introduction to organic chemistry: hydrocarbonsintroduction to organic chemistry: hydrocarbons ......

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Introduction to Organic Chemistry:HydrocarbonsChapter 12


Chapter 1212.1 – Organic Compounds

12.2 – Alkanes

12.3 – Alkanes with Substituents

12.4 – Properties of Alkanes

12.5 – Alkenes and Alkynes

12.6 – Cis-Trans Isomers

12.7 – Addition Reactions for Alkenes

12.8 – Aromatic Compounds

12.1 – Organic CompoundsIdentify properties characteristic of organic or inorganic compounds.

Organic CompoundsOrganic chemistry is the study of carbon compounds.An organic compound• Always contains carbon and hydrogen atoms• May also contain other nonmetals such as oxygen, nitrogen, phosphorus, or a halogen.

• Organic compounds are found in:• Gasoline, medicines, shampoos, plastics, and perfumes• Carbohydrates, fats, and proteins

Functional Groups• Organic compounds are organized by their functional groups (groups of

atoms bonded in a specific way).

• Compounds that contain the same functional groups have similar physical and chemical properties.

• The identification of functional groups allows us to classify organic compounds according to their structure, to name compounds within each family, and to predict their chemical reactions.


Organic vs. Inorganic• In chemistry, molecules are classified as Organic or Inorganic.

• Inorganic compounds are (quite expansively) anything that is not organic.

• Organic and Inorganic compounds have different properties.

– Organic compounds:Have low melting and boiling points.Are flammable and undergo combustion.Are not soluble in water.

– Inorganic compoundsMany inorganic compounds have high melting and boiling points.Inorganic compounds that are ionic are usually soluble in water, and most do not burn in air.



PracticeIdentify each characteristic as most typical of compounds that are inorganic or organic.

A. It has a high melting point.

B. It is not soluble in water.

C. It contains carbon and hydrogen atoms.

D. It has the formula MgCl2.

E. It burns easily in air.


Representations of Carbon Compounds• Hydrocarbons are organic compounds that consist of only carbon and hydrogen.

– In organic molecules, every carbon atom has four bonds. – In methane (CH4), the carbon atom forms an octet by sharing its four

valence electrons with four hydrogen atoms.

Three-dimensional and two-dimensional representations of methane: a) space-filling model, b) ball-and-stick model, c) wedge-dash model, d) expanded structural formula, and e) condensed structural formula


Representations of Carbon Compounds• In ethane (C2H6), each tetrahedral carbon forms three covalent bonds to hydrogen and one to the other carbon.


AlkanesAlkanes

• are formed by a continuous chain of carbon atoms.

• are named using the IUPAC (International Union of Pure and Applied Chemistry) system.

• have names that end in ane.

• use Greek prefixes to name carbon chains with five or more carbon atoms.


Study Check

In the butane molecule (C4H10), predict the shape around each carbon atom.

C

H

H

H C

H

H

C

H

H

C

H

H

H



12.2 – Alkanes








12.2 - AlkanesWrite the IUPAC names and draw the condensed or line-angle structural formulas for alkanes and cycloalkanes.


Alkanes

• More than 90% of the compounds in the world are organic compounds.

• The larger number of carbon compounds is possible because the covalent bonds between carbon atoms (C-C) is very strong, allowing carbon atoms to form long, stable chains.


Alkanes• The alkanes are a type of hydrocarbon in which the carbon atoms are connected only by single bonds.

– Alkanes are formed by a continuous chain of carbon atoms.– The names of alkanes and in –ane.

Such names are part of the IUPAC system (International Union of Pure and Applied Chemistry) used by chemists to name organic chemistry.

– Alkanes made of carbon chains are named based on how many carbons make up the chain.

– One of the most common uses of alkanes is as fuels.Methane, propane, octane, and hexane are all alkanes used as fuels.


IUPAC Names of Alkanes


Line-Angle Structural FormulasA simplified structure of organic molecules

• is called the line-angle structural formula.

• shows a zigzag line in which carbon atoms are represented as the ends of each line and as corners.

Carbon atoms

• at the end are bonded to three hydrogen atoms.

