Chapter 11 Introduction to Organic Chemistry: Alkanes

Chapter 11 Introduction to Organic Chemistry: Alkanes 11.1 Organic Compounds Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 1

Organic Compounds 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. 2

Properties of Organic Compounds Typical organic compounds Contain carbon. Have covalent bonds. Have low melting points. Have low boiling points. Are flammable. Are soluble in nonpolar solvents. Are not soluble in water. Oil (organic) and water (inorganic) Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 3

Organic vs. Inorganic Propane, C 3 H 8, is an organic compound used as a fuel. NaCl, salt, is an inorganic compound composed of Na + and Cl ions. Why is propane an organic compound, but NaCl is not? Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 4

Comparing Organic and Inorganic Compounds TABLE 11.1 Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 5

Learning Check Identify each characteristic as most typical of compounds that are (I) inorganic or (O) organic. 1. Has a high melting point 2. Is not soluble in water 3. Has a formula CH 3 CH 2 CH 3 4. Has a formula MgCl 2 5. Burns easily in air 6. Has covalent bonds 6

Solution Identify each characteristic as most typical of compounds that are (I) inorganic or (O) organic. I 1. Has a high melting point O 2. Is not soluble in water O 3. Has a formula CH 3 CH 2 CH 3 I 4. Has a formula MgCl 2 O 5. Burns easily in air O 6. Has covalent bonds 7

Writing Formulas for Carbon Compounds In carbon compounds Carbon has 4 valence electrons and hydrogen has 1. C H To achieve an octet, C forms four bonds. H H H : C : H H C H H H CH 4, methane 8

Tetrahedral Structure of Carbon VSEPR theory predicts that a carbon atom with four single, covalent bonds has a tetrahedral shape. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 9

Organic Compounds with More Carbon Atoms In organic molecules with more carbon atoms, Valence electrons are shared. Covalent bonds form between carbon and carbon atoms. Covalent bonds form between carbon and hydrogen atoms. H H H H H : C : C : H H C C H H H H H ethane, CH 3 CH 3 10

Tetrahedral Structure of Carbon In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 11

Chapter 11 Introduction to Organic Chemistry: Alkanes 11.2 Alkanes Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 12

Names of Alkanes The names of alkanes Are determined by the IUPAC (International Union of Pure and Applied Chemistry) system. Use a prefix to indicate the number of carbons in a chain. End in ane. 13

IUPAC Names for Alkanes TABLE 11.2 Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 14

Learning Check A. Give the name of each compound: 1) CH 3 CH 3 2) CH 3 CH 2 CH 3 3) CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 B. Write the condensed structural formula of pentane. 15

Solution A. Give the name of each compound: 1) CH 3 CH 3 ethane 2) CH 3 CH 2 CH 3 propane 3) CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 hexane B. Write the condensed structural formula of pentane. CH 3 CH 2 CH 2 CH 2 CH 3 16

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 CH 4, methane H 17

Writing Structural Formulas Carbon atoms in a chain Maintain tetrahedral shape. Are connected in a zig-zag pattern. Are drawn as 2-dimensional. Can be written in several conformations. 18

Expanded and Condensed Structures TABLE 11.3 Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 19

Line-Bond Formulas Because each C atom has a tetrahedral arrangement, the order of atoms is not a straight line, but a zigzag pattern. A line-bond formula abbreviates the carbon atoms and shows only the zigzag pattern of bonds from carbon atom to carbon atom. 20

Conformations The groups attached to a C-C single bond Rotate around the bond, Give different relative arrangements called conformations. 21 Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Conformations of Butane Rotation of the end CH 3 - provides different conformations for butane. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cumming 22

Some Structures for Butane TABLE 11.3 Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 23

Hexane has Six Carbon Atoms Hexane Is an alkane with 6 carbon atoms in a continuous chain. Has a zig-zag look because each carbon atom is at the center of a tetrahedron. Is represented by a ball-and-stick model as Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 24

Learning Check A. Write the condensed formula for: H H H H H H C C C C C H H H H H H B. What is its molecular formula? C. What is its name? 25

Solution A. CH 3 CH 2 CH 2 CH 2 CH 3 B. C 5 H 12 C. pentane 26

Learning Check Write the condensed structural formula for A. ethane B. heptane 27

Solution Write the condensed structural formula for A. ethane CH 3 CH 3 B. heptane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 28

Cycloalkanes Cycloalkanes Are cyclic alkanes. Have 2H 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. 29

