Physical Properties of Alcohols

The lower and middle members of the series of saturated monohydric alcohols (C₁-C₁₁) are liquids whose boiling points rise as the composition becomes more complex. Higher alcohols from C₁₂ are solids. Alcohols having an iso- structure boil at a lower temperature than those having a normal structure. The lower representatives have a characteristic alcoholic odour and a burning taste, the middle representatives C₄-C₆ have an unpleasant odour, and the higher ones are odourless. The density of alcohols is less than unity, and only that of some of aromatic alcohols is higher than unity. The first three members of the saturated alcohols mix with water in all proportions, but solubility diminishes as the radical becomes more complex. Higher alcohols, like hydrocarbons are practically water insoluble.

The molecules of alcohols in solid and liquid state, like water molecules, are associated; in this case, the molecular mass of a substance considerably increases and consequently, its volatility decreases. Association is interrupted as alcohols pass over to a vapour state. Association is caused by hydrogen bonds which originate between molecules.

Chemical Properties of Alcohols

The functional group of alcohols, the hydroxyl, determines the main chemical properties of these compounds. Alcohols are characterized by great chemical activity.

Acid and basic properties. Formation of alcoxides. Alcohols are practically neutral substances: they do not change the colour of indicators and do not react with either aqueous solutions of alkalies or dilute acids. However, in certain reactions, alcohols exhibit properties of a very weak acids and bases, i.e. they are amphoteric, like water. When alkali metals act on alcohols in unhydrous medium, hydroxyl hydrogen is forced out and alkoxides are formed. Alkoxides have the nature of salts of a very weak acid with a base. The basic properties of alcohols are exhibited in their interaction with strong acids. In this case, alcohols like water yield oxonium salts.

Formation of ethers. Ethers are obtained when alkoxides react with alkyl halides.

Dehydration of alcohols. Alcohols are capable of losing water under definite conditions. Concentrated sulphuric or phosphoric acid can be used as dehydrating agent. Alcohols dehydrate when their vapours are passed over a heated solid catalyst (silica gel, aluminium oxide, etc.).

Oxidation of alcohols. Different products can be formed, depending on the nature of alcohols and reaction conditions. Primary alcohols yield at first aldehydes, and then acids having the same number of carbon atoms. Ketones are formed from secondary alcohols. Tertiary alcohols are more stable towards oxidation.

Catalytic dehydrogenation of alcohols. Alcohols can be converted into aldehydes and ketones also by dehydrogenation, i.e. by passing alcohol vapours over a heated metallic catalyst such as copper or silver at 300C0. A typical dehydrogenation reaction is the conversion of ethyl alcohol into acetaldehyde. This reaction is endothermic.

Preparation of Alcohols

Functional Group Transformation. Alcohols can be prepared by nucleophilic substitution of alkyl halides, hydrolysis of esters, reduction of carboxylic acids or esters, reduction of aldehydes or ketones, electrophilic addition of alkenes, hydroboration of alkenes, or substitution of ethers.

C–C Bond Formation. Alcohols can also be obtained from epoxides, aldehydes, ketones, esters, and acid chloride as a consequence of C–C bond formation. These reactions involve the addition of carbanion equivalents through the use of Grignard or organolithium reagents.

REVISION EXERCISES

Ex.1. Answer the following questions:

1.What are alcohols? 2. What is the general formula of alcohols? 3. What groups are alcohols classified into? 4. What does isomerism of alcohols determine? 5. What are the methods of alcohol preparation? 6. What are the physical properties of alcohols?

