Depending on the type of hydrocarbon radical, as well as, in some cases, the characteristics of the attachment of the -OH group to this hydrocarbon radical, compounds with a hydroxyl functional group are divided into alcohols and phenols.

Alcohols are compounds in which the hydroxyl group is connected to a hydrocarbon radical, but is not attached directly to the aromatic ring, if there is one in the structure of the radical.

Examples of alcohols:

If the structure of a hydrocarbon radical contains an aromatic ring and a hydroxyl group, and is connected directly to the aromatic ring, such compounds are called phenols .

Examples of phenols:

Why are phenols classified as a separate class from alcohols? After all, for example, the formulas

are very similar and give the impression of substances of the same class of organic compounds.

However, the direct connection of the hydroxyl group with the aromatic ring significantly affects the properties of the compound, since the conjugated system of π-bonds of the aromatic ring is also conjugated with one of the lone electron pairs of the oxygen atom. Because of this, the O-H bond in phenols is more polar compared to alcohols, which significantly increases the mobility of the hydrogen atom in the hydroxyl group. In other words, phenols have much more pronounced acidic properties than alcohols.

Chemical properties of alcohols

Monohydric alcohols

Substitution reactions

Substitution of a hydrogen atom in the hydroxyl group

1) Alcohols react with alkali, alkaline earth metals and aluminum (cleaned from the protective film of Al 2 O 3), and metal alcoholates are formed and hydrogen is released:

The formation of alcoholates is possible only when using alcohols that do not contain water dissolved in them, since in the presence of water alcoholates are easily hydrolyzed:

CH 3 OK + H 2 O = CH 3 OH + KOH

2) Esterification reaction

The esterification reaction is the interaction of alcohols with organic and oxygen-containing inorganic acids, leading to the formation of esters.

This type of reaction is reversible, therefore, to shift the equilibrium towards the formation of an ester, it is advisable to carry out the reaction with heating, as well as in the presence of concentrated sulfuric acid as a water-removing agent:

Substitution of hydroxyl group

1) When alcohols are exposed to hydrohalic acids, the hydroxyl group is replaced by a halogen atom. As a result of this reaction, haloalkanes and water are formed:

2) By passing a mixture of alcohol vapor and ammonia through heated oxides of some metals (most often Al 2 O 3), primary, secondary or tertiary amines can be obtained:

The type of amine (primary, secondary, tertiary) will depend to some extent on the ratio of the starting alcohol to ammonia.

Elimination reactions

Dehydration

Dehydration, which actually involves the elimination of water molecules, in the case of alcohols differs by intermolecular dehydration And intramolecular dehydration.

At intermolecular dehydration In alcohols, one molecule of water is formed as a result of the abstraction of a hydrogen atom from one molecule of alcohol and a hydroxyl group from another molecule.

As a result of this reaction, compounds belonging to the class of ethers (R-O-R) are formed:

Intramolecular dehydration alcohols process occurs in such a way that one molecule of water is split off from one molecule of alcohol. This type of dehydration requires somewhat more stringent conditions, consisting in the need to use significantly stronger heating compared to intermolecular dehydration. In this case, from one molecule of alcohol one molecule of alkene and one molecule of water are formed:

Since the methanol molecule contains only one carbon atom, intramolecular dehydration is impossible for it. When methanol is dehydrated, only ether (CH 3 -O-CH 3) can be formed.

It is necessary to clearly understand the fact that in the case of dehydration of unsymmetrical alcohols, intramolecular elimination of water will proceed in accordance with Zaitsev’s rule, i.e. hydrogen will be removed from the least hydrogenated carbon atom:

Dehydrogenation of alcohols

a) Dehydrogenation of primary alcohols when heated in the presence of copper metal leads to the formation aldehydes:

b) In the case of secondary alcohols, similar conditions will lead to the formation ketones:

c) Tertiary alcohols do not enter into a similar reaction, i.e. are not subject to dehydrogenation.

Oxidation reactions

Combustion

Alcohols easily react in combustion. This generates a large amount of heat:

2CH 3 -OH + 3O 2 = 2CO 2 + 4H 2 O + Q

Incomplete oxidation

Incomplete oxidation of primary alcohols can lead to the formation of aldehydes and carboxylic acids.

In the case of incomplete oxidation of secondary alcohols, only ketones can be formed.

