22 1 Hydrocarbons Chapter 22 Hydrocarbon Compounds 22

22. 1 Hydrocarbons > Chapter 22 Hydrocarbon Compounds 22. 1 Hydrocarbons 22. 2 Unsaturated Hydrocarbons 22. 3 Isomers 22. 4 Hydrocarbon Rings 22. 5 Hydrocarbons from Earth’s Crust 1 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > CHEMISTRY & YOU Why are some fossil fuels gases, some liquids, and some solids? The gasoline used to fuel this motorcycle and other fuels contain mixtures of compounds called hydrocarbons. 2 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons Why does a carbon atom form

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons • Fewer than 200 years ago, it was thought that only living organisms could synthesize the carbon compounds found in their cells. • So, these compounds were classified as organic compounds, and the study of these compounds was known as organic chemistry. 4 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons • German chemist Friedrich Wöhler refuted this idea in 1828. • He was able to use inorganic substances to synthesize urea—an organic compound found in urine. • Today, organic chemistry includes the chemistry of almost all carbon compounds, regardless of their origin. 5 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons Introduction to Hydrocarbons • The simplest organic compounds are called hydrocarbons. • A hydrocarbon is an organic compound that contains only carbon and hydrogen. • The two simplest hydrocarbons are methane and ethane. • Methane (CH 4) is the major component of natural gas. 6 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons Introduction to Hydrocarbons • Recall that a carbon atom has four valence electrons and a hydrogen atom has one valence electron. • So, one carbon atom can form a single covalent bond with four hydrogen atoms as shown: 7 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons Introduction to Hydrocarbons • Because carbon has four valence electrons, a carbon atom always forms four covalent bonds. • Methane is not typical of the vast majority of organic compounds because there isn’t a bond between carbon atoms in a methane molecule. 8 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons Introduction to Hydrocarbons • There is a carbon-carbon bond in ethane. • The ability of carbon to form stable carbon bonds is one reason that carbon can form so many different compounds. 9 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons Representing Hydrocarbons The table below shows the structural formulas, ball-and-stick models, and space-filling models for methane and ethane. Different Ways of Representing Hydrocarbons Name Structural formula Ball-and-stick model Space-filling model Methane Ethane 10 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons Properties of Hydrocarbons • The electron pair in a carbon-hydrogen or a carbon-carbon bond is shared almost equally by the nuclei of the atoms forming the bond. • Thus, hydrocarbons are nonpolar molecules. • The attractions between nonpolar molecules are weak van der Waals forces. • So, hydrocarbons with low molar masses tend to be gases or liquids that boil at a low temperature. 11 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Organic Chemistry and Hydrocarbons Properties of Hydrocarbons Recall the general rule “like dissolves like. ” • A nonpolar compound a polar compound will not form a solution. • For example, because oil is a mixture of hydrocarbons, oil and water do not mix. 12 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > What types of compounds are included in the study of organic chemistry? Organic chemistry includes the chemistry of almost all carbon compounds, regardless of whether they are synthesized by living organisms or from inorganic substances. 14 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes What are two possible arrangements of carbon atoms in

22. 1 Hydrocarbons > Alkanes • Methane and ethane are examples of alkanes. • An alkane is a hydrocarbon in which there are only single covalent bonds. • The carbon atoms in an alkane can be arranged in a straight chain or in a chain that has branches. 16 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes • Ethane is the simplest straight-chain alkane, which is an alkane that contains any number of carbon atoms, one after the other, in a chain. • Propane (C 3 H 8) has three carbon atoms. • Butane (C 4 H 10) has a chain of four carbons. 17 Propane Butane Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Interpret Graphs Straight-Chain Alkanes 18 200 Temperature ( C) This graph illustrates how the melting and boiling points vary with the number of carbons in straight-chain alkanes. Melting and Boiling Points Of Straight-Chain Alkanes 100 0 – 100 – 200 0 2 4 6 8 Number of carbons Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved. 10

