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15.1: Hydrocarbon Reactions Halogenation An alkane will react with a halogen to produce a halalkane and the corresponding hydrogen halide. The catalyst is ultraviolet radiation.

Reaction 1

methane chlorine chloromethane hydrogen chloride Reaction 2

propane bromine 2-bromopropane hydrogen bromide 1-bromopropane Notice that the second reaction has two possible haloalkanes. The halogen will replace any hydrogen in the alkane and so there would be two haloalkanes produced in this reaction: 2-bromopropane and 1-bromopropane Combustion Reactions Combustion is the process of burning in the presence of oxygen. It is the rapid reaction in which oxygen and alkanes may undergo complete or incomplete combustion. Complete combustion produces carbon dioxide and water. Incomplete combustion also produces carbon dioxide and water but also carbon soot and carbon monoxide. Crude petroleum, in the form of crude oil, is not very useful. It is a complex mixture of many aliphatic and aromatic compounds. In order to produce more useful alkanes and alkenes, the large alkanes are “cracked” into smaller alkanes and alkenes. With a catalyst and under high temperatures, large alkanes are cracked to produce smaller alkanes and alkenes. Catalytic reforming of crude petroleum converts aliphatic compounds into aromatic compounds. The following example shows the catalytic cracking and reforming of heptane in the presence of high temperatures and a catalyst.

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Alkene Reactions i.) Addition Reactions There are three types of addition reactions involving alkenes: hydrogenation, halogenation and hydrohalogenation. Each reaction name provides a clue as to the other reactant reacting with the alkene. All three are, respectively, are shown in the following reactions:

In each of the above cases, the double bond has been broken, allowing another atom to bond with the carbons that initially made up the double bond. In the case of hydrogenation, each carbon receives a hydrogen. In halogenation, each double bonded carbon receives a halogen. The hydrogen and halogen both bond with the carbons that were initially double bonded. Markovnikov’s Rule The symmetrical or the unsymmetrical structure of an alkene determines the products in the hydrohalogenation reaction. In a symmetrical alkene, there is only product. There is the possibility of two products when an unsymmetrical alkene undergoes a hydrohalogenation reaction. A symmetrical alkene refers to the similarity of the two carbons that form the double bond. If both carbons have the same structural arrangement, then there is symmetry. If one carbon, between the two that are double bonded, has a different arrangement, then it is unsymmetrical. Observe the following examples: Symmetrical Alkene

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Unsymmetrical Alkene

In the unsymmetrical alkene hydrohalogenation reaction, Markovnikov’s rule states that the double bonded carbon with more bonded hydrogens in the unsymmetrical alkene will attract the hydrogen more than the halogen. The halogen will gravitate to the double bonded carbon with the fewer hydrogens. The reaction between 1-octene and hydrogen bromide is:

Sample Problem: Complete the following reaction:

ii.) Hydration In the presence of a strong acid, an alkene will react with water to produce an alcohol. Notice that Markovnikov’s rule applies when an alkene is hydrated. Observe the following example: Example 1:

Example 2: The hydration of 1-methylcyclopentene is:

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iii.) Combustion Like alkanes, alkenes will undergo combustion to produce carbon dioxide and water. Alkyne Reactions i.) Acetylene Combustion and Preparation The most common alkyne is ethyne. It is more commonly known as acetylene, a flammable gas. Welders use acetylene in torches to weld metals. Its very hot flame can reach temperatures of around 3000°C. The combustion reaction is as follows:

2C2H2(g) + 5O2(g) →   4CO2(g) + 2H2O(l)

Acetylene can be prepared by reacting calcium carbide with water:

CaC2(s) + 2H2O(l) →   C2H2(g) + Ca(OH)2(aq)

Check out the following video. A demonstration of the explosive potential of even a small amount of acetylene mixed with the right amount of oxygen Acetylene Explosion Video ii.) Addition Reactions The following names of the types of reactions involving alkynes provide clues to the other reactant and the resulting product(s). Halogenation The halogenation of alkynes produces haloalkanes. The more common halogens are chlorine and bromine. Examine the following examples: Example:

Example: The reaction between 2-pentyne and bromine is:

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Hydrogenation The hydrogenation of an alkyne produces an alkane with the assistance of a nickel catalyst.

