Chapter 10 Introduction to Organic Chemistry: Alkanes 10.1...

Chapter 10 Introduction to Organic Chemistry: Alkanes

10.1 Organic Compounds

Organic Chemistry

An organic compound

• is a compound made from carbon atoms.• has one or more C atoms. • has many H atoms.• may also contain O, S, N, and halogens.

Organic Compounds

Typical organic compounds

• have covalent bonds.• have low melting points.• have low boiling points.• are flammable.• are soluble in nonpolar

solvents.• are not soluble in water.

Organic vs. Inorganic

• Propane, C3H8, is an organic compound used as a fuel.

• NaCl, salt, is an inorganic compound composed of Na+ and Cl− ions.

Why is propane organic,but NaCl is not?

Comparing Organic and Inorganic Compounds

Learning Check

Identify each characteristic as most typical of compoundsthat are 1) inorganic or 2) organic.

A. has a high melting point. B. is not soluble in water.C. has a formula CH3─CH2─CH3.D. has a formula MgCl2.E. burns easily in air.F. has covalent bonds.

Solution

Identify each characteristic as most typical of compoundsthat are 1) inorganic or 2) organic.

1 A. has a high melting point. 2 B. is not soluble in water.2 C. has a formula CH3─CH2─CH3.1 D. has a formula MgCl2.2 E. burns easily in air.2 F. has covalent bonds.

Writing Formulas for Alkanes

In organic compounds, • carbon has 4 valence electrons and hydrogen has 1.

•• C • H ••

• carbon achieves an octet by forming four bonds. H H• •

H : C : H H C H• •

H H CH4, methane

Tetrahedral Structure of Carbon

VSEPR theorypredicts that a carbon atom with four single, covalent bonds has a tetrahedral shape.

Organic Molecules

In organic molecules, • valence electrons are shared.• covalent bonds form between carbon atoms.

H H H H• • • •

H : C : C : H H C C H• • • •H H H H

Ethane, CH3─CH3

Tetrahedral Structure of Carbon

In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape.

10.2 Alkanes

Structural Formulas

Alkanes are written with structural formulas that are• expanded to show each bond.• condensed to show each carbon atom and its

attached hydrogen atoms.

Expanded CondensedH

H C H CH4 , methane

Expanded and Condensed Structures

Structural Formulas

Condensed formulas are written for expanded structural formula by showing each carbon and the attached hydrogen atoms.Expanded Condensed

H H H H│ │ │ │

H─C ─C ─C ─C ─ H CH3─CH2─CH2─CH3

│ │ │ │H H H H

Names of Alkanes

The names of alkanes• are determined by the IUPAC (International Union of

Pure and Applied Chemistry) system.• end in –ane.• with 1-4 carbons in a chain use prefixes as follows:

Name # Carbons Condensed Structural Formula

Methane 1 CH4

Ethane 2 CH3―CH3

Propane 3 CH3―CH2―CH3

Butane 4 CH3―CH2―CH2―CH3

Names of Alkanes

Alkanes with 5-10 carbon atoms in a chain use Greek prefixes.Name # Carbons Structural FormulaPentane 5 CH3CH2CH2CH2CH3

Hexane 6 CH3CH2CH2CH2CH2CH3

Heptane 7 CH3CH2CH2CH2CH2CH2CH3

Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3

Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3

Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Learning Check

A. Write the condensed formula for:H H H H H

H C C C C C H

H H H H HB. What is its molecular formula?C. What is its name?

Solution

A. CH3─CH2─CH2─CH2─CH3

B. C5H12

C. pentane

Writing Structural Formulas

Carbon atoms in a chain

• maintain tetrahedral shape.• are connected in a zigzag pattern.• are drawn as 2-dimensional. • can be written in several conformations.

Some Structures for Butane

Hexane Has Six Carbon Atoms

Hexane • is an alkane with six carbon atoms in a continuous

chain.• has a “zigzag” look because each carbon atom is at

the center of a tetrahedron.• is represented by a ball-and-stick model as shown

below.

Learning Check

Write the condensed structural formula for

A. ethane.

B. heptane.

Solution

Write the condensed structural formula for

A. ethane CH3─CH3

B. heptane CH3─CH2─CH2─CH2─CH2─CH2─CH3

Cycloalkanes

• are cyclic alkanes.

• have two hydrogen atoms fewer than the open chain.

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

Cycloalkanes

The structural formulas of cycloalkanes are usually represented by geometric figures.

More Cycloalkanes

Learning Check

Name the following.

A. CH3─CH2─CH2─CH3

C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3

Solution

Name the following:

A. CH3─CH2─CH2─CH3 butane

B. cyclopropane

C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3 octane

D. cyclohexane

10.3 Alkanes with Substituents

Isomers of Butane

Isomers• have the same

molecular formula.• have different atom

arrangements.• of butane (C4H10) are a

straight chain and a branched chain.

Alkyl groups

Alkyl groups are• alkanes that are missing one H. • substituents attached to carbon chains.• named with a –yl ending.

CH3 methyl

CH3 CH2 ethyl

Naming Substituents

In the IUPAC system,• a carbon branch is

named as an alkyl group.

• halogen atoms are named as halo.

Guide to Naming Alkanes

Alkanes with Substituents

CH3 CH CH3 methylpropane

methyl groupsCH3 CH3

CH3 CH CH2 CH CH3 2,4-dimethylpentane

Naming Alkanes

Give the name of CH3 CH3

CH3─CH─CH─CH3

STEP 1: Name the longest continuous chain.