Ex.2. Match the words with their definitions:

1. volatility	a. the quantity per unit volume, unit area, or unit length as the mass of a substance per unit volume;
2. derivative	b. the state of looking or being like someone or something else, correspondence in appearance or superficial qualities, a point of likeness, similarity;
3. density	c. something that comes from something else, substance that is made from another substance;
4. resemblance	d. the property ofВ certain substances in very small concentrations to stimulate chemical sense receptors that sample the air or water surrounding the animal;
5. odour	e. a substance that has a bitter taste and that forms a salt when mixed with an acid; a soluble salt obtained from the ashes of plants and consisting largely of potassium or sodium carbonate; a substance (as a hydroxide or carbonate of alkali metal) having marked basic properties;
6. alkali	f. state of being readily vaporizable at a relatively low temperature;

Ex.3. Say whether the following statements are true or false:

1. Alcohols dehydrate when their vapours are passed over a heated solid catalyst. 2. The prefix cyclo- is used for alcohols with straight-chain alkyl groups. 3. Alcohols can be converted into aldehydes and ketones also by hydration. 4. The first three members of the saturated alcohols mix with water in all proportions. 5. The isomerism of alcohols is caused by the structure of the chain. 6. The lower alcohol representatives have a characteristic alcoholic odour and a burning taste.

Ex.4. Insert the necessary word:

1. Alcohols are among the most common organic compounds. 2. They are used as … and in making perfumes, are valuable intermediates in the synthesis of other compounds, and are among the most abundantly produced organic … in industry. 3. Perhaps the two best-known alcohols are … and methanol (or methyl alcohol). 4. Ethanol is used in toiletries, pharmaceuticals, and fuels, and it is used to … hospital instruments. 5. It is, moreover, the alcohol …. 6. The anesthetic ether is also made from …. 7. Methanol is used as solvent, as raw material for the manufacture of formaldehyde and special resins, in special fuels, in antifreeze, and for cleaning metals. 8. Alcohols may be classified as primary, secondary, or tertiary, according to which carbon of the alkyl group is bonded to the … group. 9. Most alcohols are colourless liquids … at room temperature. 10. Alcohols of low molecular weight are highly … in water; with increasing molecular weight, they become less soluble in water, and their boiling points, vapour pressures, densities, and viscosities increase. (solids, beverages, chemicals, ethanol(×2), sweeteners, soluble, hydroxyl, sterilize).

Ex.5. Translate the following text:

ВNomenclature

As with other types of organic compounds, alcohols are named by both formal and common systems. The most generally applicable system is that adopted at a meeting of the International Union of Pure and Applied Chemistry (IUPAC) in Paris in 1957. Using the IUPAC system, the name for an alcohol uses the -ol suffix with the name of the parent alkane, together with a number to give the location of the hydroxyl group. The rules are summarized in a three-step procedure:

Name the longest carbon chain that contains the carbon atom bearing the в?’OH group.

Drop the final -e from the alkane name, and add the suffix -ol.

Number the longest carbon chain starting at the end nearest the в?’OH group, and use the appropriate number, if necessary, to indicate the position of the в?’OH group.

Name the substituents, and give their numbers as for an alkane or alkene.

The first example below has a longest chain of six carbon atoms, so the root name is hexanol. The в?’OH group is on the third carbon atom, which is indicated by the name 3-hexanol. There is a methyl group on carbon 3 and a chlorine atom on carbon 2. The complete IUPAC name is 2-chloro-3-methyl-3-hexanol. The prefix cyclo- is used for alcohols with cyclic alkyl groups. The hydroxyl group is assumed to be on carbon 1, and the ring is numbered in the direction to give the lowest possible numbers to the other substituents, as in, for example, 2,2-dimethylcyclopentanol.

Common names. The common name of an alcohol combines the name of the alkyl group with the word alcohol. If the alkyl group is complex, the common name becomes awkward and the IUPAC name should be used. Common names often incorporate obsolete terms in the naming of the alkyl group; for example, amyl is frequently used instead of pentyl for a five-carbon chain.

 

UNIT X Phenols

Phenol like any of a family of organic compounds is characterized by a hydroxyl (в?’OH) group attached to a carbon atom that is part of an aromatic ring. Besides serving as the generic name for the entire family, the term phenol is also the specific name for its simplest member, monohydroxybenzene (C₆H₅OH), also known as benzenol, or carbolic acid.