Example: The hydrogenation of propyne with a nickel catalyst is:

There are two other possibilities of hydrogenation of an alkyne: production of a cis and trans alkene.

Sample Problem: Show the hydrogenation of 2-butyne with a sodium and liquid ammonia catalyst.

Aromatic Hydrocarbons: Physical and Chemical Properties Benzene and other aromatic hydrocarbons are nonpolar. They are insoluble in water, but soluble in nonpolar solvents such as hexane, carbon tetrachloride, and ether. Benzene is considered to be carcinogenic (cancer-causing) and other compounds with multiple benzene rings bonded together are also considered carcinogenic. The boiling and melting points of aromatic compounds are typical of nonpolar organic compounds.

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Substitution Reactions Aromatics undergo substitution reactions with halogens, alkyl halides and nitric acid. Examine the following:

Example: The reaction between benzene and bromine is:

Sample Problem: Show the reaction between 1-chlorobutane and benzene.

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15.2: Other Carbon Functional Groups Reactions

A. Alcohols Reactions

Addition: Hydration of Alkenes

Alkenes reacting with water in the presence of an acid catalyst, will produce an alcohol. Commercially,

ethanol can be produced in this manner. Biologically, ethanol, through the activity of enzymes, can be

produced by the fermentation of carbohydrates (sugar or starch) in the absence of oxygen.

The following chemical reaction is the fermentation of a sugar:

The following reaction is the hydration of an alkene to produce an alcohol:

Sample Problem: Show the hydration of propene in the presence of sulphuric acid as a catalyst.

Elimination: Dehydration of an Alcohol

The dehydration of an alcohol is the reverse reaction of the hydration of an alkene. The dehydration of

an alcohol will produce an alkene.

Example: The following shows the dehydration of 1-hexanol:

Sample Problem: Show the dehydration of 1-butanol, at 180 °C, in the presence of concentrated

sulphuric acid as a catalyst.

Substitution: Reaction between an alcohol and a concentrated hydrohalogen acid.

Production of an alkyl halide is possible by reacting the corresponding hydrohalogen acid with an alcohol

with the addition of heat. The following example shows the substitution reaction between concentrated

hydrobromic acid and 1-butanol:

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Sample Problem: Show the reaction between concentrated hydrochloric acid and 1-propanol with the addition of heat. Reaction: Condensation Reaction between Alcohols Ethers can be produced by reacting two alcohols in the presence of sulphuric acid acting as a catalyst. Here is an example of two alcohols reacting where the hydrogen of one alcohol has dissociated and the –OH, hydroxyl, group of the other alcohol has dissociated to produce the ether.

CH3CH2CH2CH2OH + OHCH2CH2CH3 →   CH3CH2CH2CH2OCH2CH2CH3 Sample Problem: Name the two reacting alcohols and the ether in the same reaction.

CH3CH2CH2CH2OH + OHCH2CH2CH3 →   CH3CH2CH2CH2OCH2CH2CH3 B. Aldehydes and Ketones Reactions Aldehydes tend to be more reactive than ketones. Formaldehyde is the most reactive of the aldehydes and ketones. The reactivity of these carbonyl groups is due to the partial positive charge of the carbonyl carbon. Addition Reactions One type of addition reaction involves water. Both aldehydes and ketones produce alcohols with two –OH groups, diols. An equilibrium system is created when water reacts with these carbonyl groups. The reactions will proceed in the forward and reverse directions. Examples: The following reactions are just two examples:

propanone 2,2-propanediol

methanal methanediol

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Sample Problems: 1. Complete the following reaction by showing the structural formula and name of the product.

2. Show the structural formulas and the products for the reaction between 3-methyl-2-hexanone and water. Oxidation: Preparation of Aldehydes and Ketones from Alcohol. Alcohols can be converted into aldehydes and ketones under mild oxidation conditions. An alcohol at the end of the parent chain, taking part in a mild oxidation, will produce an aldehyde. An alcohol, where the hydroxy group is bonded to a carbon with other carbons, will produce a ketone under mild oxidizing conditions. Observe the following examples: Examples:

1-hexanol pentanal

3-hexanol 3-hexanone

Sample Problems: 1. Complete the following reaction by showing the structural formula and name of the product.

