Chapter 14 Alcohols, Phenols, and Ethers PDF

Chapter 14 Alcohols, Phenols, and Ethers  Chapter 14 Table of Contents 14.1 Bonding Characteristics of Oxygen Atoms in Organic Compounds 14.2 Structural Characteristics of Alcohols 14.3 Nomenclature for Alcohols 14.4 Isomerism for Alcohols 14.5 Importan...

Chapter 14 Alcohols, Phenols, and Ethers  Chapter 14 Table of Contents 14.1 Bonding Characteristics of Oxygen Atoms in Organic Compounds 14.2 Structural Characteristics of Alcohols 14.3 Nomenclature for Alcohols 14.4 Isomerism for Alcohols 14.5 Important Commonly Encountered Alcohols 14.6 Physical Properties of Alchols 14.7 Preparation of Alcohols 14.8 Classification of Alchols 14.9 Chemical Reactions of Alcohols 14.10 Polymeric Alchols 14.11 Structural Characteristics of Phenols 14.12 Nomenclature for Phenols 14.13 Physical and Chemical Properties of Phenols 14.14 Occurrence of and Uses for Phenols 14.15 Structural Characteristics of Ethers 14.16 Nomenclature for Ethers 14.17 Isomerism for Ethers 14.18 Physcial and Chemical Properties of Ethers 14.19 Cyclic Ethers 14.20 Sulfur Analogs of Alcohols 14.21 Sulfur Analogs of Ethers Copyright © Cengage Learning. All rights reserved 2  Section 14.1 Bonding Characteristics of Oxygen Atoms in Organic Compounds Oxygen is a Group VIA Element – Has 6 valance electrons Two lone pairs Two bonding pairs, i.e., it can form two covalent bonds Two single or one double bond Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 3  Section 14.1 Bonding Characteristics of Oxygen Atoms in Organic Compounds Bonding in organic compounds: – Carbon forms four bonds – Hydrogen forms one bond – Oxygen forms two bonds. C H O 4 Valence Electrons 1 Valence Electron 6 Valence Electrons 4 Covalent bonds 1 Covalent bonds 2 Covalent bonds No nonbonding pairs No nonbonding pairs 2 nonbonding pairs Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 4  Section 14.2 Structural Characteristics of Alcohols Alcohol: An organic compound in which an —OH group is bonded to a saturated carbon atom. Saturated carbon atom: A carbon atom that is bonded to four other atoms. General structure: R-OH (OH is functional group) – Examples: CH3OH, C3H7OH – OH in alcohols is not ionic as in NaOH. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 5  Section 14.2 Structural Characteristics of Alcohols The Similar Shapes of Water and Methanol Alcohols may be viewed structurally as alkyl derivatives of water. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 6  Section 14.3 Nomenclature for Alcohols Common Names for Alcohols Common names for Alcohols (C1-C4 alkyl groups). − Rule 1: Name all of the carbon atoms of the molecule as a single alkyl group. − Example: Methyl (C1), Ethyl (C2), propyl (C3) butyl (C4) − Rule 2: Add the word alcohol, separating the worlds with a space. − Examples: CH3 OH CH3 CH2 OH CH3 CH2 CH2 OH Methyl alcohol Ethyl alcohol Propyl alcohol OH CH3 CH OH CH3 Isopropyl alcohol Cyclobutyl alcohol Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 7  Section 14.3 Nomenclature for Alcohols IUPAC Rules for Naming Alcohols Rule 1: Name the longest carbon chain to which the hydroxyl group is attached. The chain name is obtained by dropping the final “-e” from the alkane name and adding the suffix “-ol.” Rule 2: Number the chain starting at the end nearest the hydroxyl group, and use the appropriate number to indicate the position of the —OH group. (In numbering of the longest carbon chain, the hydroxyl group has priority over double and triple bonds, as well as over alkyl, cycloalkyl, and halogen substituents.) Rule 3: Name and locate any other substituents present. Rule 4: In alcohols where the —OH group is attached to a carbon atom in a ring, the hydroxyl group is assumed to be on carbon 1. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 8  Section 14.3 Nomenclature for Alcohols Alcohols with More Than One Hydroxyl Group Named with slight modification of IUPAC rules. Alcohol with two hydroxyl groups is named as a diol. Alcohol with three hydroxyl groups is named as a triol, and so on. In these names for diols, triols, and so forth, the final -e of the parent alkane name is retained for pronunciation reasons. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 9  Section 14.4 Isomerism for Alcohols Constitutional isomerism is possible for alcohols containing three or more carbon atoms. Two types of isomers – Skeletal isomers – Positional isomers Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 10  Section 14.5 Important Commonly Encountered Alcohols Methyl Alcohol (Methanol) Good fuel and used as a solvent in paints Commonly called wood alcohol – original method of its preparation was by heating wood at high temperature in the absence of air. Currently, nearly all methyl alcohol is produced via the reaction between H2 and CO. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 11  Section 14.5 Important Commonly Encountered Alcohols Methyl Alcohol (Methanol) Toxic: oxidized by alcohol dehydrogenase in the body to toxic formaldehyde and formic acid – toxic to the eye and can cause blindness and/or optic nerve damage. – Treated with ethanol: Ethanol stops oxidation of methanol by competing with alcohol dehydrogenase enzyme Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 12  Section 14.5 Important Commonly Encountered Alcohols Ethyl Alcohol (Ethanol) Also called grain alcohol as obtained by fermentation of grains like corn, rice and barley. Prepared by yeast fermentation of plant sugars by yeast – Maximum concentration of ethanol: 18% (yeast enzymes are inactivated at higher concentration of alcohol) – Excellent solvent and a fuel Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 13  Section 14.5 Important Commonly Encountered Alcohols Ethyl Alcohol (Ethanol) – Distributed as denatured Alcohol: Toxic substances such as methanol are added to prevent human consumption – Oxidized by body to acetaldehyde – toxic and causes hangover effects of alcohol – Typical fatal doses for adults are about 100 mL for methanol and about 200 mL for ethanol, although smaller doses of methanol may damage the optic nerve. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 14  Section 14.5 Important Commonly Encountered Alcohols Ethyl Alcohol (Ethanol) Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 15  Section 14.5 Important Commonly Encountered Alcohols Ethyl Alcohol (Ethanol) – Oxidized by body to acetaldehyde – toxic and causes hangover effects of alcohol – Consumption of alcohol during pregnancy can cause birth defects and fetal alcohol syndrome – Also know to cause liver damage, loss of memory and alcoholism (addiction to alcohol) Proof is twice the percentage of alcohol. This system dates back to the seventeenth century and is based on the fact that a 50% (v/v) alcohol–water mixture will burn. Its flammability was proof that a liquor had not been watered down. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 16  Section 14.5 Important Commonly Encountered Alcohols Isopropyl Alcohol (2-Propanol) Isopropyl alcohol is a three-carbon monohydroxy alcohol. A 70% isopropyl alcohol in water is marketed as rubbing alcohol (used to combat high body temperature by rubbing on the skin). Isopropyl alcohol has a bitter taste. Toxicity: Twice that of ethyl alcohol (often induces vomiting and thus doesn’t stay down long enough to be fatal). In the body it is oxidized to acetone. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 17  Section 14.5 Important Commonly Encountered Alcohols Ethylene Glycol (1,2-Ethanediol) and Propylene Glycol (1,2- Propanediol) A diol with two -OH groups attached on two adjacent carbon atoms. Colorless, odorless, miscible in water, great antifreeze, airplane deicer. Extremely toxic. Propylene glycol is nontoxic and is used in drugs as solvent. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 18  Section 14.5 Important Commonly Encountered Alcohols Ethylene Glycol (1,2-Ethanediol) and Propylene Glycol (1,2- Propanediol) Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 19  Section 14.5 Important Commonly Encountered Alcohols Glycerol (1,2,3-Propanetriol) Glycerol is a triol with three -OH groups attached on three adjacent carbon atoms. Clear thick liquid Byproduct of fat metabolism Used in skin lotions and soaps Used in shaving creams due to lubricating properties Often called biological antifreeze Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 20  Section 14.6 Physical Properties of Alcohols Alcohol molecules have both polar and nonpolar character. – The hydroxyl group is polar part of the molecule – The alkyl (R) group is nonpolar part of the molcule The physical properties depend on which portion of the structure “dominates.” – Length of the nonpolar carbon chain – Number of polar hydroxyl groups Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 21  Section 14.6 Physical Properties of Alcohols Molecular Models Space-filling molecular models showing the nonpolar (green) and polar (pink) parts of methanol and 1-octanol. a. The polar hydroxyl functional group dominates the physical properties of methanol. The molecule is completely soluble in water (polar) but only partially so in hexane (nonpolar). b. Conversely, the nonpolar portion of 1-octanol dominates its physical properties; it is infinitely soluble in hexane and has limited solubility in water. