Organic Chemistry A UNIT 1 CONTENTS t this moment, you are walking, CHAPTER 1 sitting, or standing in an “organic” Classifying Organic Compounds body. Your skin, hair, muscles, heart, CHAPTER 2 and lungs are all made from organic Reactions of Organic Compounds compounds. In fact, the only parts of your body that are notmostly organic UNIT 1 ISSUE are your teeth and bones! When you Current Issues Related to study organic chemistry, you are Organic Chemistry studying the substances that make up your body and much of the world UNIT 1 OVERALL EXPECTATIONS around you. Medicines, clothing, carpets, curtains, and wood and How do the structures of plastic furniture are all manufactured various organic compounds differ? What chemical from organic chemicals. If you look reactions are typical of these out a window, the grass, trees, squir- compounds? rels, and insects you may see are also How can you name different composed of organic compounds. organic compounds and Are you having a sandwich for represent their structures? lunch? Bread, butter, meat, and lettuce What do you need to know in are made from organic compounds. order to predict the products Will you have dessert? Sugar, flour, of organic reactions? vanilla, and chocolate are also organic. How do organic compounds What about a drink? Milk and juice affect your life? How do they are solutions of water in which affect the environment? organic compounds are dissolved. In this unit, you will study a variety of organic compounds. You Unit Issue Prep will learn how to name them and how Before beginning Unit 1, read to draw their structures. You will also pages 110 to 111 to find out about learn how these compounds react, and the unit issue. In the unit issue, you you will use your knowledge to pre- will analyze an issue that involves dict the products of organic reactions. chemistry and society. You can In addition, you will discover the start planning your research as you amazing variety of organic compounds go through this unit. Which topics interest you the most? How does in your body and in your life. society influence developments in science and technology? 2 Classifying Organic Compounds A Chapter Preview s you wander through the supermarket, some advertising claims catch your eye. “Certified organic” and “all natural” are stamped on the labels 1.1 Bonding and the Shape of some foods. Other labels claim that the foods are “chemical free.” As a of Organic Molecules chemistry student, you are aware that these labels may be misleading. Are 1.2 Hydrocarbons all “chemicals” harmful in food, as some of the current advertising suggests? 1.3 Single-Bonded Many terms are used inaccurately in everyday life. The word “natural” Functional Groups is often used in a manner suggesting that all natural compounds are safe 1.4 Functional Groups and healthy. Similarly, the word “chemical” is commonly used to refer to With the C(cid:2)O bond artificial compounds only. The food industry uses “organic” to indicate foods that have been grown without the use of pesticides, herbicides, fertilizers, hormones, and other synthetic chemicals. The original meaning of the word “organic” refers to anything that is or has been alive. In this sense, all vegetables are organic, no matter how they are grown. Organic chemistry is the study of compounds that are based on carbon. Natural gas, rubbing alcohol, aspirin, and the compounds that give fragrance to a rose, are all organic compounds. In this chapter, you will learn how to identify and name molecules from the basic families of organic compounds. You will be introduced to the shape, structure, and Prerequisite Concepts and Skills properties of different types of organic compounds. Before you begin this chapter, review the following concepts What is the word “organic” intended to mean here? and skills: How is this meaning different from the scientific (cid:2) drawing Lewis structures meaning of the word? (Concepts and Skills Review) (cid:2) writing molecular formulas and expanded molecular formulas (Concepts and Skills Review) (cid:2) drawing complete, con- densed, and line structural diagrams (Concepts and Skills Review) (cid:2) identifying structural isomers (Concepts and Skills Review) 4 MHR • Unit 1 Organic Chemistry Bonding and the 1.1 Shape of Organic Molecules Early scientists defined organic compounds as compounds that originate Section Preview/ from living things. In 1828, however, the German chemist Friedrich Wohler Specific Expectations (1800–1882) made an organic compound called urea, CO(NH2)2, out of an In this section, you will inorganic compound called ammonium cyanate, NH CN. Urea is found in 4 (cid:2) discussthe use of the the urine of mammals. This was the first time in history that a compound terms organic, natural, and normally made only by living things was made from a non-living sub- chemicalin advertising stance. Since Wohler had discovered that organic compounds can be made (cid:2) demonstratean under- without the involvement of a life process, a new definition was required. standing of the three types Organic compoundsare now defined as compounds that are based on of carbon-carbon bonding carbon. They usually contain carbon-carbon and carbon-hydrogen bonds. and the shape of a molecule around each type of bond The Carbon Atom (cid:2) communicateyour