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes • The straight-chain alkanes are an example of a homologous series. • A group of compounds forms a homologous series if there is a constant increment of change in molecular structure from one compound in the series to the next. • A CH 2 group is the increment of change in straight-chain alkanes. 19 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes The constant increment of change within the alkanes is summarized below. Ethane (C 2 H 6) Propane (C 3 H 8) 20 Increment of change Propane (C 3 H 8) Butane (C 4 H 10) Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes • The names of the straight-chain alkanes follow rules established by the International Union of Pure and Applied Chemistry (IUPAC). • Every alkane has a name that ends with the suffix -ane. 21 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes • For the straight-chain alkanes with one to four carbon atoms, the official names and the common names are the same. Straight-Chain Alkanes Name • For the chains longer than 4, the prefixes are pent- for 5, hex- for 6, hept- for 7, oct- for 8, non- for 9, and dec- for 10. 22 Formula Methane CH 4 Ethane C 2 H 6 Propane C 4 H 8 Butane C 4 H 10 Pentane C 5 H 12 Hexane C 6 H 14 Heptane C 7 H 16 Octane C 8 H 18 Nonane C 9 H 20 Decane C 10 H 22 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > CHEMISTRY & YOU You just learned that the boiling and melting points of straight-chain alkanes increase as the number of carbons increase. Now explain why some hydrocarbon fuels are gases and others are liquids. 23 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > CHEMISTRY & YOU You just learned that the boiling and melting points of straight-chain alkanes increase as the number of carbons increase. Now explain why some hydrocarbon fuels are gases and others are liquids. Straight-chain alkanes with fewer carbons have lower boiling and melting points than those with more carbons in their chains. Alkanes with shorter chains are gases at STP; alkanes with longer chains are liquids at STP. 24 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes • To draw the structural formula for a straightchain alkane, write the symbol for carbon as many times as necessary to get the proper chain length. • Then complete the formula with hydrogens and lines representing covalent bonds. 25 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes • Complete structural formulas show all the atoms and bonds in a molecule. • Sometimes, however, shorthand or condensed structural formulas work just as well. • In a condensed structural formula, some bonds and/or atoms are left out of the structural formula. • Although the bonds and atoms do not appear, you must understand that they are there. 26 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes • A condensed structural formula in the form of CH 3(CH 2)n. CH 3 uses a different kind of shorthand. • The CH 2 unit in parentheses is called a methylene group. • The subscript n to the right of the parentheses indicates the number of methylene groups that are linked together. 27 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Straight-Chain Alkanes • This shorthand method applies to butane as follows: • The subscript after the parentheses in the condensed structural formula for butane is 2. • This means two methylene groups are linked together in the structure. 28 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Formulas for Butane There are several ways to draw condensed structural formulas. Formula Description C 4 H 10 Molecular formula Complete structural formula CH 3–CH 2–CH 3 CH 2 CH 3(CH 2)2 CH 3 C–C–C–C Condensed structural formula (C–H bonds understood) Condensed structural formula (C–H and C–C bonds understood) Condensed structural formula (all bonds understood) Carbon skeleton (hydrogens and C–H bonds understood) Line-angle formula (carbons and hydrogens understood) 29 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 1 Drawing Structural Formulas for Alkanes Draw complete structural formulas for the straight-chain alkanes that have a. three carbon atoms. b. four carbon atoms. 30 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 1 1 Analyze Identify the relevant concepts. In an alkane, each carbon atom forms four covalent bonds to hydrogen or to other carbon atoms. Because these are straight-chain alkanes, write the appropriate number of carbons in a straight line, connected to each other by single bonds. Then add the appropriate number of hydrogen atoms. 31 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 1 2 Solve Apply the concepts to this problem. Start with the number of carbons. a. b. 32 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 1 2 Solve Apply the concepts to this problem. Each center carbon bonds to two hydrogens. Each end carbon bonds to three hydrogens. a. b. Make sure each carbon has 4 bonds. 33 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes • Because a carbon atom forms four covalent bonds, it can bond not only to one or two other carbon atoms, but also to three or even four other carbons, resulting in branched chains. • In organic chemistry, branches on a hydrocarbon chain are discussed as if they were substituted for a hydrogen atom on the chain. • An atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule is called a substituent. 