Physical properties of phenols. Phenols are similar to alcohols but form stronger hydrogen bonds. Thus, they are more soluble in water than are alcohols and have higher boiling points. Phenols occur either as colourless liquids or white solids at room temperature and may be highly toxic and caustic. Similar to alcohols, phenols have hydroxyl groups that can participate in intermolecular hydrogen bonding; in fact, phenols tend to form stronger hydrogen bonds than alcohols. Hydrogen bonding results in higher melting points and much higher boiling points for phenols than for hydrocarbons with similar molecular weights. For example, phenol (molecular weight [MW] 94, boiling point [bp] 182 В°C [359.6 В°F]) has a boiling point more than 70 degrees higher than that of toluene (C₆H₅CH₃; MW 92, bp 111 В°C [231.8 В°F]).

Phenols are widely used in household products and as intermediates for industrial synthesis. For example, phenol itself is used (in low concentrations) as a disinfectant in household cleaners and in mouthwash. Phenol may have been the first surgical antiseptic. In 1865 the British surgeon Joseph Lister used phenol as an antiseptic to sterilize his operating field. With phenol used in this manner, the mortality rate from surgical amputations fell from 45 to 15 percent in Lister’s ward. Phenol is quite toxic, however, and concentrated solutions cause severe but painless burns of the skin and mucous membranes. Less-toxic phenols, such as n -hexylresorcinol, have supplanted phenol itself in cough drops and other antiseptic applications. Butylated hydroxytoluene (BHT) has a much lower toxicity and is a common antioxidant in foods.

In industry, phenol is used as a starting material to make plastics, explosives such as picric acid, and drugs such as aspirin. Substituted phenols are used in the dye industry to make intensely coloured azo dyes. Mixtures of phenols (especially the cresols) are used as components in wood preservatives such as cresote. Phenol, the cresols (methylphenols), and other simple alkylated phenols can be obtained from the distillation of coal tar or crude petroleum.

Natural sources of phenols

Phenols are common in nature; examples include tyrosine, one of the standard amino acids found in most proteins; epinephrine (adrenaline), a stimulant hormone produced by the adrenal medulla; serotonin, a neurotransmitter in the brain; and urushiol, an irritant secreted by poison ivy to prevent animals from eating its leaves. Many of the more complex phenols used as flavourings and aromas are obtained from essential oils of plants. For example, vanillin, the principal flavouring in vanilla, is isolated from vanilla beans, and mehyl salicytate, which has a characteristic minty taste and odour, is isolated from wintergreen. Other phenols obtained from plants include thymol, isolated from thyme, and eugenol, isolated from cloves.

REVISION EXERCISES

Ex.1. Answer the following questions:

1. What is the definition of phenols? 2. What is the common feature between phenols and alcohols? 3. What are the physical properties of phenols? 4. Where are phenols used in industry and household utilities production? 5. What are the natural sources of phenols?

Ex.2. Match the words with their definitions:

1. caustic	a. any of a large class of volatile odoriferous oils of vegetable origin that give plants their characteristic odours and often other properties from different parts of plants (flowers, leaves, or bark) by steam distillation, expression, or extraction that are usually mixtures of compounds, and that are often used in the form of essences in perfumes, flavorings, and pharmaceutical preparations;
2. dye	b. to stop from happening and existing;
3. generic	c. joined together,В especially in pairs; acting or operating as if joined;
4. essential oils	d. able to destroy or burn something by chemical action;
5. prevent	e. related or having the rank of a biological genus;
6. conjugate	f. a soluble or insoluble coloring material.

Ex.3. Say whether the following statements are true or false:

1.The ability of phenols to form strong hydrogen bonds also enhances their solubility in water. 2. Many of the more complex phenols used as flavourings. 3. Like other alcohols, phenols undergo dehydration. 4. Benzene is derived from chlorobenzene by a variety of methods. 5. Phenols are rarely used in household products and as intermediates for industrial synthesis. 6. Phenols occur either as colourless liquids or white solids at room temperature.