• in the middle are bonded to two hydrogen atoms.


Condensed formula and Line-angle formula

• Pentane


Condensed formula and Line-angle formula• Draw the condensed structural formula and name the molecule:


Guide to Drawing Structural Formulas for AlkanesStep 1: Draw the carbon chain.

Step 2: Draw the expanded structural formula by adding the hydrogen atoms using single bonds to each of the carbon atoms.

Step 3: Draw the condensed structural formula by combining the H atoms with each C atom.

Step 4: Draw the line-angle structural formula as a zigzag line in which the ends and corners represent C atoms.


Drawing Expanded, Condensed, and Line-Angle Structural Formulas (1 of 3)

Draw the expanded, condensed, and line-angle structural formula for pentane.

Step 1: Draw the carbon chain. A molecule of pentane has five carbon atoms in a continuous chain.

Step 2: Draw the expanded structural formula by adding the hydrogen atoms, using single bonds to each of the carbon atoms.




Step 3: Draw the condensed structural formula by combining the H atoms with each C atom.




Step 4: Draw the line-angle structural formula as a zigzag line in which the ends and corners represent C atoms.


Conformations of Alkanes• Single bonds can spin and rotate.

• Thus different arrangements, known as conformations, occur during the rotation about a single bond.

• http://symmetry.otterbein.edu/gallery/index.html


Structural Formulas: C4H10

As butane (C4H10) rotates, sometimes theline up in front of each other, and at other times they are opposite each other. Butane can be drawn using a variety of two-dimensional condensed structural formulas:


Structural Formulas: C4H10


Cycloalkanes

Hydrocarbons can also form into circles or rings called: cycloalkanes

• have two fewer hydrogen atoms than the open chain form.

• are named by using the prefix cyclo before the name of the alkane chain with the same number of carbon atoms.


Formulas of CycloalkanesTable 12.4 Formulas of Some Common CycloalkanesName BLANK BLANK BLANKCyclopropane Cyclobutane Cyclopentane Cyclohexane

Ball-and-Stick Model BLANK BLANK BLANKThree carbons single-bonded to each other in a triangular pattern, with each carbon single-bonded to 2 hydrogens.

The ball and stick model shows four carbons single-bonded to each other in a square pattern, with each carbon single-

bonded to 2 hydrogens.

The ball and stick model shows five carbons single-bonded to each other in a pentagonal pattern, with each carbon single-bonded to 2 hydrogens.

The ball and stick model shows six carbons single-bonded to each other in a hexagonal pattern, with each carbon

single-bonded to 2 hydrogens.

Condensed Structural Formula BLANK BLANK BLANKThe condensed structural formula shows a triangular ring of three C H 2 molecules.

The condensed structural formula shows a square ring of four C H 2 molecules.

The condensed structural formula shows a pentagonal ring of five C H 2

molecules.

The condensed structural formula shows a hexagonal ring of six C H 2 molecules.

Line-Angle Structural Formula BLANK BLANK BLANKThe line-angle structural formula is a triangle. The line-angle structural formula shows a

square.The line-angle structural formula shows

a pentagon. The line-angle structural formula shows a hexagon.


Study CheckGive the IUPAC name for each of the following compounds:

A.

B.


Study CheckName the following alkanes: A.

B.

C.

D.



12.2 – Alkanes








12.3 – Alkanes and SubstituentsWrite the IUPAC names for alkanes with substituents and draw their condensed and line-angle structural formulas.


Structural IsomersStructural isomers

• have the same molecular formula with a different arrangement of atoms.

• have the same number of atoms bonded in a different order.

Butane (C4H10) has two structural isomers: a straight chain and a branched chain.


Study Check Draw three possible structural isomers of pentane (C5H12).


Solution Draw three possible structural isomers of pentane (C5H12).

Structural Isomers of

C5H12

Structural Isomers of C5H12 Structural Isomers of C5H12

Structural Isomers of C5H12

CondensedThe first condensed structural formula is a straight chain of single-bonded molecules as follows. C H 3, C H 2, C H 2, C H 2, C H 3. The second condensed structural formula is a branched chain as follows. C H 3, C H single-bonded to C H 3 above,

C H 2, C H 3. The third condensed structural formula is a central C single-bonded to four C H 3 molecules above, below, rightward, and leftward.

