CHAPTER 10 INTRODUCTION TO ORGANIC CHEMISTRY: ALKANES

10.1 Organic Compounds

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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.

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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.

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oil (organic) and water (inorganic)

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?

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COMPARING ORGANIC AND INORGANIC COMPOUNDS

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EXAMPLES

Identify each characteristic as most typical of compounds

that 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.6

WRITING FORMULAS FOR ALKANESIn 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

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TETRAHEDRAL STRUCTURE OF CARBON

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

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ORGANIC MOLECULESIn 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─CH39

TETRAHEDRAL STRUCTURE OF CARBON

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

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CHAPTER 10 INTRODUCTION TO ORGANIC CHEMISTRY: ALKANES

10.2 Alkanes

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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 Condensed H

H C H CH4 , methane

H

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STRUCTURAL FORMULAS Condensed formulas are written for

expanded structural formula by showing each carbon and the attached hydrogen atoms.

E.g C2H6

Expanded Condensed

H H │ │ H─C ─C ─ H CH3─CH3

│ │ H H

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EXAMPLE

Write an expanded formula and condensed formula for

C4H10

NAMES OF ALKANESThe 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 15

NAMES OF ALKANESAlkanes with 5-10 carbon atoms in a chain use Greek prefixes.

Name # Carbons Structural Formula

Pentane 5 CH3CH2CH2CH2CH3

Hexane 6 CH3CH2CH2CH2CH2CH3

Heptane 7 CH3CH2CH2CH2CH2CH2CH3

Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3

Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3

Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH316

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

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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.

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=

Skeletal formula

Ball-and-stick

EXAMPLES

Write the condensed and skeletal formula for

A. ethane.

B. heptane.

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EXAMPLES

A. Write the condensed formula for:

B. What is its molecular formula?

C. What is its name?

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CYCLOALKANES

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.

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CYCLOALKANES

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

H2C

H2C CH2

H2C

H2C CH2

CH2

H2C

H2C

H2CCH2

CH2

CH2

Condensed formula

Skeletal formula

10.3 ALKANES WITH SUBSTITUENTS

Isomers of Butanehave the same

molecular formula.• have different atom

arrangements.

• of butane (C4H10) are a straight chain and a branched chain.

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H3CCH2

H2C

CH3

H3CCH

CH3

CH3

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

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ALKANES WITH SUBSTITUENTS

CH3

CH3 CH CH3 methylpropane

methyl groups

CH3 CH3

CH3 CH CH2 CH CH3

2,4-dimethylpentane25

NAMING SUBSTITUENTS

In the IUPAC system,• a carbon branch is

named as an alkyl group.

• halogen atoms are named as halo.

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NAMING HALO-ALKANES

Step 1: determine the long chain Name it as parent chain

Step 2: identify substituents Akyl – all CH Halo – halogen

Chlorine Chloro Bromine bromo

number carbon starting from the end closet to the substituent

Step 3: name the molecule in alphabetical order. Location-substituentparent chain

NAMING ALKANESGive the name of CH3 CH3

CH3─CH─CH─CH3

STEP 1: Name the longest continuous chain.

STEP 2: Number chain.

STEP 3: Locate substituents and name. 28

EXAMPLE

Name the following molecules

Cl

Br

EXAMPLE

Write the name of

Cl CH3

CH3─CH2─CH─CH─CH3

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LEARNING CHECKGive 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

|

Cl31

LEARNING CHECKDraw the condensed structural formula for 3-bromo-1-chlorobutane.

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STEP 1: Longest chain has 4 carbon atoms.

STEP 2: Number chain and add substituents.

TEP 3: Add hydrogen to complete 4 bonds to each C.

NAMING CYCLOALKANES WITH SUBSTITUENTS

The name of a substituent is placed in front of the

cycloalkane name. CH3

methylcyclobutane

Cl

Chlorocyclopentane

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LEARNING CHECK

Name each of the following.

1. CH3

CH2─CH3

2.

3.34

F

EXAMPLESName the following.

A. CH3─CH2─CH2─CH3

B.

C.

D.35

H3CCH2

CHCH2

H2C

CH2

CH3

10.4 PROPERTIES OF ALKANES

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

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SOME PROPERTIES OF ALKANES

Alkanes with 1-4 carbon atoms are

• methane, ethane, propane, and butane.

• gases at room temperature.

• used as heating fuels.

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SOME PROPERTIES OF ALKANES

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.38

SOME PROPERTIES OF ALKANES

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.

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COMBUSTION

In combustion reactions,

• alkanes react with oxygen.

• CO2, H2O, and energy are produced.

• Alkane + O2 CO2 + H2O + heat

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LEARNING CHECK

Write a balanced equation for thecomplete combustion of a. Propane

b. Octane

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10.5 FUNCTIONAL GROUPS

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.

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FUNCTIONAL GROUPS

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.

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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.

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C C C C

alkene alkynearomatic

H

H

H

HH H

H

H

H

H

H

H

COMPARING ALKENES, ALKYNES, AND AROMATIC COMPOUNDS

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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.

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R OH

Alcohol

R SH

thiol

R O R

ether

R = alkyl groups (carbon groups)

ALDEHYDES AND KETONESAn 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.

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RC

O

HAldehyde

RC

O

RKetone

CARBOXYLIC ACIDS AND ESTERS

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

O ║

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

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RC

O

OH

carboxylic

RC

O

O

ester

R

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.

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Amines

An amide

SUMMARY OF FUNCTIONAL GROUPS

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LEARNING CHECK

Classify each of the following as: alcohol, ether, aldehyde, ketone, carboxylic acid, ester, amine, or amide.

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O OH

HO

OO

O