Ex.4. Insert the necessary word:

1.Phenols are compounds that have an OH group directly attached to an aromatic ring. 2. Therefore, the oxygen is sp3 hybridised and the aryl carbon is sp2 …. 3. Although phenols share some characteristics with alcohols, they have distinct properties and reactions that set them apart from that functional group. 4. Phenols can participate in intermolecular hydrogen … that means that they have moderate water … and have higher boiling points than aromatic compounds lacking the phenolic group. 5. Phenols are weakly …, and in aqueous solution an equilibrium exists between the phenol and the phenoxide ion. 6. When treated with a base, the phenol gets converted to the phenoxide ion. The phenoxide ion is stabilised by resonance and delocalisation of the negative charge into the ring, therefore phenoxide ions are weaker bases than alkoxide ions. 7. This means that phenols are more acidic than alcohols, but less acidic than carboxylic acids. 8. They are useful reagents in organic synthesis. 9. The ability of phenols to form strong hydrogen bonds also enhances their …in water. 10. Phenol  …to give a 9.3 percent solution in water, compared with a 3.6 percent solution for cyclohexanol in water. 11. The association between water and phenol is unusually strong; when crystalline phenol is left out in a humid environment, it picks up enough water from the air to form liquid droplets. 12. Synthesis of phenols: most of the phenol used today is produced from benzene, through either hydrolysis of chlorobenzene or oxidation of isopropylbenzene (cumene). 13. Hydrolysis of chlorobenzene (the Dow process).: benzene is easily converted to chlorobenzene by a variety of methods, one of which is the Dow process. 14. Chlorobenzene is hydrolyzed by a strong base at high … to give a phenoxide salt, which is acidified to phenol. 15. Oxidation of isopropylbenzene: benzene is converted to isopropylbenzene (cumene) by … with propylene and an acidic catalyst. 16. … yields a cumene hydroperoxide which undergoes acid-catalyzed rearrangement to phenol and acetone. 17. Although this process seems more complicated than the Dow process, it is advantageous because it produces two …  industrial products: phenol and acetone. (valuable, hybridized, temperatures, solubility×2, acidic, dissolves, charge, bonding, treatment, oxidation).

Ex.5. Read the text and summarize the chemical properties of phenols:

Nomenclature of phenols

General synthesis of phenols. To make more complicated phenolic compounds, a more general synthesis is needed. The cumene hydroperoxide reaction is fairly specific to phenol itself. The Dow process is somewhat more general, but the stringent conditions required often lead to low yields, and they may destroy any other functional groups on the molecule. A milder, more general reaction is the diazotization of an arylamine (a derivative of aniline, C6H5NH2) to give a diazonium salt, which hydrolyzes to a phenol. Most functional groups can survive this technique, as long as they are stable in the presence of dilute acid.

Reactions of phenols. Much of the chemistry of phenols is like that of alcohols. For example, phenols react with acids to give esters, and phenoxide ions (ArOв?’) can be good nucleophiles in Williamson ether synthesis.

Acidity of phenols. Although phenols are often considered simply as aromatic alcohols, they do have somewhat different properties. The most obvious difference is the enhanced acidity of phenols. Phenols are not as acidic as carboxylic acids, but they are much more acidic than aliphatic alcohols, and they are more acidic than water. Unlike simple alcohols, most phenols are completely deprotonated by sodium hydroxide (NaOH).

Oxidation. Like other alcohols, phenols undergo oxidation, but they give different types of products from those seen with aliphatic alcohols. For example, chromic acid oxidizes most phenols to conjugated 1,4-diketones called quinones. In the presence of oxygen in the air, many phenols slowly oxidize to give dark mixtures containing quinones.

Hydroquinone. 1,4-benzenediol) is a particularly easy compound to oxidize, because it has two hydroxyl groups in the proper relationship to give up hydrogen atoms to form a quinone. Hydroquinone is used in developing photographic film by reducing activated (exposed to light) silver bromide (AgBr) to black metallic silver (Ag↓). Unexposed grains of silver bromide react more slowly than the exposed grains.