Line-AngleThe line-angle structural formula shows a zigzag line made of 4 segments forming 3 angles. The line-angle structural formula shows a zigzag of 3 segments forming 2 angles, with

a fourth segment rising vertically from the first angle.The line-angle structural formula shows 2 rising and falling line segments with 2 segments rising diagonally right and left from the angle.


Study Check Is the pair of formulas structural isomers? Or the same molecule?


Substituents in Alkanes• When CH3 branches off of a carbon chain, it’s called an alkyl group

• When a halogen atom (Group 17) is attached to a carbon chain, it is named as a halo group with the terms –fluoro, -chloro, -bromo, -iodobased on which element it is.


Substituents and Alkyl Groups Table 12.5 Formulas and Names of Some Common Substituents

FormulaName

Formula, C H 3, single bond. name, methyl.Formula, straight chain, C H 3, C H 2, single bond. name, ethyl.

BLANK BLANK

FormulaName

Formula, straight chain, C H 3, C H 2, C H 2, single bond. name, propyl.

Formula, branched chain, C H 3, C H with single bond above, C

H 3. name, isopropyl. BLANK BLANK

FormulaName

Formula, straight chain, C H 3, C H 2, C H 2, C H 2, single bond. name, butyl.

Formula, branched chain, C H 3, C H single-bonded to C H 3 above, C H 2, single bond. name, isobutyl.

Formula, C H 3, C H with single bond above, C H 2, C H 3. name, secondary butyl.

Formula, central C with single bond above and three C H 3 molecules below, rightward, and leftward. name, tertiary butyl.

FormulaName

Formula, F, single bond. name, fluoro. Formula, F, single bond. name, fluoro. Formula, B r, single bond. name, bromo. Formula, I, single bond. name, iodo.


Naming Alkanes with Substituents


Naming Alkanes with Substituents


Naming Cycloalkanes with Substituents


Naming Cycloalkanes with Substituents


Naming HaloalkanesHaloalkanes

• are alakanes with a halogen atom that replaces a hydrogen atom.

• are named by putting the substituents in alphabetical order.

• have the halo group numbered according to the carbon where it is attached to the alkane.

Examples of Haloalkanes

BLANK BLANK BLANK BLANK

Formulastraight chain, C H 3, C l straight chain, C H 3, C H 2, B r Branched chain, C H 3, C H single-bonded to an F above A central C single-bonded to C l above and three C H 3 molecules below, rightward, and leftward

IUPAC Chloromethane Bromoethane 2-Fluoropropane 2-Chloro-2-methylpropane

Common Methyl chloride Ethyl bromide Isopropyl fluoride Tert-Butyl chloride


Drawing the molecule from the nameDraw the condensed and line-angle structural formulas for 2,3-dimethylbutane.


Drawing the molecule from the nameDraw the condensed and line-angle structural formulas for 2-bromo-3-ethyl-4-methylpentane.



12.2 – Alkanes








12.4 – Properties of AlkanesIdentify the properties of alkanes and write a balanced chemical equation for combustion.


Properties of AlkanesMany types of alkanes are the components of fuels that power our cars and oil that heats our home.

The solid alkanes that make up waxy coatings on fruits and vegetables help retain moisture, inhibit mold, and enhance appearance.

The different uses of alkane compounds result from their physical properties, including their solubility and density.


Uses of Alkanes (1 of 2)

Alkanes with one to four carbons are gases at room temperature and are widely used as heating fuels.

methane, ethane, propane, butane

Butane has four carbons:

Alkanes with five to eight carbons are highly volatile liquids at room temperature, which makes them useful as fuels.

pentane, hexane, heptane, octane

Octane has eight carbons:


Uses of Alkanes (2 of 2)

Alkanes with 9−17 carbons are liquids with higher boiling points and are found in motor oils, mineral oil, kerosene, diesel, and jet fuels.