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 22  Section 14.6 Physical Properties of Alcohols Boiling Points and Water Solubilities The boiling points of 1-alcohols with an —OH group on an end carbon increases as the length of the carbon chain increases. Small monohydroxy alcohols are soluble in water in all proportions. As carbon chain length increases beyond three carbons, solubility in water rapidly decreases Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 23  Section 14.6 Physical Properties of Alcohols Boiling Points and Solubilities in Water (of selected 1-alcohols) Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 24  Section 14.6 Physical Properties of Alcohols Alcohols and Hydrogen Bonding The differences in physical properties between alcohols and alkanes 1. Alcohols have higher boiling points than alkanes of similar molecular mass. 2. Alcohols have much higher solubility in water than alkanes of similar molecular mass. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 25  Section 14.6 Physical Properties of Alcohols Alcohols and Hydrogen Bonding Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 26  Section 14.7 Preparation of Alcohols Prepared by hydration of alkenes Alkenes react with water (an unsymmetrical addition agent) in the presence of sulfuric acid (the catalyst) to form an alcohol Markovnikov’s rule is used to determine the predominant alcohol product Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 27  Section 14.7 Preparation of Alcohols Addition of H2 to carbonyl ( O ). It is similar to adding H2 to a double bond. In this case one of hydrogen will be added to carbon and the other to oxygen atom of C=O. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 28  Section 14.8 Classification of Alcohols Alcohols are classified as primary (1o), secondary (2o), or tertiary (3o) alcohols Primary alcohol (1o): Hydroxyl-bearing carbon atom is bonded to only one other carbon atom. Secondary alcohol (2o): Hydroxyl bearing carbon atom is bonded to two other carbon atoms. Tertiary alcohol (3o): Hydroxyl-bearing carbon atom is bonded to three other carbon atoms. Reactions are dependent on the type of alcohol Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 29  Section 14.8 Classification of Alcohols For alcohols of similar molecular mass, 1° alcohols have higher boiling points than 2° alcohols, which in turn have higher boiling points than 3° alcohols, because of how stearic hindrance affects hydrogen bonding. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 30  Section 14.8 Classification of Alcohols Menthol is a naturally occurring terpene alcohol with a pleasant, minty odor. Its IUPAC name is 2-isopropyl-5- methylcyclohexanol. Topical application of menthol to the skin causes a refreshing, cooling sensation followed by a slight burning-and prickling sensation. Its mode of action is that of a differential anesthetic. It stimulates the receptor cells in the skin that normally respond to cold to give a sensation of coolness that is unrelated to body temperature. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 31  Section 14.9 Chemical Reactions of Alcohols Combustion Like other hydrocarbons alcohols are also flammable. The combustion products are carbon dioxide and water. 2 CH3OH + 4O2 →2CO2 + 4 H2O Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 32  Section 14.9 Chemical Reactions of Alcohols Intramolecular Alcohol Dehydration A dehydration reaction in which the components of water (-H and -OH) are removed from a single reactant Also known as an elimination reaction H2SO 4 CH3 CH CH2 CH3 CH CH2 + H2O 180oC H OH Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 33  Section 14.9 Chemical Reactions of Alcohols Intramolecular Alcohol Dehydration In an intramolecular alcohol dehydration, the components of water (-H and -OH) are removed from neighboring carbon atoms with the resultant introduction of a double bond into the molecule. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 34  Section 14.9 Chemical Reactions of Alcohols Intramolecular Alcohol Dehydration Dehydration of an alcohol can result in more than one alkene product, because hydrogen loss can occur from either of the neighboring carbon atoms. Example: Dehydration of 2-butanol produces two alkenes. Zaitsev’s rule can be used determine the dominant product. H2SO4 + + H2O OH o 180 C 2-Butanol 1-Butene 2-Butene Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 35  Section 14.9 Chemical Reactions of Alcohols Zaitsev’s Rule The major product formed in an intramolecular alcohol dehydration reaction is the alkene that has the greatest number of alkyl groups attached to the carbon atoms of the double bond. – In the following reaction, the predominant product will be 2-butene because the product has CH3 attached to each carbon atom. H 2SO4 + + H 2O OH o 180 C 2 - B u ta n ol 2 - B u te n e 1 - B u te n e ( P r e do m i na n t) Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 36  Section 14.9 Chemical Reactions of Alcohols Zaitsev’s Rule An alternative way of expressing Zaitsev’s rule is: “Hydrogen atom loss, during intramolecular alcohol dehydration to form an alkene, will occur preferentially from the carbon atom (adjacent to the hydroxyl- bearing carbon) that already has the fewest hydrogen atoms.” H 2SO4 + + H 2O OH o 180 C 2 - B u ta n ol 2 - B u te n e 1 - B u te n e ( P r e do m i na n t) Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 37  Section 14.9 Chemical Reactions of Alcohols Intermolecular Alcohol Dehydration In this reaction, two molecules of alcohol combine to form an ether (Condensation reaction) – Only true for primary alcohols and 140oC. – Secondary and tertiary alcohols always give alkene. H H H2SO4 H H + H 2O 2 H O HO 140 o C H H H H Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 38  Section 14.9 Chemical Reactions of Alcohols Intermolecular Alcohol Dehydration In this reaction, two molecules of alcohol combine to form an ether (Condensation reaction) – Only true for primary alcohols and 140oC. – Secondary and tertiary alcohols always give alkene. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 39  Section 14.9 Chemical Reactions of Alcohols Intermolecular Alcohol Dehydration In this reaction, two molecules of alcohol combine to form an ether (Condensation reaction) – Only true for primary alcohols and 140oC. – Secondary and tertiary alcohols always give alkene. The following is a summary of products obtained from alcohol dehydration reactions using H SO as a catalyst. 2 4 Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 40  Section 14.9 Chemical Reactions of Alcohols Oxidation 1. An organic oxidation is an oxide-on that increases the number of C-O bonds and/or decreases the number of C-H bonds. 2. An organic reduction is a reduction that decreases the number of C- O bonds and/or increases the number of C-H bonds. Addition of oxygen or removal of hydrogen Mild Oxidizing Agents: KMnO4, K2Cr2O7, H2CrO4 Primary and Secondary Alcohols can be oxidized by mild oxidizing agents OH KMnO4 O C R + 2H R' H R R' Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 41  Section 14.9 Chemical Reactions of Alcohols Oxidation Reactivity of 1o, 2o and 3o alcohols: OH (O) O O (O) 1-propanol propaldehyde OH propionic acid (O) O OH 2-butanol 2-butanone (O) HO No Reaction 2-methyl-2butanol Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 42  Section 14.9 Chemical Reactions of Alcohols Oxidation Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 43  Section 14.9 Chemical Reactions of Alcohols Oxidation Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 44  Section 14.9 Chemical Reactions of Alcohols Oxidation Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 45  Section 14.9 Chemical Reactions of Alcohols Halogenation Alcohols undergo halogenation reactions In this reaction a halogen atom is substituted for the hydroxyl group producing an alkyl halide. Alkyl halide production by this reaction is superior to alkyl halide production through halogenation of an alkane Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 46  Section 14.9 Chemical Reactions of Alcohols Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 47  Section 14.10 Polymeric Alcohols It is possible to synthesize polymeric alcohols with structures similar to those of substituted polyethylenes The simplest polymer is polyvinyl alcohol (PVA) –PVA is a tough, whitish polymer that