ВВ ВВВВВВВВВВВВВВВВВВВВВВВВ

ВUNIT XI ETHERS

ВВ Ethers are a class of organic compounds that contains an oxygen atom connected to two alkyl or aryl groups. These groups are represented by letter "R". The general formula of ethers isВ R–O–R'. They can be classified into two varieties. If the alkyl groups are the same on both sides of the oxygen atom then it is a simple or symmetrical ether, e.g. diethyl ether, dimethyl ether etc.В Whereas if they are different the ethers are called mixed or unsymmetrical ethers, e.g. methyl ethyl ether, methyl phenyl ether, etc. There are many specific types of ethers depending on what the "R" group is.В They may be further classified as open-chain, cyclic, saturated, unsaturated, aromatic and so on.

ВВ One of the most common ethers is diethyl ether. Diethyl ether was one of the first anesthetics used in hospitals. Ethers are generally colourless, sweet-smelling liquids at room temperature. They have a low boiling point compared to water. Due to the structure of the molecule, ether is extremely flammable, which is partially why it is no longer used in medicine today.В

ВВ The simple ethers do not have 0-H bonds, and most of their reactions are limited to the substituent groups. The chemistry of ethers, therefore, is less varied than that of alcohols. This fact is turned to advantage in the widespread use of ethers as solvents for a variety of organic reactions.

ВВ Simple ethers such as methyl or ethyl ethers usually are not suitable protecting groups because they cannot be removed except under rather drastic conditions.

ВВ Unlike alcohols, ethers are not acidic and usually do not react with bases. However, exceptionally strong basic reagents, particularly certain alkali-metal alkyls, will react destructively with many ethers. Ethers can be cleaved under strongly acidic conditions by intermediate formation of dialkyloxonium salts. Hydrobromic and hydroiodic acids are especially useful for ether cleavage because both are strong acids and their anions are good nucleophiles. Tertiary alkyl ethers are very easily cleaved by acid reagents. Ethers are susceptible to attack by halogen atoms and radicals, and for this reason they are not good solvents for radical reactions. In fact, ethers are potentially hazardous chemicals, because in the presence of atmospheric oxygen radical-chain formation of peroxides occurs, and peroxides are unstable, explosion-prone compounds. This process is called autoxidation and occurs not only with ethers but with many aldehydes and hydrocarbons.

ВВ In general, ethers are low on the scale of chemical reactivity because the carbon-oxygen bond is not cleaved readily. For this reason ethers frequently are employed as inert solvents in organic synthesis. Particularly important in this connection are diethyl ether, diisopropyl ether, tetrahydrofuran, and 1,4-dioxane.

ВВ Physical properties. Ether molecules cannot form hydrogen bonds with each other, resulting in relatively low boiling points compared to those of the analogous alcohols. The difference, however, in the boiling points of ethers and their isomeric alcohols becomes lower as the carbon chains become longer, as the van der Waals interactions of the extended carbon chain dominates over the presence of hydrogen bonding.

ВВ Ethers are slightly polar. The C-O-C bond angle in the functional group is about 110В°, and the C-O dipoles do not cancel out. Ethers are more polar than alkenes but not as polar as alcohols, esters, or amides of comparable structure. However, the presence of two lone pairs of electrons on the oxygen atoms makes hydrogen bonding with water molecules possible.

ВВ Ethers containing up to 3 carbon atoms are soluble in water due to their hydrogen bond formation with water molecules. The solubility decreases with an increase in the number of carbon atoms. The relative increase in the hydrocarbon portion of the molecule decreases the tendency of H-bond formation. Ethers are appreciably soluble in organic solvents like alcohol, benzene, acetone, etc.

ВВ В Chemical reactions. Ethers are quite stable chemical compounds which do not react with bases, active metals, dilute acids, oxidizing agents and reducing agents. Generally, they are of low chemical reactivity, but they are more reactive than alkanes. Important reactions are listed below.