Cycloalkanes The structural formulas of cycloalkanes are usually represented by geometric figures, Cyclopropane CH 2 CH 2 CH 2 Cyclobutane CH 2 CH 2 CH 2 CH 2 30

More Cycloalkanes Cyclopentane CH 2 CH 2 CH 2 Cyclohexane CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 31

Learning Check Name the following: A. CH 3 CH 2 CH 2 CH 3 B. C. CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 D. 32

Solution Name the following: A. CH 3 CH 2 CH 2 CH 3 butane B. cyclopropane C. CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 octane D. cyclohexane 33

Chapter 11 Introduction to Organic Chemistry: Alkanes 11.4 Properties of Alkanes Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 34

Some Properties of Alkanes The properties of alkanes include being Nonpolar. Insoluble in water. Less dense than water Flammable in air. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 35

Alkanes with 1-4 Carbon Atoms Alkanes with 1-4 carbon atoms are Methane, ethane, propane, and butane. Gases at room temperature. Used as heating fuels. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 36

Alkanes with 5-17 Carbon Atoms 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. 37

Alkanes with 18 or more Carbon Atoms 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. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 38

Boiling Points of Pentanes Boiling points of alkanes Are lowest of organic compounds. Increase with larger molecules due to increased dispersion forces. Decrease for branched alkanes. Increase for cycloalkanes. TABLE 11.6 39

Learning Check For the following pairs of hydrocarbon, which one has the higher boiling point? Why? 1. butane or octane 2. hexane or 2,3-dimethylbutane 40

Solution For the following pairs of hydrocarbon, which one has the higher boiling point? Why? 1. butane or octane octane has more carbon atoms 2. hexane or 2,3-dimethylbutane hexane is not branched 41

Crude Oil The hydrocarbons in crude oil are Separated by boiling points. Heated to higher temperatures to produce gases that can be removed and cooled. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 42

Classification of Carbon Atoms The classification of carbon atoms indicates the number of carbon atoms attached. A primary carbon (1 ) bonds to one carbon atom. A secondary carbon (2 ) bonds to two carbon atoms. A tertiary carbon (3 ) bonds to three carbon atoms. CH 3 CH 3 CH 2 CH 2 CH 3 CH 3 CH CH 3 primary secondary tertiary 43

Combustion of Alkanes Alkanes Undergo combustion by reacting with oxygen to produce carbon dioxide, water, and energy. Are typically not very reactive due to strong C-C single bonds. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings alkane + O 2 CO 2 + H 2 O + energy 44

Balancing A Combustion Equation Write the equation C 5 H 12 + O 2 Balance C C 5 H 12 + O 2 Balance H C 5 H 12 + O 2 Balance O with O 2 C 5 H 12 + 8O 2 CO 2 + H 2 O 5CO 2 + H 2 O 5CO 2 + 6H 2 O 5CO 2 + 6H 2 O balanced 45

Learning Check Propane is used to provide heat for cooking or warming a room. Write a balanced equation for the complete combustion of propane. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 46

Solution Unbalanced equation C 3 H 8 + O 2 Balance C C 3 H 8 + O 2 Balance H C 3 H 8 + O 2 Balance O C 3 H 8 + 5O 2 CO 2 + H 2 O 3CO 2 + H 2 O 3CO 2 + 4H 2 O 3CO 2 + 4H 2 O (Balanced) 47

Learning Check Write a balanced equation for the reaction for the complete combustion of heptane C 7 H 16. 48

Solution C 7 H 16 + O 2 C 7 H 16 + O 2 C 7 H 16 + O 2 C 7 H 16 +11O 2 CO 2 + H 2 O 7CO 2 + 8H 2 O 7CO 2 + 8H 2 O 7CO 2 + 8H 2 O Balanced equation: C 7 H 16 + 11O 2 7CO 2 + 8H 2 O 49

Learning Check Write the combustion reaction for ethane and balance. 50

Solution Write the combustion reaction for ethane and balance. ethane CH 3 CH 3 = C 2 H 6 C 2 H 6 + O 2 2CO 2 + 3H 2 O C 2 H 6 + 7 O 2 2CO 2 + 3H 2 O C 2 H 6 + 7/2 O 2 2CO 2 + 3H 2 O Multiply through by 2 to clear 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O balanced 51