CH3 CH3

CH3─CH─CH─CH3

butane

Naming Alkanes

Give the name of CH3 CH3

CH3─CH─CH─CH3

STEP 2: Number chain. CH3 CH3

CH3─CH─CH─CH31 2 3 4

STEP 3: Locate substituents and name.2,3-dimethylbutane

Learning Check

Write the name of

Cl CH3

CH3─CH2─CH─CH─CH3

Solution

STEP 1: Longest chain is pentane.

STEP 2: Number chain from end nearest substituent.Cl CH3

CH3─CH2─CH─CH─CH35 4 3 2 1

STEP 3: Locate substituents and name alphabetically. 3-chloro-2-methylpentane

Learning Check

Give the IUPAC name for each of the following:

A. CH3 CH3| | CH3─CH─CH2 ─CH─CH3

B. Cl CH3| |CH3─CH2─CH─CH2─C─CH2─CH3|

Solution

A. CH3 CH3| | CH3─CH─CH2 ─CH─CH3 2,4-dimethylpentane1 2 3 4 5

B. Cl CH3 more substituents on C3| |

CH3─CH2─CH─CH2─C─CH2─CH3|Cl

7 6 5 4 3 2 1

3,5-dichloro-3-methylheptane

Guide to Drawing AlkaneFormulas

Learning Check

Draw the condensed structural formula for 3-bromo-1-chlorobutane.

Solution

3-bromo-1-chlorobutaneSTEP 1: Longest chain has 4 carbon atoms.

C─C─C─CSTEP 2: Number chain and add substituents.

C ─ C ─ C ─ C ─ Cl4 3 2 1

STEP 3: Add hydrogen to complete 4 bonds to each C.Br

CH3─CH─CH2─CH2─Cl

Naming Cycloalkanes with Substituents

The name of a substituent is placed in front of thecycloalkane name.

methylcyclobutane CH3

chlorocyclopentane Cl

Learning Check

Name each of the following.

1. CH3

CH2─CH32.

Solution

Name each of the following.

1. methylcyclopropane

2. ethylcyclohexane

10.4 Properties of Alkanes

Some Properties of Alkanes

Alkanes are• nonpolar.• insoluble in water.• less dense than water.• flammable in air.

Alkanes with 1-4 carbon atoms are

• methane, ethane, propane, and butane.

• gases at room temperature.

• used as heating fuels.

Alkanes with 5-8 carbon atoms are• liquids at room temperature.• pentane, hexane, heptane, and octane.• very volatile.• used to make gasoline.

Alkanes with 9-17 carbon atoms • are liquids at room temperature• have higher boiling points.• are found in kerosene, diesel, and jet fuels.

Alkanes with 18 or more carbon atoms• have high molar masses.• are waxy solids at room temperature.• used in waxy coatings of fruits and

vegetables.

Combustion

In combustion reactions,• alkanes react with oxygen.• CO2, H2O, and energy are produced.• Alkane + O2 CO2 + H2O + heat

Learning Check

Write a balanced equation for thecomplete combustion of propane.

Solution

Unbalanced equationC3H8 + O2 CO2 + H2O

Balance CC3H8 + O2 3CO2 + H2O

Balance HC3H8 + O2 3CO2 + 4H2O

Balance OC3H8 + 5O2 3CO2 + 4H2O (Balanced)

10.5 Functional Groups

Elements in Organic Compounds

In organic molecules, carbon atoms bond • with four bonds.• mostly with H and other C atoms.• sometimes to O, N, S. • sometimes to halogens F, Cl, and Br.

Functional groups are• a characteristic feature of organic molecules that

behave in a predictable way. • composed of an atom or group of atoms. • groups that replace a hydrogen atom in the

corresponding alkane.• a way to classify families of organic compounds.

Functional Groups

Alkenes, Alkynes, and Aromatic Compounds

Alkenes contain a double bond between adjacent carbon atoms.Alkynes contain a triple bond.Aromatic compounds contain a ring of six carbon atoms called benzene.

Comparing Alkenes, Alkynes, and Aromatic Compounds

Alcohols and Ethers

An alcohol contains the hydroxyl (-OH) functional group.

A thiol contains the thiol(-SH) functional group.

An ether contains an oxygen atom bonded to two carbon atoms.

Aldehydes and Ketones

An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom. The carbonyl is attached to a hydrogen.

In a ketone, the carbon of the carbonyl group (C=O) is attached to two carbon atoms.

Carboxylic Acids and Esters

Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group.

— C—OHAn ester contains the carboxyl group between carbon atoms.

Amines and Amides

In amines, the functional group is a nitrogen atom.

|—N —

In amides, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group.

Amines

An amide

Summary of Functional Groups

Learning Check

Classify each of the following as: alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, or amide.1) CH3─CH2─CH2─OH2) CH3─O─CH2─CH33) CH3─CH2─NH2

O O║ ║

4) CH3─C─OH 5) CH3─C─O─CH3

Solution

1) CH3─CH2─CH2─OH alcohol2) CH3─O─CH2─CH3 ether3) CH3─CH2─NH2 amine

O O║ ║

4) CH3─C─OH 5) CH3─C─O─CH3carboxylic acid ester

Chapter 10 Introduction to Organic Chemistry: Alkanes 10.1...

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