34 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes • The longest continuous carbon chain of a branched-chain hydrocarbon is called the parent alkane. • All other carbon atoms or groups of carbon atoms are regarded as substituents. • Atoms such as halogens, oxygen, and nitrogen can also be substituents. 35 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes • A hydrocarbon substituent that is derived from an alkane is called an alkyl group. • You can think of any alkyl group as just an alkane with one of the hydrogens removed. • Alkyl groups are named by removing the -ane ending from the parent hydrocarbon name and adding -yl. 36 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes • The three smallest alkyl groups are • the methyl group (–CH 3) • the ethyl group (–CH 2 CH 3) • the propyl group (–CH 2 CH 3) • When a substituent alkyl group is attached to a straight-chain hydrocarbon, branches are formed. • An alkane with one or more alkyl groups is called a branched-chain alkane. 37 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes • Each carbon in an organic molecule can be categorized as a primary, secondary, tertiary, or quaternary carbon. • If the carbon in question has only one carbon attached to it, then the carbon is a primary carbon. • If two carbons are attached to the carbon in question, the carbon is a secondary carbon; if three carbons, a tertiary carbon; and if four carbons, a quaternary carbon. 38 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes Examples of primary, secondary, tertiary, and quaternary carbons are labeled in the structural formulas below. 39 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes • Isooctane is a hydrocarbon that contains each of these types of carbons. • Isooctane is the standard for determining octane ratings of the mixtures of hydrocarbons that make up gasoline. 40 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes • The IUPAC rules for naming branchedchain alkanes are quite straightforward. • The name of the branched-chain alkane is based on the name of the longest continuous carbon chain. • Each substituent is named according to the length of its chain and numbered according to its position on the main chain. 41 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes The compound with the following structural formula can be used as an example. 42 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes 1. Find the longest continuous chain of carbons in the molecule. This chain is considered the parent hydrocarbon. • The longest chain is highlighted in the example. It contains seven carbon atoms. So, the parent hydrocarbon is heptane. 43 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes 2. Number the carbons in the main chain in sequence. To do this, start at the end that will give the substituent groups attached to the chain the smallest numbers. • Numbering the chain from right to left gives the substituents the lowest numbers (2, 3, and 4). 44 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes 3. Add numbers to the names of the substituent groups to identify their positions on the chain. These numbers become prefixes to the name of the substituent group. • The substituents and positions are 2 -methyl, 3 -methyl, and 4 -ethyl. 45 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes 4. Use prefixes to indicate the appearance of the same group more than once in the structural formula. Common prefixes are di- (twice), tri(three times), and tetra- (four times). • The two methyl groups are combined as 2, 3 dimethyl in the name. 46 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes 5. List the names of alkyl substituents in alphabetical order. For purposes of alphabetizing, ignore the prefixes di-, tri-, and so on. • The 4 -ethyl group is listed first, followed by the 2, 3 -dimethyl. 47 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes Branched-Chain Alkanes 6. Combine all the parts and use proper punctuation. Write the entire name without any spaces. Use commas to separate numbers, and use hyphens to separate numbers and words. • The correct name of the compound is 4 -ethyl 2, 3 -dimethylheptane. 48 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 2 Naming Branched-Chain Alkanes Name this compound using the IUPAC system. Notice that the longest chain is not written in a straight line. 49 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 2 1 Analyze Identify the relevant concepts. The parent structure is the longest chain of carbons. All other groups are substituents. Number the carbons to give the first substituent the lowest possible number. These location numbers become part of the name as prefixes. List the names of the substituents in alphabetical order with numbers separated by commas, and numbers and words separated by hyphens. 