Halogenation of Alkanes (Substitution) When alkanes react with halogens, The reaction is called substitution, one or more H atoms are replaced with a halogen usually Cl or Br. Light or heat is required. A mixture of halogenated products result, but we write the equation with the monosubstituted product. Example: ethane and chloride light CH 3 CH 3 + Cl 2 CH 3 CH 2 Cl 52

Learning Check Give the structures and names of the possible monosubstituted products for the reaction of propane with bromine in the presence of light. 53

Solution Give the structures and names of the possible monosubstituted products for the reaction of propane with bromine in the presence of light. CH 3 CH 2 CH 2 Br Br 1-bromopropane; propyl bromide CH 3 CH CH 3 2-bromopropane; isopropyl bromide 54

Chapter 11 Introduction to Organic Chemistry: Alkanes 11.3 Alkanes with Substituents Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 55

Isomers of Butane Isomers Have the same molecular formula. Have different atom arrangements. Of butane (C 4 H 10 ) consist of a straight chain and a branched chain each with 4 carbon atoms. branch Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 56

Alkyl groups Alkyl groups are Alkanes that are missing one H. Substituents attached to carbon chains. Named with a yl ending. H H C CH 3 methyl H H H H C C CH 3 CH 2 ethyl H H 57

Naming Substituents In the IUPAC system, A carbon branch is named as an alkyl group. Halogen atoms are named as halo. TABLE 11.5 Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 58

Alkanes with Alkyl Groups CH 3 CH 3 CH CH 3 methylpropane methyl groups CH 3 CH 3 CH 3 CH CH 2 CH CH 3 2,4-dimethylpentane 59

Naming Alkanes with Substituents Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 60

Guide to Naming Alkanes Give the name of CH 3 CH 3 CH 3 CH CH CH 3 STEP 1 Longest chain is butane. STEP 2 Number chain. CH CH 3 3 CH 3 CH CH CH 3 1 2 3 4 STEP 3 Locate substituents and name. 2,3-dimethylbutane 61

Learning Check Write the IUPAC name for Cl CH 3 CH 3 CH 2 CH CH CH 3 62

Solution STEP 1 STEP 2 Longest chain is pentane. Number chain from end nearest substituent. Cl CH 3 (nearest end) CH 3 CH 2 CH CH CH 3 5 4 3 2 1 STEP 3 Locate substituents and name alphabetically. 3-chloro-2-methylpentane 63

Learning Check Give the IUPAC name for each of the following: A. CH 3 CH 3 CH 3 CH CH 2 CH CH 2 CH 3 B. Cl CH 3 CH 3 CH 2 CH CH 2 C CH 2 CH 3 Cl 64

Solution A. CH 3 CH 3 CH 3 CH CH 2 CH CH 2 CH 3 2,4-dimethylhexane 1 2 3 4 5 6 B. Cl CH 3 more substituents on C3 CH 3 CH 2 CH CH 2 C CH 2 CH 3 Cl 7 6 5 4 3 2 1 3,5-dichloro-3-methylheptane 65

Drawing Alkane Structures Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 66

What is In A Name? The structural formula is drawn from the IUPAC name. 2, 4-dimethylhexane 2, 4 dimethyl hexane Location of Two CH 3 - groups 6 carbon main chain branches on attached with single C-C bonds main chain 67

Learning Check Draw the condensed structural formula for 2-bromo-4-chlorobutane. 68

Solution STEP 1 Longest chain has 4 carbon atoms. C C C C STEP 2 Number chain and add substituents. Br C C C C Cl 1 2 3 4 STEP 3 Add hydrogen to complete 4 bonds to each C. Br CH 3 CH CH 2 CH 2 Cl 69

Naming Cycloalkanes with Substituents The name of a substituent is placed in front of the cycloalkane name. methylcyclobutane CH 3 Number ring with two substituents 1-bromo-2-chlorocyclopentane Br Cl 70

Learning Check Name each of the following: 1. CH 3 2. CH 2 CH 3 Cl 71

Solution Name each of the following: 1. methylcyclopropane 2. 3-chloro-1-ethylcyclohexane 72

Learning Check Write three isomers of C 5 H 12 and name each. 73

Solution A chain of 5 carbon atoms CH 3 CH 2 CH 2 CH 2 CH 3 pentane A chain of 4 carbon atoms and 1 carbon branch CH 3 CH 3 CH CH 2 CH 3 2-methylbutane A chain of 3 carbon atoms and 2 carbon branches CH 3 CH 3 CH CH 3 2,2-dimethylpropane CH 3 74