Incomplete oxidation of alcohols is possible when they are exposed to various oxidizing agents, for example, air oxygen in the presence of catalysts (metallic copper), potassium permanganate, potassium dichromate, etc.

In this case, aldehydes can be obtained from primary alcohols. As you can see, the oxidation of alcohols to aldehydes essentially leads to the same organic products as dehydrogenation:

It should be noted that when using oxidizing agents such as potassium permanganate and potassium dichromate in an acidic environment, deeper oxidation of alcohols is possible, namely to carboxylic acids. In particular, this manifests itself when using an excess of oxidizing agent during heating. Secondary alcohols can only be oxidized to ketones under these conditions.

LIMITED POLYATHICAL ALCOHOLS

Substitution of hydrogen atoms of hydroxyl groups

Polyhydric alcohols are the same as monohydric ones react with alkali, alkaline earth metals and aluminum (removed from filmAl 2 O 3 ); in this case, a different number of hydrogen atoms of hydroxyl groups in the alcohol molecule can be replaced:

2. Since the molecules of polyhydric alcohols contain several hydroxyl groups, they influence each other due to a negative inductive effect. In particular, this leads to a weakening of the O-H bond and an increase in the acidic properties of hydroxyl groups.

B O The greater acidity of polyhydric alcohols is manifested in the fact that polyhydric alcohols, unlike monohydric alcohols, react with some hydroxides of heavy metals. For example, you need to remember the fact that freshly precipitated copper hydroxide reacts with polyhydric alcohols to form a bright blue solution of the complex compound.

Thus, the interaction of glycerol with freshly precipitated copper hydroxide leads to the formation of a bright blue solution of copper glycerate:

This reaction is quality for polyhydric alcohols. To pass the Unified State Exam, it is enough to know the signs of this reaction, but it is not necessary to be able to write the interaction equation itself.

3. Just like monohydric alcohols, polyhydric alcohols can enter into an esterification reaction, i.e. react with organic and oxygen-containing inorganic acids with the formation of esters. This reaction is catalyzed by strong inorganic acids and is reversible. In this regard, when carrying out the esterification reaction, the resulting ester is distilled off from the reaction mixture in order to shift the equilibrium to the right according to Le Chatelier’s principle:

If carboxylic acids with a large number of carbon atoms in the hydrocarbon radical react with glycerol, the resulting esters are called fats.

In the case of esterification of alcohols with nitric acid, a so-called nitrating mixture is used, which is a mixture of concentrated nitric and sulfuric acids. The reaction is carried out under constant cooling:

An ester of glycerol and nitric acid, called trinitroglycerin, is an explosive. In addition, a 1% solution of this substance in alcohol has a powerful vasodilating effect, which is used for medical indications to prevent a stroke or heart attack.

Substitution of hydroxyl groups

Reactions of this type proceed through the mechanism of nucleophilic substitution. Interactions of this kind include the reaction of glycols with hydrogen halides.

For example, the reaction of ethylene glycol with hydrogen bromide proceeds with the sequential replacement of hydroxyl groups by halogen atoms:

Chemical properties of phenols

As mentioned at the very beginning of this chapter, the chemical properties of phenols are markedly different from the chemical properties of alcohols. This is due to the fact that one of the lone electron pairs of the oxygen atom in the hydroxyl group is conjugated with the π-system of conjugated bonds of the aromatic ring.

Reactions involving the hydroxyl group

Acid properties

Phenols are stronger acids than alcohols and are dissociated to a very small extent in aqueous solution:

B O The greater acidity of phenols compared to alcohols in terms of chemical properties is expressed in the fact that phenols, unlike alcohols, are able to react with alkalis:

However, the acidic properties of phenol are less pronounced than even one of the weakest inorganic acids - carbonic acid. Thus, in particular, carbon dioxide, when passing it through an aqueous solution of alkali metal phenolates, displaces free phenol from the latter as an even weaker acid than carbonic acid:

Obviously, any other stronger acid will also displace phenol from phenolates:

3) Phenols are stronger acids than alcohols, and alcohols react with alkali and alkaline earth metals. In this regard, it is obvious that phenols will react with these metals. The only thing is that, unlike alcohols, the reaction of phenols with active metals requires heating, since both phenols and metals are solids:

Substitution reactions in the aromatic ring

The hydroxyl group is a substituent of the first kind, which means that it facilitates the occurrence of substitution reactions in ortho- And pair- positions in relation to oneself. Reactions with phenol occur under much milder conditions compared to benzene.