Decane has 10 carbons:

• Alkanes with 18 or more carbon atoms, known as paraffins, are waxy solids at room temperature.

• Petroleum jelly, or Vaseline, is a semisolid mixture of hydrocarbons with more than 25 carbon atoms.


Melting and Boiling Points (1 of 4)

Alkanes

• have the lowest melting and boiling points of organic compounds.

• contain only the nonpolar bonds of • exhibit only weak dispersion forces in the solid and liquid states.

Longer-chain alkanes have more dispersion forces.



Branched alkanes

• have lower boiling points than the straight-chain isomers.



Branched alkanes

• have lower boiling points than the straight-chain isomers.

• tend to be more compact, reducing the points of contact between the molecules.

• do not have linear shapes and cannot line up close to each other.



Cycloalkanes

• have higher boiling points than the straight-chain alkanes with the same number of carbon atoms.

• have limited rotation of carbon bonds; they maintain their rigid structure and can be stacked closely together, which gives them many points of contact and attractions to each other.



We can compare the boiling points of straight-chain alkanes, branched-chain alkanes, and cycloalkanes.Table 12.6 Comparison of Boiling Points of Alkanes and Cycloalkanes with Five Carbons

Formula Name Boiling Point (°C)

Straight-Chain Alkane BLANK BLANKStraight chain alkanes. condensed structural formula, C H 3, C H 2, C H 2, C H 2, C H 3

Pentane 36

Branched-Chain Alkanes BLANK BLANKBranched chain alkanes. condensed structural formula, C H 3, C H single-bonded to C H 3, C H 2, C H 3

2-Methylbutane 28

Central C single-bonded to four C H 3 molecules

Dimethylpropane 10

Cycloalkane BLANK BLANKline-angle structural formula, a pentagonal ring

Cyclopentane 49


Combustion of Alkanes (1 of 3)

The carbon–carbon single bonds in alkanes are difficult to break, which makes them the least reactive family of organic compounds.

However, alkanes burn readily in oxygen to produce carbon dioxide, water, and energy.

Alkane O2 CO2 H2O + energyg g g g


Combustion of Alkanes (3 of 3)

Methane is the natural gas we use to cook our food and heat our homes. The equation for the combustion of methane (CH4) is written as follows:

4 2 2 2CH 2O CO 2H O + energyg g g g

Propane is the gas used in portable heaters and gas barbecues. The equation for the combustion of propane (C3H8) is written as follows:

4 2 2 2CH 5O 3CO 4H O + energyg g g g


Solubility and Density of AlkanesAlkanes are

• nonpolar.

• insoluble in water.

• less dense than water.

• flammable in air.

• found in crude oil.

If there is an oil spill in the ocean, the alkanes in the crude oil do not mix with the water but float on top, forming a thin layer on the surface.



12.2 – Alkanes








12.5 – Alkenes and AlkynesIdentify structural formulas as alkenes, cycloalkenes, and alkynes and write their IUPAC names.


Alkenes and AlkynesAlkenes are hydrocarbons that contain double bonds.

Alkynes are hydrocarbons that contain triple bonds

• are called unsaturated hydrocarbons because they do not contain the maximum number of hydrogen atoms.

• react with hydrogen gas to increase the number of hydrogen atoms and become alkanes.

Remember, carbon atoms always form four covalent bonds.


Identifying Alkenes

Alkenes contain one or more carbon–carbon double bonds.

In ethene (C2H4), two carbon atoms are connected by a double bond.

Each carbon atom in the double bond is attached to two hydrogen atoms and has a trigonal planar arrangement with bond angles of 120°.


Ethene (C2H4)Ethene (C2H4), more commonly called ethylene,

• is an important plant hormone involved in promoting the ripening of fruits such as bananas.

• accelerates the breakdown of cellulose in plants, which causes flowers to wilt and leaves to fall from trees.


Other alkene examples


Identifying AlkynesAlkynes contain one or more carbon–carbon triple bonds.In ethyne (C2H2),

• each carbon is also bonded to one H atom.

Each carbon atom in the triple bond has a linear arrangement with bond angles of 180°.