2. Show the structural formulas of the complete mild oxidation reaction of 2-butanol and give the name of the product.

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Carboxylic Acid Reactions Carboxylic acids can be prepared by the oxidation of normal alcohols and aldehydes using strong oxidants such as potassium permanganate, KMnO4, or potassium dichromate, K2Cr2O7. Since carboxylic compounds are acids, they do have the ability to undergo a neutralization reaction to produce an organic salt. Preparation The production of a carboxylic acid from a normal alcohol is a two step process. The oxidation of a normal alcohol can be shown with the reaction between ethanol and an oxidizing agent producing an aldehyde and in return the aldehyde oxidizes to produce a carboxylic acid. The production of acetic acid can take the following form: Step One:

ethanol ethanal

Step Two:

ethanal ethanoic acid

Did You Know? When wines turn sour, it is because of the oxidation of ethanol leading to the production of acetic acid. Sample Problems: Show the two step oxidation process of propanol.

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Neutralization Carboxylic acid is a weak acid. The hydrogen in the carboxyl group dissociates in an aqueous solution. This opens up the possibility of reacting with a base to produce an organic salt. Examine the following example showing the neutralization of acetic acid and sodium hydroxide. Example:

ethanoic acid sodium ethanoate

Sample Problem: Show the neutralization reaction between butanoic acid and sodium hydroxide. Esters Reactions The two types of reactions that will be covered in this activity are esterification, alnd hydrolysis of esters. The former concerns itself with the formation of esters. The hydrolysis of esters is the reverse reaction of esterification. Esterification Esterification is the reaction between an organic acid, carboxylic acid, and an alcohol using an acid as a catalyst and heat. The carboxyl group in the acid loses its –OH group and the alcohol loses the hydrogen from its –OH group. Water is the other product of the reaction. Note the reaction between salicylic acid and methanol.

Sample Problem: Show the esterification of hexanoic acid and ethanol.

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Amines and Amides Reactions

The relationship between amines and amides are at the opposite ends of a condensation reaction.

Condensation

Amines condense with carboxylic acids to produce amides.

In the following condensation reaction between a carboxylic acid and an amine, take note of the

hydroxyl group from the carboxylic acid detaching from its parent and reacting with the hydrogen

bonded to the nitrogen.

Sample Problem: Show the condensation reaction between propanoic acid and 2-(ethylamino)butane.

Polymers

Look around you. How many items do you see that are made out of plastic? You are surrounded. In your

everyday routine it is most likely that you will come across a polymer. Some examples of synthetic

polymers are Teflon, rubber, vulcanized rubber, polyethylene, and PVC.

Our DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are polymers.

Proteins, cellulose and starch are other natural polymers.

The term, polymer, refers to a very large molecule that consists of

repeating units called monomers. Poly means “many” and mer means

“part.” Mono means “one.”  The monomers are held together by covalent bonds.

Polymerization is the term referring to the chemical reaction that produces

a polymer. There are two ways: addition and condensation, depending on

the monomers that are taking part in the reaction. In the end, each

polymer has its own unique physical and chemical characteristics.

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Addition

Addition reactions involve monomers that contain carbon-carbon double bonds.

The simplest addition polymer is polyethylene whose starting alkene is ethane. The

double bond of ethene breaks and the carbons at each end have bonding

capabilities with the other ethene molecules that have their carbon-carbon double

bonds broken in the process. The structural formula for ethene is:

When the carbon-carbon double bond is broken then these monomer units take on the following

structure:

Condensation

The monomers used in condensation polymerization are difunctional. They have two functional groups

at each of their molecules. These reactive functional groups lend themselves to reaction. In a

condensation polymerization reaction there is a removal of a small molecule such as water. Some

examples of other products of condensation polymerization include wool, silk, cellulose, nylon and

starch.

The following is an example of a synthetic condensation polymerization reaction involving the

production of polyester from benzene-1,4-dicarboxylic acid and 2-ethanediol. The other product is

water.

Starch is a polysaccharide found in plants. It is composed of repeating monosaccharide units such as

glucose. The following example shows the participating atoms that together detach and allow a polymer

of starch to be formed from the glucose molecules.