Halogenation

The reaction with bromine does not require any special conditions. When bromine water is mixed with a phenol solution, a white precipitate of 2,4,6-tribromophenol is instantly formed:

Nitration

When phenol is exposed to a mixture of concentrated nitric and sulfuric acids (nitrating mixture), 2,4,6-trinitrophenol is formed, a yellow crystalline explosive:

Addition reactions

Since phenols are unsaturated compounds, they can be hydrogenated in the presence of catalysts to the corresponding alcohols.

Alcohols are complex organic compounds, hydrocarbons, necessarily containing one or more hydroxyls (OH- groups) associated with a hydrocarbon radical.

History of discovery

According to historians, already 8 centuries BC, people were drinking drinks containing ethyl alcohol. They were obtained by fermenting fruit or honey. In its pure form, ethanol was isolated from wine by the Arabs around the 6th-7th centuries, and by Europeans five centuries later. In the 17th century, methanol was obtained by distilling wood, and in the 19th century, chemists discovered that alcohols are a whole category of organic substances.

Classification

— Based on the number of hydroxyls, alcohols are divided into one-, two-, three-, and polyhydric. For example, monohydric ethanol; trihydric glycerol.
- Based on the number of radicals associated with the carbon atom connected to the OH- group, alcohols are divided into primary, secondary, and tertiary.
- Based on the nature of the radical bonds, alcohols are saturated, unsaturated, or aromatic. In aromatic alcohols, the hydroxyl is not connected directly to the benzene ring, but through other radical(s).
— Compounds in which OH— is directly linked to the benzene ring are considered a separate class of phenols.

Properties

Depending on how many hydrocarbon radicals are in the molecule, alcohols can be liquid, viscous, or solid. Water solubility decreases with increasing number of radicals.

The simplest alcohols are mixed with water in any proportions. If the molecule contains more than 9 radicals, then they do not dissolve in water at all. All alcohols dissolve well in organic solvents.
— Alcohols burn, releasing a large amount of energy.
- They react with metals, resulting in the formation of salts - alcoholates.
— Interact with bases, exhibiting the qualities of weak acids.
— React with acids and anhydrides, exhibiting basic properties. The reactions result in esters.
— Exposure to strong oxidizing agents leads to the formation of aldehydes or ketones (depending on the type of alcohol).
— Under certain conditions, ethers, alkenes (compounds with a double bond), halohydrocarbons, amines (hydrocarbons derived from ammonia) are obtained from alcohols.

Alcohols are toxic to the human body, some are poisonous (methylene, ethylene glycol). Ethylene has a narcotic effect. Alcohol vapors are also dangerous, so work with alcohol-based solvents must be carried out in compliance with safety precautions.

However, alcohols participate in the natural metabolism of plants, animals and humans. The category of alcohols includes such vital substances as vitamins A and D, steroid hormones estradiol and cortisol. More than half of the lipids that supply energy to our body are based on glycerol.

Application

— In organic synthesis.
— Biofuels, fuel additives, brake fluid ingredient, hydraulic fluids.
- Solvents.
— Raw materials for the production of surfactants, polymers, pesticides, antifreeze, explosives and toxic substances, household chemicals.
— Fragrant substances for perfumery. Included in cosmetic and medical products.
— Base of alcoholic beverages, solvent for essences; sweetener (mannitol, etc.); coloring (lutein), flavoring (menthol).

In our store you can buy different types of alcohols.

Butyl alcohol

Monohydric alcohol. Used as a solvent; plasticizer at production of polymers; formaldehyde resin modifier; raw materials for organic synthesis and production of fragrant substances for perfumery; fuel additives.

Furfuryl alcohol

Monohydric alcohol. In demand for the polymerization of resins and plastics, as a solvent and film former in paint and varnish products; raw materials for organic synthesis; binding and compacting agent in the production of polymer concrete.

Isopropyl alcohol (2-propanol)

Secondary monohydric alcohol. It is actively used in medicine, metallurgy, and the chemical industry. A substitute for ethanol in perfumes, cosmetics, disinfectants, household chemicals, antifreeze, and cleaners.