can from strong films, tubes, and fibers that are highly resistant to hydrocarbon solvents –Unlike most organic polymers, PVA is water- soluble but PVA can be rendered insoluble in water, if needed, by use of chemical agents that cross-link individual polymer strands Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 48  Section 14.11 Structural Characteristics of Phenols Phenol: An organic compound in which an —OH group is attached to a carbon atom that is part of an aromatic carbon ring system Aryl group: An aromatic carbon ring system from which one hydrogen atom has been removed. General formula for an aryl alcohol: Ar-OH Substituted phenols: Aryl group substituted with other groups like CH3, NO2 , etc. OH OH H 3C phenol Cl Substituted phenol Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 49  Section 14.12 Nomenclature for Phenols Phenols: Name “Phenol” is approved by IUPAC – Assign the position of the substituent followed by its name and the word phenol – Carbon atom with -OH is always number 1 and the other substituents will be assigned minimum possible numbers with reference to hydroxyl carbon H 3C HO HO Br OH phenol 3-bromophenol 2-methylphenol Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 50  Section 14.13 Physical and Chemical Properties of Phenols Phenols : – Low-melting solids or oily liquids at room temperature. – Sparingly soluble in water – Many phenols have antiseptic and disinfectant properties. The simplest phenol: phenol – A colorless solid with a medicinal odor – Melting point: 41oC – More soluble in water than any other phenols Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 51  Section 14.13 Physical and Chemical Properties of Phenols Acidity of Phenols Unlike alcohols, phenols are weak acids in solution. As acids, phenols have Ka values of about 10-10 M. OH O- + H2O + H3O+ Phenol Phenoxide Ion Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 52  Section 14.14 Occurrence of and Uses for Phenols Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 53  Section 14.14 Occurrence of and Uses for Phenols Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 54  Section 14.14 Occurrence of and Uses for Phenols Phenols have antiseptic properties – 4-hexylresorcinol is an ingredient in many mouthwashes and throat lozenges. – o-phenylphenol and 2-benzyl-4- chlorophenol are the active ingredients in Lysol, a disinfectant. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 55  Section 14.14 Occurrence of and Uses for Phenols Phenols have antioxidant properties: BHA (butylated hydroxy anisole) and BHT (butylated hydroxy toluene) are used as food preservatives to protect it from air oxidation – Vitamin E is a phenolic antioxidant A number of phenols found in plants are used as flavoring agents and/or antibacterials. Vanillin is a phenolic which gives flavor of vanilla An antioxidant is a substance that protects other substances from being oxidized by being oxidized itself in preference to the other substances. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 56  Section 14.14 Occurrence of and Uses for Phenols Several neurotransmitters in the human body (Section 17.10), including norepinephrine, epinephrine (adrenaline), and dopamine, are catechol derivatives. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 57  Section 14.14 Occurrence of and Uses for Phenols Butylated hydroxyanisole, also known as BHA, is a synthetic phenolic antioxidant to prevent the rancidity in edible oils & fats- containing food, also a chemical preservative with the European food additive number E320. Butylated hydroxytoluene, also known as BHT, with the European food additive number E321. This ingredient is a synthetic phenolic compound that can be used as an antioxidant, preservative and stabilizer in fats and oils. It is added to preserve freshness and prevent spoilage mainly for cereals, shortenings, potato chips, margarines and nuts. Two commercial phenolic antioxidant food additives are BHA (butylated hydroxy anisole) and BHT (butylated hydroxy toluene) Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 58  Section 14.14 Occurrence of and Uses for Phenols Urushiol oily mixture of organic compounds with allergenic properties found in plants of the family Anacardiaceae, especially Toxicodendron spp. (e.g., poison oak, Chinese lacquer tree, poison ivy, poison sumac), Toxicodendron radicans, Toxicodendron rydbergii, Toxicodendron orientale. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 59  Section 14.14 Occurrence of and Uses for Phenols It is used as intensive care unit (ICU) sedation for intubated, mechanically ventilated adults and in procedures such as a colonoscopy. It provides no analgesia (pain relief). Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 60  Section 14.14 Occurrence of and Uses for Phenols Polyphenols and the French Paradox A polyphenol is a compound in which two or more phenol entities are present within the compound’s structure. The French paradox is an apparently paradoxical epidemiological observation that French people have a relatively low incidence of coronary heart disease (CHD), while having a diet relatively rich in saturated fats. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 61  Section 14.15 Structural Characteristics of Ethers Ethers: Oxygen bonded to two carbon atoms (functional group) – General formula: R-O-R – Examples: – CH3-O-CH3, CH3-O-C2H5 – Water and ether have similar structure in that two H of water are replaced by R groups in ethers Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 62  Section 14.16 Nomenclature for Ethers Name the two hydrocarbon groups attached to oxygen atom of the ether and add the word ether – The hydrocarbon groups are listed in alphabetical order – When both R groups are same than di is used with the name of R group – Examples: O O O ethyl methyl ether butyl ethyl ether dimethyl ether Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 63  Section 14.16 Nomenclature for Ethers IUPAC Nomenclature Rule 1: Select the longest carbon chain and use its name as the base name. Rule 2: Change the “-yl” ending of the other hydrocarbon group to “-oxy” to obtain the alkoxy group name − Examples: methyl becomes methoxy, ethyl becomes ethoxy, etc. Rule 3: Place the alkoxy name, with a locator number, in front of the base chain name. Examples: O O O O 2-Ethoxybutane Ethoxybenzene 1,3-dimethoxycyclohexane Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 64  Section 14.17 Isomerism for Ethers Ethers have carbon chains (two alkyl groups ) therefore the constitutional isomerism possibilities in ethers depend on: 1. The partitioning of carbon atoms between the two alkyl groups, and 2. Isomerism possibilities for the individual alkyl groups present. Isomerism is not possible for a C2 or a C3 ether C4 and C5 ethers exhibit constitutional isomers. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 65  Section 14.17 Isomerism for Ethers Functional Group Isomerism Ethers and alcohols with the same number of carbon atoms and the same degree of saturation have the same molecular formula. − For example: Dimethyl ether, and ethyl alcohol both have the molecular formula C2H6O (constitutional isomers). Functional group isomers are constitutional isomers that contain different functional groups. − C3 ether–alcohol functional group isomerism possibilities are three (see below) CH3 CH OH CH3 CH2 O CH3 CH3 CH2 CH2 OH CH3 Ethyl methyl ether Propyl alcohol Isopropyl alcohol Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 66  Section 14.18 Physical and Chemical Properties of Ethers Physical properties The boiling points of ethers are similar to those of alkanes of comparable molecular mass and are much lower than those of alcohols of comparable molecular mass. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 67  Section 14.18 Physical and Chemical Properties of Ethers Physical properties Ethers more soluble in water than alkanes of similar molar mass because ethers can hydrogen bond Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 68  Section 14.18 Physical and Chemical Properties of Ethers Physical properties Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 69  Section 14.18 Physical and Chemical Properties of Ethers The term ether Chemical properties comes from the Ethers are Flammable, e.g., Diethyl Latin aether, ether has boiling point of 35oC and which means “to therefore a flash-fire hazard. ignite.” These compounds have high vapor pressure at room temperature, which makes them very flammable. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 70  Section 14.18 Physical and Chemical Properties of Ethers Chemical properties Ethers react slowly with oxygen from the air to form unstable hydroperoxides and peroxides. Unreactive towards acids, bases and oxidizing agents (useful for organic reactions) Like alkanes, ethers also undergo halogenation reactions Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 71  Section 14.18 Physical and Chemical Properties of Ethers Chemical properties ✓ Widely used gasoline additive since the early 1980s.. ✓ MTBE is blended into gasoline to increase its octane rating and knock resistance, and reduce 2-methoxy-2-methylpropane unwanted emissions ✓ Contamination of water supplies by small amounts of MTBE from leaking gasoline tanks and from spills. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 72  Section 14.18 Physical and Chemical Properties of Ethers Ethers as General Anesthetics ✓ In 1846, the Boston dentist William Morton was the first to demonstrate publicly the use of diethyl ether as a surgical anesthetic. ✓ Diethyl ether drawbacks: (1) It causes nausea and irritation of the respiratory passages (2) it is a highly flammable substance, forming explosive mixtures with air, which can be set off by a spark Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 73  Section 14.18 Physical and Chemical Properties of Ethers Halogenated” Anesthetics With these compounds, induction of anesthesia can be achieved in less than 10 minutes with an inhaled concentration of 3% in oxygen. The only inhalation anesthetic that contains a bromine atom. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 74  Section 14.18 Physical and Chemical Properties of Ethers Halogenated” Anesthetics Second generation” of similar halogenated ethers with even better anesthetic properties. In general, these new compounds have more fluorine atoms and fewer chlorine atoms. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 75  Section 14.19 Cyclic Ethers Cyclic ethers: Contain the ether functional groups as part of a ring system (heterocyclic organic compounds). Heterocyclic organic compound: a cyclic organic compound in which one or more of the carbon atoms in the ring have been replaced with atoms of other elements. Important cyclic ethers: THF : Useful as a solvent in that it dissolves many organic compounds and yet is miscible with water. Polyhydroxy derivatives of the five-membered (furan) and six membered (pyran) carbohydrates are cyclic ether systems Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 76  Section 14.19 Cyclic Ethers Marijuana: The Most Commonly Used Illicit Drug ✓ A marijuana “high” is a Prepared from the leaves, combination of sedation, flowers, seeds, and small tranquilization, and mild stems of a hemp plant hallucination. called Cannabis sativa. ✓ THC readily penetrates the brain. The portions of the brain that involve memory and motor control contain the receptor sites where THC molecules interact. ✓ THC readily crosses the placental barrier and reaches the fetus. ✓ THC persists in the bloodstream for several days, and the products of its breakdown remain in the blood for as long as 8 days. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 77  Section 14.20 Sulfur Analogs of Alcohols R-SH ---- Thiol R-S-R ---- Thioether Lower boiling point than corresponding alcohols due to lack of hydrogen bonding Strong disagreeable odor (in the 1–3 parts per billion range) Natural gas odor is due to added thiols Contribute to the aroma of freshly brewed coffee Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 78  Section 14.20 Sulfur Analogs of Alcohols Properties of Thiols Have lower boiling points than alcohols (lack of hydrogen bonding) Have strong, disagreeable odor The familiar odor of natural gas results from the addition of a low concentration of methanethiol (CH3—SH) to the gas. The scent of skunks is due to two thiols. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 79  Section 14.20 Sulfur Analogs of Alcohols ✓ In humans, methanethiol production is often a by-product of the metabolism of asparagus. When such metabolism occurs, a very strong odor is associated with urine in as few as 15 minutes after eating asparagus. This is not a universal problem because of genetic differences in how people metabolize sulfur-containing compounds. ✓ Studies show that a strong urine odor occurs in about 40% of the population; these individuals lack the ability to convert odiferous sulfur compounds present in asparagus to odor-free sulfate. Methanethiol (methyl mercaptan)is a colorless flammable gas, with an odor often described as that of rotten cabbage. It is the substance primarily responsible for “bad breath” and the smell of flatulence. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 80  Section 14.20 Sulfur Analogs of Alcohols Thiols are named in the same way as alcohols in the IUPAC system, except that the “–ol” becomes “-thiol. ” The prefix thio- indicates the substitution of a sulfur atom for an oxygen atom. As in the case of diols and triols, the “-e” at the end of the alkane name is also retained for thiols. CH3 CH CH2 CH3 CH3 CH2 CH2 SH SH Propanethiol 2-Butanethiol A typical smell of the human armpit is a com pound that contains both an alcohol and a thiol functional group. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 81  Section 14.20 Sulfur Analogs of Alcohols Common names for thiols are based on use of the term mercaptan, the older name for thiols. The name of the alkyl group present (as a separate word) precedes the word mercaptan. CH3 CH CH2 CH3 CH3 CH2 CH2 SH SH Propanethiol 2-Butanethiol Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 82  Section 14.20 Sulfur Analogs of Alcohols Properties of Thiols Oxidation of thiols: Lead to disulfide (S-S) bond formation 2 R-SH  → R-S-S-R + 2H The above reaction is of biological importance – Disulfide bonds formed from two —SH groups aid in protein structure stabilization More reactive than ethers due to weak C-S bond Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 83  Section 14.21 Sulfur Analogs of Ethers Thioethers (or sulfides): An organic compound in which a sulfur atom is bonded to two carbon atoms by single bonds. General formula: R—S—R. Like thiols, thioethers (or sulfides) have strong characteristic odors. Thiols are more reactive than their alcohol and ether counterparts. A carbon–sulfur covalent bond is weaker than a carbon–oxygen bond. Dimethyl sulfide is a gas at room temperature and ethyl methyl sulfide is a liquid. Thiols and thioethers exhibit functional group isomerism in the same manner that alcohols and ethers. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 84  Section 14.21 Sulfur Analogs of Ethers ✓ Bacteria in the mouth interact with saliva and leftover food to produce such compounds as hydrogen sulfide, methanethiol (a thiol), and dimethyl sulfide (a thioether). ✓ These compounds, which have odors detectable in air at concentrations of parts per billion, are responsible for “morning breath.” Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 85  Section 14.21 Sulfur Analogs of Ethers Thioethers are named in the same way as ethers, with sulfide used in place of ether in common names and alkylthio used in place of alkoxy in IUPAC names. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 86  Section 14.21 Sulfur Analogs of Ethers More than one hundred sulfur-containing organic compounds are formed in garlic, and a similar number are probably produced in the less-studied onion. Many of the compounds so produced are common to both garlic and onions. Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 87  Section 14.21 Sulfur Analogs of Ethers The smell of fried onions is considered a pleasant odor by most people. Compounds contributing to the “fried onion smell” Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 88  Section 14.21 Sulfur Analogs of Ethers Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 89  Section 14.21 Sulfur Analogs of Ethers Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 90  Section 14.21 Sulfur Analogs of Ethers Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 91  Section 14.21 Sulfur Analogs of Ethers Priority Family Ending as Highest Priority Substituent Name Group 1 Carboxylic acid -oic acid carboxy 2 Anhydride anhydride - 3 Ester -oate alkoxycarbonyl 4 Acid chloride -oyl chloride chlorocarbonyl 5 Amide -amide amido 6 Nitrile -nitrile cyano 7 Aldehyde -al Oxo(formyl only the entire aldehyde group) 8 Ketone -one oxo 9 Alcohol -ol hydroxy 10 Thiol -thiol mercapto 11 Amine -amine amino 12 Alkene -ene -en 13 Alkyne -yne -yn 14 Benzene benzene Phenyl 15 Alkane -ane Alkyl 16 Ether Alkoxy Haloalkane Halo** Nitro Nitro** Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 92  Section 14.21 Sulfur Analogs of Ethers Alkyl groups Condensed Condensed Name Structural Formula Name Structural Formula butyl - CH 2 CH2 CH2 CH 3 methyl - CH 3 2-methylpropyl - CH 2 CHCH3 ethyl - CH 2 CH3 (isobutyl) CH3 propyl - CH 2 CH2 CH3 1-methylpropyl - CH CH 2 CH3 1-methylethyl - CH CH 3 (sec-butyl) (isopropyl) CH3 CH3 CH3 1,1-dimethylethyl - CCH3 (tert- butyl) CH3 Return to TOC Return to TOC Copyright © Cengage Learning. All rights reserved 93