Ethyne (C2H2)Ethyne (C2H2), more commonly called acetylene

• Is used in welding where it reacts with oxygen to produce flames with temperatures above 3300°C


Other alkyne examples


Study Check (1 of 4)

Identify each of the following compounds as an alkene or alkyne:

A.

B.


Naming Alkanes, Alkenes, and AlkynesThe IUPAC names for alkenes and alkynes

• are similar to those of alkanes.

• use the alkane name with the same number of carbon atoms, replacing the ane ending with ene.

Cyclic alkenes are named as cycloalkenes.Table 12.7 Comparison of Names for Alkanes, Alkenes, and Alkynes


Study Check Write IUPAC name for the following:


Study Check Write IUPAC name for the following:


Solution (1 of 4)

Step 1: Name the longest carbon chain that contains the double or triple bond.

Analyze the ProblemGivenfive-carbon chain double bond, methyl groupNeedIUPAC name five carbon atoms—pentene

A.

Analyze the ProblemGivensix-carbon triple bondNeedIUPAC namesix carbon atoms—hexyne

B.


Solution (2 of 4)

Step 2: Number the carbon chain, starting from the end nearer the double or triple bond.

A.1

2

3

4

5

2-pentene

B.5

4 3 2 16

2-hexyne


Solution (3 of 4)

Step 3: Give the location and name of each substituent (alphabetical order) as a prefix to the alkeneor alkyne name.

A.1

2

3

4

5

4-methyl-2-pentene

B.5

4 3 2 16

2-hexyne; there are no substituents in this compound.


Naming CycloalkenesCycloalkenes have a double bond within a ring structure and

• are named by assigning the double bond to be between carbon 1 and carbon 2 when a substituent is on the ring.

• do not need to include the numbers for the double bond.

3-methylcyclopentene (It is understood that the double bond is between carbon 1 and carbon 2.)

The carbon atoms in the ring are numbered to give the double bond numbers 1 and 2 and the lowest possible number to any substituents present.



Name the following alkenes and alkynes:


Solution (4 of 4)

Name the following alkenes and alkynes:

cyclohexene 3,3-dimethylcyclopentene


Chemistry Link to the Environment: Fragrant Alkenes (1 of 2)

The odors you associate with lemons, oranges, roses, and lavender come from the volatile compounds that are synthesized by the plants that produce these flowers and fruits.Often these compounds contain double or triple bonds or ring structures; they are unsaturated.



12.2 – Alkanes








Cis–Trans Isomers In an alkene, the double bond is rigid and does not rotate.


Cis–Trans Isomers (1 of 2)

In an alkene, the double bond is rigid and does not rotate.

• holds attached groups in fixed positions.

• makes cis–trans isomers (geometric isomers) possible when two different groups are attached to the carbon atoms on each side of the double bond.

• requires a prefix of cis or trans to reflect the arrangement of groups across the double bond.


Cis–Trans Isomers Cis–trans isomers

• have different physical and chemical properties.


Cis–Trans Isomers of Butene• In a cis isomer, the alkyl groups are attached on the same side of the

double bond and H atoms are on the other side.

• In the trans isomer, the groups and H atoms are attached on opposite sides of the double bond.


Cis–Trans Isomers (2 of 2)

Cis–trans isomers

• cannot occur when two groups are the same on one of the carbons.


Chemistry Link to the Environment: Pheromones (1 of 2)

Many insects emit minute quantities of chemicals called pheromones to send others of the same species messages. Pheromones may

• warn an insect of danger.

• mark a trail.

• attract the opposite sex.


Chemistry Link to the Environment: Pheromones (2 of 2)

The effectiveness of many of these pheromones depends on the cis or trans configuration of the double bonds in the molecules.

One pheromone is bombykol,

• the sex pheromone produced by the female silkworm moth.

• which contains one cis double bond and one trans double bond.


Cis–Trans Isomers Identify each of the following as cis or trans


Naming Cis–Trans Isomers The prefix of cis or trans is placed in front of the alkene name when the compound is a cis or trans isomer.


Study CheckName, using cis or trans prefixes when needed.