ВВ Acidic cleavage. Although ethers resist hydrolysis, their polar bonds are cloven by mineral acids such as hydrobromic acid and hydroiodic acid. Hydrogen chloride cleaves ethers only slowly. Methyl ethers typically form methyl halides:

ROCH₃ + HBr в†’ CH₃Br + ROH

Some ethers undergo rapid cleavage with boron tribromide (even aluminium chloride is used in some cases) to give the alkyl bromide. Depending on the substituents, some ethers can be cloven with a variety of reagents, e.g. strong base.

ВВ Peroxide formation. When stored in the presence of air or oxygen, ethers tend to form explosive peroxides, such as diethyl ether peroxide. The reaction is accelerated by light, metal catalysts, and aldehydes. In conditions likely to form peroxides, it is recommended, when an ether is used as a solvent, not to distill it to dryness, as any peroxides that may have formed, being less volatile than the original ether, will become concentrated in the last few drops of liquid.

Lewis bases. Ethers serve as Lewis bases and Bronsted bases. Strong acids protonate the oxygen to give "onium ions." For instance, diethyl ether forms a complex with boron trifluoride, i.e. diethyl etherate. Ethers also coordinate to Mg(II) center in Grignard reagents. Polyethers, including many antibiotics cryptands, and crown ethers, bind alkali metal cations.

Alpha-halogenation. This reactivity is similar to the tendency of ethers with alpha hydrogen atoms to form peroxides. Reaction with chlorine produces alpha-chloroethers.

Ether formation

Ethers can be prepared in the laboratory in several different ways.

Dehydration of alcohols. The dehydration of alcohols affords ethers at high temperature (about 125 В°C). The reaction is catalyzed by acids, usually sulfuric acid. The method is effective for generating symmetrical ethers, but not unsymmetrical ethers, since either OH can be protonated, which would give a mixture of products. Diethyl ether is produced from ethanol by this method. Cyclic ethers are readily generated in this way. В

The dehydration route often requires conditions incompatible with delicate molecules.

The Williamson ether synthesis is an organic reaction, forming an ether from an organohalide and an alcohol. This reaction was developed by Alexander Williamson in 1850. Typically it involves the reaction of an alkoxide ion with a primary alkyl halide via an S_N2 reaction.

ВВ The Williamson reaction is of broad scope, it is widely used in both laboratory and industrial synthesis, and remains the simplest and most popular method of preparing ethers. Both symmetrical and asymmetrical ethers are easily prepared. The intramolecular reaction of halohydrins in particular, gives epoxides.

ВВ In the case of asymmetrical ethers there are two possibilities for the choice of reactants, and one is usually preferable either on the basis of availability or reactivity. The Williamson reaction is also frequently used to prepare an ether indirectly from two alcohols. One of the alcohols is first converted to a leaving group (usually to sylate), then the two are reacted together.

ВВ A typical Williamson reaction is conducted at 50–100В°C and is complete in 1–8 hours. Often the complete disappearance of the starting material is difficult to achieve, and side reactions are common. Yields of 50–95% are generally achieved in laboratory syntheses, while near-quantitative conversion can be achieved in industrial procedures.

ВВ Ullmann condensation. The Ullmann condensation is similar to the Williamson method except that the substrate is an aryl halide. Such reactions generally require a catalyst, such as copper.

ВВ Electrophilic addition of alcohols to alkenes. Alcohols add to electrophilically activated alkenes. Acid catalysis is required for this reaction. Often, mercury trifluoroacetate (Hg(OCOCF₃)₂) is used as a catalyst for the reaction generating an ether with Markovnikov regiochemistry. Using similar reactions, tetrahydropyranyl ethers are used as protective groups for alcohols.

Ether usage

В Ether is an organic compound that has sweet smell. Ether is colorless and evaporates very quickly when exposed to air. It catches fire very easily and needs to be handled with care. It is used as an antiseptic to prevent infection when an injection is administered. Cotton is dipped in ether and the skin is disinfected before an injection is allowed to pierce the skin.

