • This acid–base reaction occurs with 1º, 2º, and 3º amines. • Amines are weak bases compared to inorganic bases like NaOH. 43 Amines as Bases Reactions of Amines with Acids • Amines react with acids (HCl) to form watersoluble salts. base acid conjugate conjugate acid base 44 Amines as Bases Ammonium Salts • When an amine reacts with an acid, the product is an ammonium salt. • The amine forms a positively charged ammonium ion and the acid forms an anion. 45 Amines as Bases Ammonium Salts To name an ammonium salt: • Change the suffix “-amine” of the parent amine to the suffix “-ammonium.” • Add the name of the anion. Answer: triethylammonium acetate 46 Amines as Bases Ammonium Salts • A water-insoluble amine is converted to a watersoluble ammonium salt by treatment with acid. water-insoluble water-soluble 47 Focus on Health & Medicine Ammonium Salts as Useful Salts • Many amines with medicinal properties are sold as their ammonium salts, which are transported through the aqueous bloodstream. • The antihistimine Benadryl is sold as the salt diphenhydramine hydrochloride. 48 Amides Amides contain a carbonyl group bonded to a N atom. Amides are classified based on the number of C atoms bonded to the N atom. • A primary (1o) amide contains 1 C—N bond. • It is abbreviated as RCONH2. 49 Amides • A secondary (2o) amide contains two C—N bonds, and is abbreviated RCONHR′. • A tertiary (3o) amide contains three C—N bonds, and is abbreviated RCONHR′2. 50 Nomenclature Naming an Amide • All 1o amides are named by replacing the “-oic acid” ending of the parent carboxylic acid with “-amide.” O O CH3 C C NH2 derived from acetic acid acetamide NH2 derived from benzoic acid benzamide 51 Nomenclature Naming an Amide To name a 2º or 3º amide: • Name the alkyl group (or groups) bonded to the N atom of the amide. Use the prefix “N-” preceding the name of each alkyl group. • Name the RCO– group with the suffix “-amide.” 52 Nomenclature Naming an Amide Sample Problem 13.12 Name the following amide: HCONHCH2CH3 Step [1] Name the alkyl group on the N atom, and precede its name with N-. O H C NHCH2CH3 Name: N-ethyl ethyl group 53 Nomenclature Naming an Amide Sample Problem 13.12 Step [2] Name the acyl group with “-amide.” O H C NHCH2CH3 derived from formic acid formamide Answer: N-ethylformamide 54 Physical Properties 1o and 2o amides have higher boiling points than 3o amides and esters because of intermolecular hydrogen bonding. Increasing boiling point 55 Hydrolysis of Esters and Amides Amide Hydrolysis • Treatment of an amide with water in the presence of an acid catalyst (HCl) forms a carboxylic acid and an ammonium salt. 56 Hydrolysis of Esters and Amides Amide Hydrolysis • Amides are also hydrolyzed in aqueous base to form carboxylate anions and a molecule of ammonia (NH3) or amine. 57 Interesting Amines and Amides Caffeine and Nicotine • Caffeine and nicotine are widely used stimulants of the central nervous system that contain nitrogen atoms in rings. • They are alkaloids—naturally occurring amines derived from plants. 58 Focus on the Human Body Epinephrine and Related Compounds • A hormone is a compound produced by an endocrine gland, which travels through the bloodstream to a target tissue or organ. • Epinephrine (adrenaline) is a hormone made from norepinephrine, the neurotransmitter. 59 Focus on the Human Body Epinephrine and Related Compounds • Danger or emotional stress causes the formation of epinephrine. • The body will metabolize stored carbohydrates to form glucose, which is further metabolized to provide an energy boost. • The heart rate increases and lung passages are dilated. • This effect is known as a “rush of adrenaline” or “fight-or-flight” response. 60 Focus on Health & Medicine Penicillin • The antibiotic properties of penicillin were first discovered in 1928 by Sir Alexander Fleming. • Penicillin interferes with the enzyme that synthesizes bacterial cell walls, killing the bacterium. • All penicillins contain a β-lactam: 61 Focus on Health & Medicine Common Penicillin Used Today 62