SolutionName each, using cis or trans prefixes when needed.

A. cis-2,3-dichlorobutene

B. trans-2,3-dibromobutene

C. trans-2-butene



12.2 – Alkanes








12.7 – Addition Reactions for AlkenesDraw the condensed or line-angle structural formulas and give the names of the organic products of addition reactions of alkenes. Draw a condensed structural formula for a section of a polymer.


Addition Reactions• Alkanes are very stable and nonreactive.

• Alkenes and Alkynes, on the other hand, react readily with other molecules due to the double and triple bonds.

– These bonds act as an “electron source.” (Two electrons per bond.) – Addition reactions are the most common, where something is

added to each carbon in the double or triple bond.

• We will focus on alkenes, however these reactions can apply to alkynesas well.


Hydrogenation

• In hydrogenation, H atoms add to each of the carbon atoms in a double bond of an alkene.

• During hydrogenation, the double bonds are converted to single bondsof alkanes.

• A catalyst, such as platinum (Pt), nickel (Ni), or palladium (Pd) is used to speed up the reaction.


Practice


Hydration• In hydration, an alkene reactions with water (H-OH). A hydrogen atom (H-) from water forms a bond with one carbon atom in the double bond, and the oxygen atom in (-OH) forms a bond with the other carbon.

• The reaction is catalyzed by a strong acid, such as H2SO4, written as H+.

• Hydration is used to prepare alcohols, which have the hydroxyl (-OH) functional group.


Hydration – Markovnikov’s Rule• When water is added to an asymmetrical alkene, the H is added to the carbon with more H’s already attached. The –OH bonds to the other carbon.


Practice


Polymerization

• A polymer is a large molecule that consists of small repeating units called monomers.

• Many of these polymers are produced by addition reactions of alkenes.

• In the past hundred years, the plastics industry has made synthetic polymers such as those in carpeting, plastic wrap, nonstick pans, artificial joins, heart valves, and rain gear.


PolymerizationPolymerization is the addition, or connecting, of two alkenes, end-to-end.

These reactions require:– high temperature– a catalyst– higher pressure (over 1000 atm)

In an addition reaction, a polymer grows longer as each monomer is added at theend of the chain.




PracticeDraw a portion of a polymer made from polydichloroethene.



12.2 – Alkanes








12.8 – Aromatic CompoundsDescribe the bonding in benzene; name aromatic compounds, and draw their line-angle structural formulas.


Benzene• In 1825, Michael Faraday isolated a hydrocarbon called benzene.

• Benzene is:– An aromatic compound– A ring of six C atoms, each bonded to one H atom– A flat ring structure draw with three alternating double bonds.– Represented by two structures, because the electrons are shared

equally among all the C atoms– Represented by a line-angle structural formula using a cirl in the

center instead of alternating double bonds.


Aromatic Compounds• An aromatic compound is a compound with at least one benzene ring in it.

– This class was called aromatic because when they were initially discovered, it was found they often were the source of smells.


Naming Aromatic Compounds (1 of 5)

• Aromatic compounds containing a benzene ring and a single substituent are named as benzene derivatives.

• Since the ring contains only one substituent, the ring is not numbered.

• Some common names such as toluene, aniline, and phenol are allowed by IUPAC rules.



• When a benzene ring is a substituent, — C6H5, it is named as a phenyl group.



• When there are two or more substituents, the benzene ring is numbered to give the lowest numbers to the substituents

ortho, meta, para



• When a common name such as toluene, phenol, or aniline can be used,

– the carbon atom attached to the methyl, hydroxyl, or amine group is numbered as carbon 1.

– prefixes are used to show the position of the two substituents.



• The common name xylene is used for the isomers of dimethylbenzene.

• If three or more substituents are attached to the benzene ring, they are numbered in the direction to give the lowest set of numbers and then named alphabetically.



Select the correct name for each compound.

1.

A. chlorocyclohexane

B. chlorobenzeneC. 1-chlorobenzene

2.

A. 1,2-dimethylbenzene

B. 1,4-dimethylbenzeneC. 1,3-dimethylbenzene



12.2 – Alkanes








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