Ethylene glycol

Dihydric alcohol. Used in the production of polymers; paints for printing houses and textile production; It is part of antifreeze, brake fluids, and coolants. Used for drying gases; as a raw material for organic synthesis; solvent; a means for cryogenic “freezing” of living organisms.

Glycerol

Trihydric alcohol. In demand in cosmetology, food industry, medicine, as a raw material in org. synthesis; for the manufacture of nitroglycerin explosive. It is used in agriculture, electrical engineering, textile, paper, leather, tobacco, paint and varnish industries, in the production of plastics and household chemicals.

Mannitol

Hexahydric (polyhydric) alcohol. Used as a food additive; raw materials for the manufacture of varnishes, paints, drying oils, resins; is part of surfactants and perfume products.

DEFINITION

Alcohols– compounds containing one or more hydroxyl groups –OH associated with a hydrocarbon radical.

The general formula of the homologous series of saturated monohydric alcohols is C n H 2 n +1 OH. The names of alcohols contain the suffix – ol.

Depending on the number of hydroxyl groups, alcohols are divided into one- (CH 3 OH - methanol, C 2 H 5 OH - ethanol), two- (CH 2 (OH)-CH 2 -OH - ethylene glycol) and triatomic (CH 2 (OH )-CH(OH)-CH 2 -OH - glycerol). Depending on which carbon atom the hydroxyl group is located at, primary (R-CH 2 -OH), secondary (R 2 CH-OH) and tertiary alcohols (R 3 C-OH) are distinguished.

Saturated monohydric alcohols are characterized by isomerism of the carbon skeleton (starting from butanol), as well as isomerism of the position of the hydroxyl group (starting from propanol) and interclass isomerism with ethers.

CH 3 -CH 2 -CH 2 -CH 2 -OH (butanol – 1)

CH 3 -CH (CH 3) - CH 2 -OH (2-methylpropanol - 1)

CH 3 -CH (OH) -CH 2 -CH 3 (butanol - 2)

CH 3 -CH 2 -O-CH 2 -CH 3 (diethyl ether)

Chemical properties of alcohols

1. Reactions that occur with the rupture of the O-H bond:

— the acidic properties of alcohols are very weakly expressed. Alcohols react with alkali metals

2C 2 H 5 OH + 2K → 2C 2 H 5 OK + H 2

but do not react with alkalis. In the presence of water, alcoholates are completely hydrolyzed:

C 2 H 5 OK + H 2 O → C 2 H 5 OH + KOH

This means that alcohols are weaker acids than water.

- formation of esters under the influence of mineral and organic acids:

CH 3 -CO-OH + H-OCH 3 ↔ CH 3 COOCH 3 + H 2 O

- oxidation of alcohols under the action of potassium dichromate or permanganate to carbonyl compounds. Primary alcohols are oxidized to aldehydes, which in turn can be oxidized to carboxylic acids.

R-CH 2 -OH + [O] → R-CH = O + [O] → R-COOH

Secondary alcohols are oxidized to ketones:

R-CH(OH)-R’ + [O] → R-C(R’) = O

Tertiary alcohols are more resistant to oxidation.

2. Reaction with breaking of the C-O bond.

- intramolecular dehydration with the formation of alkenes (occurs when alcohols with water-removing substances (concentrated sulfuric acid) are strongly heated):

CH 3 -CH 2 -CH 2 -OH → CH 3 -CH = CH 2 + H 2 O

— intermolecular dehydration of alcohols with the formation of ethers (occurs when alcohols are slightly heated with water-removing substances (concentrated sulfuric acid)):

2C 2 H 5 OH → C 2 H 5 -O-C 2 H 5 + H 2 O

— weak basic properties of alcohols manifest themselves in reversible reactions with hydrogen halides:

C 2 H 5 OH + HBr → C 2 H 5 Br + H 2 O

Physical properties of alcohols

Lower alcohols (up to C 15) are liquids, higher alcohols are solids. Methanol and ethanol are mixed with water in any ratio. As the molecular weight increases, the solubility of alcohols in alcohol decreases. Alcohols have high boiling and melting points due to the formation of hydrogen bonds.

Preparation of alcohols

The production of alcohols is possible using a biotechnological (fermentation) method from wood or sugar.