50 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 2 2 Solve Apply the concepts to this problem. Identify the longest carbon chain in the molecule. • The longest chain has six carbons, so the name ends with hexane. 51 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 2 2 Solve Apply the concepts to this problem. Identify the substituents and their positions on the parent hydrocarbon. • There are two methyl substituents on carbon 3, so the prefix is 3, 3 Remember to start numbering at dimethyl. the end that gives the substituents the smallest numbers! 52 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 2 2 Solve Apply the concepts to this problem. Put everything together. You can skip the alphabetizing step because there is only one type of substituent. • The correct IUPAC name is 3, 3 dimethylhexane. 53 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Alkanes With the name of a branched-chain alkane and knowledge of IUPAC rules, it is easy to reconstruct the structural formula. 1. Find the root word (ending in -ane) in the hydrocarbon name. 2. Then, draw the longest carbon chain to create the parent hydrocarbon, and number the carbons in the chain. 3. Identify the substituent groups in the hydrocarbon name. Attach the substituents to the numbered parent chain at the proper positions. 4. Complete the structural formula by adding hydrogens as needed. 54 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 3 Drawing Structural Formulas for Branched-Chain Alkanes Draw the structural formula for 2, 2, 4 -trimethylpentane, or isooctane. 55 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 3 1 Analyze Identify the relevant concepts. Draw the structural formula for 2, 2, 4 -trimethylpentane. The part of the name that ends in -ane indicates the parent structure. Prefixes indicate the types of substituents, the number of times each appears, and their locations on the parent chain. Hydrogens are added as needed. 56 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 3 2 Solve Apply the concepts to this problem. Draw the structural formula for 2, 2, 4 -trimethylpentane. Draw the number of carbons needed to represent the parent structure indicated in the name, and number the carbons on the chain. • 57 The parent structure is pentane, which has five carbon atoms. Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 3 2 Solve Apply the concepts to this problem. Draw the structural formula for 2, 2, 4 -trimethylpentane. Attach each substituent as indicated in the prefix. • 58 There are two methyl groups on carbon 2 and one on carbon 4. Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Sample Problem 22. 3 2 Solve Apply the concepts to this problem. Draw the structural formula for 2, 2, 4 -trimethylpentane. Finish by adding hydrogens where needed in the formula. • A total of nine hydrogens need to be added to complete the structure. Be careful: Each carbon has four, and only four, bonds. 59 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > What is the difference between a straightchain alkane and a branched-chain alkane? A straight-chain alkane contains any number of carbon atoms bonded in a chain. Its carbon atoms are bonded to either one or two other carbons. A branched-chain alkane can have one or more alkyl groups attached to it. Its carbon atoms can be bonded to one, two, three, or four other carbons. 61 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Key Concepts Because carbon has four valence electrons, a carbon atom always forms four covalent bonds. The carbon atoms in an alkane can be arranged in a straight chain that has branches. 62 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Glossary Terms • hydrocarbon: an organic compound that contains only carbon and hydrogen • alkane: a hydrocarbon containing only single covalent bonds; alkanes are saturated hydrocarbons • straight-chain alkane: a saturated hydrocarbon that contains any number of carbon atoms arranged one after the other in a chain 63 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Glossary Terms • homologous series: a group of compounds in which there is a constant increment of change in molecular structure from one compound in the series to the next • condensed structural formula: a structural formula that leaves out some bonds and/or atoms; the presence of these atoms or bonds is understood 64 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > Glossary Terms • substituent: an atom or group of atoms that can take the place of a hydrogen atom on a parent hydrocarbon molecule • alkyl group: a hydrocarbon substituent; the methyl group (–CH 3) is an alkyl group • branched-chain alkane: an alkane with one or more alkyl groups attached to the parent structure 65 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

22. 1 Hydrocarbons > BIG IDEA • Organic compounds are named using the IUPAC system, although sometimes common names are used for certain familiar compounds. • All hydrocarbons are nonpolar molecules. • In general, the fewer carbon atoms in a hydrocarbon, the lower its melting and boiling points. 66 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.