ВВ At room temperature, ethers are pleasant-smelling colourless liquids. Relative to alcohols, ethers are generally less dense, less soluble in water, and have lower boiling points. They are relatively unreactive, and as a result they are useful as solvents for fats, oils, waxes, perfumes, resins, dyes, gums, and hydrocarbons. Vapours of certain ethers are used as insecticides, miticides, and fumigants for soil.

ВВ Ethers are also important in medicine and pharmacology, especially for use as anesthetics. For example, ethyl ether (CH₃CH₂в?’Oв?’CH₂CH₃), simply known as ether, was first used as a surgical anesthetic in 1842. Codeine, a potent pain-relieving drug, is the methyl ether of morphine. Because ether is highly flammable, it has largely been replaced by less-flammable anesthetics, including nitrous oxide (N₂O) and halothane (CF₃в?’CHClBr).

ВВ Ethyl ether is an excellent solvent for extractions and for a wide variety of chemical reactions. It is also used as a volatile starting fluid for diesel engines and gasoline engines in cold weather. Dimethyl ether is used as a spray propellant and refrigerant. Methyl t -butyl ether (MTBE) is a gasoline additive that boosts the octane number and reduces the amount of nitrogen-oxide pollutants in the exhaust. The ethers of ethylene glycol are used as solvents and plasticizers.

REVISION EXERCISES

Ex.1. Answer the following questions:

1. What are two varieties of ethers? 2. What are physical properties of ethers? 3. What catalysts are used for dehydration of ethers? 4. How long does a typical Williamson reaction proceed? 5. What are the most important ether reactions? 6. What is chemical reactivity of ethers? 7. Where are ethers used?

Ex.2. Match the words with their definitions:

1. anesthetics	a. the splitting of a complex molecule into simpler molecules; the breaking of a chemical bond in a molecule to give smaller molecules or radicals;
2. substituent	b. an atom, molecule, or ion that has unpaired valence electrons;
3. solvent	c. a chemical that is found in an air conditioner, a refrigerator, and in other equipment; a substance that undergoes phase transitions from a liquid to a gas and back again;
4. cleavage	d. a drug that causes a reversible loss of sensation; a substance that is usually administered to facilitate surgery;
5. anion	e. an atom or a group of atoms that take the position of another atom in a molecule;
6. radical	f. a substance that dissolves a solute (a chemically different liquid, solid, or gas) resulting in a solution;
7. refrigerant	g. an ion that has a negative charge, especially an ion that migrates to an anode in electrolysis.

Ex.3. Say whether the following statements are true or false:

1. Unlike alcohols ethers are not acidicВ and usually react with bases. 2. Ethers are susceptible to attack by halogen atoms and for this reason they are good solvents for radical reactions. 3. Ether molecules cannot form hydrogen bonds with each other and this results in low boiling points compared to alcohols. 4. Ethers are quite stable chemical compounds which easily react with bases, active metals and dilute acids. 5. The main reactions of ethers are acidic cleavage, peroxide formation, alpha-halogenation. 6) The Williamson ether synthesis is an organic reaction forming an ether from organohalide and alcohol. 7. At room temperature ethers are pungent-smelling liquids.

Ex.4. Insert the necessary word:

1. Ethers are organic compounds that contain an... atom connected to two alkyl or aryl groups. 2. One of the most common ethers is... ether. 3. Ethers are generally colourless... -smelling liquids at room temperature. 4. Hydrobromic and hydroiodic acids are especially useful for ether..., because both are strong acids and their anions are good nucleophiles. 5. Ethers are frequently employed as inert... in organic synthesis. 6. The solubility of ethers... with an increase in the number of carbon atoms. 7. Ether is used as... to prevent infection when an injection is administered. (cleavage, antiseptic, diethyl decreases, oxygen, sweet, solvents) ВВВВ

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