Laboratory methods for producing alcohols include:

- hydration of alkenes (the reaction occurs when heated and in the presence of concentrated sulfuric acid)

CH 2 = CH 2 + H 2 O → CH 3 OH

— hydrolysis of alkyl halides under the influence of aqueous solutions of alkalis

CH 3 Br + NaOH → CH 3 OH + NaBr

CH 3 Br + H 2 O → CH 3 OH + HBr

— reduction of carbonyl compounds

CH 3 -CH-O + 2[H] → CH 3 – CH 2 -OH

Examples of problem solving

EXAMPLE 1

Exercise	The mass fractions of carbon, hydrogen and oxygen in the molecule of saturated monohydric alcohol are 51.18, 13.04 and 31.18%, respectively. Derive the formula of alcohol.
Solution	Let us denote the number of elements included in the alcohol molecule by the indices x, y, z. Then, the formula of alcohol in general will look like C x H y O z. Let's write down the ratio: x:y:z = ω(С)/Ar(C): ω(Н)/Ar(Н) : ω(О)/Ar(О); x:y:z = 51.18/12: 13.04/1: 31.18/16; x:y:z = 4.208: 13.04: 1.949. Let's divide the resulting values ​​by the smallest, i.e. at 1.949. We get: x:y:z = 2:6:1. Therefore, the formula of alcohol is C 2 H 6 O 1. Or C 2 H 5 OH is ethanol.
Answer	The formula of saturated monohydric alcohol is C 2 H 5 OH.

Alcohols are hydrocarbon derivatives containing one or more -OH groups, called a hydroxyl group or hydroxyl.

Alcohols are classified:

1. According to the number of hydroxyl groups contained in the molecule, alcohols are divided into monohydric (with one hydroxyl), diatomic (with two hydroxyls), triatomic (with three hydroxyls) and polyatomic.

Like saturated hydrocarbons, monohydric alcohols form a naturally constructed series of homologues:

As in other homologous series, each member of the alcohol series differs in composition from the previous and subsequent members by a homologous difference (-CH 2 -).

2. Depending on which carbon atom the hydroxyl is located at, primary, secondary and tertiary alcohols are distinguished. The molecules of primary alcohols contain a -CH 2 OH group associated with one radical or with a hydrogen atom in methanol (hydroxyl at the primary carbon atom). Secondary alcohols are characterized by a >CHOH group linked to two radicals (hydroxyl at the secondary carbon atom). In the molecules of tertiary alcohols there is a >C-OH group associated with three radicals (hydroxyl at the tertiary carbon atom). Denoting the radical by R, we can write the formulas of these alcohols in general form:

In accordance with the IUPAC nomenclature, when constructing the name of a monohydric alcohol, the suffix -ol is added to the name of the parent hydrocarbon. If a compound contains higher functions, the hydroxyl group is designated by the prefix hydroxy- (in Russian the prefix oxy- is often used). The longest unbranched chain of carbon atoms, which includes a carbon atom bound to a hydroxyl group, is selected as the main chain; if the compound is unsaturated, then a multiple bond is also included in this chain. It should be noted that when determining the beginning of numbering, the hydroxyl function usually takes precedence over the halogen, double bond and alkyl, therefore, numbering begins from the end of the chain closer to which the hydroxyl group is located:

The simplest alcohols are named by the radicals with which the hydroxyl group is connected: (CH 3) 2 CHOH - isopropyl alcohol, (CH 3) 3 SON - tert-butyl alcohol.

A rational nomenclature for alcohols is often used. According to this nomenclature, alcohols are considered as derivatives of methyl alcohol - carbinol:

This system is convenient in cases where the name of the radical is simple and easy to construct.

2. Physical properties of alcohols

Alcohols have higher boiling points and are significantly less volatile, have higher melting points, and are more soluble in water than the corresponding hydrocarbons; however, the difference decreases with increasing molecular weight.

The difference in physical properties is due to the high polarity of the hydroxyl group, which leads to the association of alcohol molecules due to hydrogen bonding:

Thus, the higher boiling points of alcohols compared to the boiling points of the corresponding hydrocarbons are due to the need to break hydrogen bonds when molecules pass into the gas phase, which requires additional energy. On the other hand, this type of association leads to an increase in molecular weight, which naturally causes a decrease in volatility.

Alcohols with low molecular weight are highly soluble in water, this is understandable if we take into account the possibility of forming hydrogen bonds with water molecules (water itself is associated to a very large extent). In methyl alcohol, the hydroxyl group makes up almost half the mass of the molecule; It is not surprising, therefore, that methanol is miscible with water in all respects. As the size of the hydrocarbon chain in alcohol increases, the influence of the hydroxyl group on the properties of alcohols decreases; accordingly, the solubility of substances in water decreases and their solubility in hydrocarbons increases. The physical properties of monohydric alcohols with high molecular weight are already very similar to the properties of the corresponding hydrocarbons.

DEFINITION

Saturated monohydric alcohols can be considered as derivatives of hydrocarbons of the methane series, in the molecules of which one hydrogen atom is replaced by a hydroxyl group.

So, saturated monohydric alcohols consist of a hydrocarbon radical and the -OH functional group. In the names of alcohols, the hydroxyl group is designated by the suffix -ol.

The general formula of saturated monohydric alcohols is C n H 2 n +1 OH or R-OH or C n H 2 n +2 O. The molecular formula of an alcohol does not reflect the structure of the molecule, since two completely different substances can correspond to the same gross formula, for example, the molecular formula C 2 H 5 OH is common to both ethyl alcohol and acetone (dimethyl ketone):

CH 3 -CH 2 -OH (ethanol);

CH 3 -O-CH 3 (acetone).

Just like the hydrocarbons of the methane series, saturated monohydric alcohols form a homologous series of methanol.

Let's compose this series of homologues and consider the patterns of changes in the physical properties of compounds of this series depending on the increase in the hydrocarbon radical (Table 1).

Homologous series (incomplete) of saturated monohydric alcohols

Table 1. Homologous series (incomplete) of saturated monohydric alcohols.

Saturated monohydric alcohols are lighter than water because their density is less than unity. Lower alcohols are miscible with water in all respects; as the hydrocarbon radical increases, this ability decreases. Most alcohols are highly soluble in organic solvents. Alcohols have higher boiling and melting points than the corresponding hydrocarbons or halogen derivatives, which is due to the possibility of their formation of intermolecular bonds.

The most important representatives of saturated monohydric alcohols are methanol (CH 3 OH) and ethanol (C 2 H 5 OH).

Examples of problem solving

EXAMPLE 1

Exercise	In natural pearls, the mass ratio of calcium, carbon and oxygen is 10:3:12. What is the simplest formula for pearls?
Solution	In order to find out in what relationships the chemical elements in the molecule are located, it is necessary to find their amount of substance. It is known that to find the amount of a substance one should use the formula: Let's find the molar masses of calcium, carbon and oxygen (we'll round the values ​​of relative atomic masses taken from D.I. Mendeleev's Periodic Table to whole numbers). It is known that M = Mr, which means M(Ca) = 40 g/mol, Ar(C) = 12 g/mol, and M(O) = 32 g/mol. Then, the amount of substance of these elements is equal to: n (Ca) = m (Ca) / M (Ca); n (Ca) = 10 / 40 = 0.25 mol. n(C) = m(C)/M(C); n(C) = 3/12 = 0.25 mol. n(O) = m(O)/M(O); n(O) = 12/16 = 0.75 mol. Let's find the molar ratio: n(Ca) :n(C):n(O) = 0.25: 0.25: 0.75= 1: 1: 3, those. The formula of the pearl compound is CaCO 3.
Answer	CaCO3

EXAMPLE 2

Exercise	Nitric oxide contains 63.2% oxygen. What is the formula of the oxide
Solution	The mass fraction of element X in a molecule of the composition NX is calculated using the following formula: ω (X) = n × Ar (X) / M (HX) × 100%. Let's calculate the mass fraction of nitrogen in the oxide: ω(N) = 100% - ω(O) = 100% - 63.2% = 36.8%. Let us denote the number of moles of elements included in the compound by “x” (nitrogen) and “y” (oxygen). Then, the molar ratio will look like this (the values ​​of relative atomic masses taken from D.I. Mendeleev’s Periodic Table are rounded to whole numbers): x:y = ω(N)/Ar(N) : ω(O)/Ar(O); x:y= 36.8/14: 63.2/16; x:y= 2.6: 3.95 = 1: 2. This means that the formula for the compound of nitrogen and oxygen will be NO 2. This is nitric oxide (IV).
Answer	NO 2