under- standing of the following There are several million organic compounds, but only about a quarter terms: organic chemistry, of a million inorganic compounds (compounds that are not based on organic compounds, carbon). Why are there so many organic compounds? The answer lies in tetrahedral, trigonal the bonding properties of carbon. planar,linear,bent, As shown in Figure 1.1, each carbon atom usually forms a total of electronegativity,bond dipole, polar, molecular four covalent bonds. Thus, a carbon atom can connect to as many as four polarity other atoms. Carbon can bond to many other types of atoms, including hydrogen, oxygen, and nitrogen. H • •• Web LINK + → C • 4H • H • C • H • • • www.mcgrawhill.ca/links/ • •• H chemistry12 In the chapter opener, you Figure 1.1 This Lewis structure shows methane, the simplest organic compound. The considered how the terms carbon atom has four valence electrons, and it obtains four more electrons by forming four “natural” and “chemical” are covalent bonds with the four hydrogen atoms. used inaccurately. A natural substance is a substance that In addition, carbon atoms can form strong single, double, or triple bonds occurs in nature and is not with other carbon atoms. In a single carbon-carbon bond, one pair of artificial. A chemicalis any electrons is shared between two carbon atoms. In a double bond, two substance that has been made pairs of electrons are shared between two atoms. In a triple bond, three using chemical processes in a laboratory. A chemical can pairs of electrons are shared between two atoms. also be defined as any sub- Molecules that contain only single carbon-carbon bonds are saturated. stance that is composed of In other words, all carbon atoms are bonded to the maximum number of atoms. This definition covers other atoms: four. No more bonding can occur. Molecules that contain most things on Earth. Go to the double or triple carbon-carbon bonds are unsaturated. The carbon atoms web site above, and click on on either side of the double or triple bond are bonded to less than four Web Linksto find out where atoms each. There is potential for more atoms to bond to each of these to go next. Look up some carbon atoms. naturalpoisons, pesticides, and antibiotics that are Carbon’s unique bonding properties allow the formation of a produced by animals, plants, variety of structures, including chains and rings of many shapes and and bacteria. Then look up sizes. Figure 1.2 on the next page illustrates some of the many shapes some beneficial chemicals that can be formed from a backbone of carbon atoms. This figure includes that have been synthesized examples of three types of structural diagrams that are used to depict by humans. Make a poster to organic molecules. (The Concepts and Skills Review contains a further illustrate your findings. review of these types of structural diagrams.) Chapter 1 Classifying Organic Compounds • MHR 5 CHEM A H B C FACT H C H A few carbon compounds are considered to be inorganic. H C H These include carbon dioxide, C C CH C CH 3 CO , and and carbon com- 2 pounds containing complex C C H C H negative ions (for example, CO2−, HCO−, and OCN−). 3 3 H C H H Figure 1.2 (A) This complete structural diagram shows all the bonds in the molecule. (B) This condensed structural diagram shows only carbon-carbon bonds. (C) This line structural diagram uses lines to depict carbon-carbon bonds. Carbon compounds in which carbon forms only single bonds have a different shape than compounds in which carbon forms double or triple bonds. In the following ExpressLab, you will see how each type of bond affects the shape of a molecule. ExpressLab Molecular Shapes The type of bonding affects the shape and 4. Examine the shape of the molecule around movement of a molecule. In this ExpressLab, each carbon atom. Draw diagrams to show your you will build several molecules to examine the observations. shape and character of their bonds. Analysis Procedure 1. Which bond or bonds allow rotation to occur? 1. Build a model for each of the following com- Which bond or bonds are fixed in space? pounds. Use a molecular model kit or a chemical 2.(a) Describe the shape of the molecule around a modelling computer program. carbon atom with only single bonds. CH CH CH CH H C CH CH CH (b) Describe the shape of the molecule around a 3 2 2 3 2 2 3 carbon atom with one double bond and two butane 1–butene single bonds. (c) Describe the shape of the molecule around a H C CH CH CH H C C C CH 2 2 3 3 carbon atom with a triple bond and a single 1,3–butadiene 2–butyne bond. (d) Predict the shape of a molecule around a carbon atom with two double bonds. 2. Identify the different types of bonds in each 3. Molecular model kits are a good representation molecule. of real atomic geometry. Are you able to make a 3. Try to rotate each molecule. Which bonds quadruple bond between two atoms with your allow rotation around the bond? Which bonds model kit? What does this tell you about real prevent rotation? carbon bonding? As you observed in the ExpressLab, the shape of a molecule depends on the type of bond. Table 1.1 describes some shapes that you must know for your study of organic chemistry. In Unit 2, you will learn more about why different shapes and angles form around an atom. 6 MHR • Unit 1 Organic Chemistry Table 1.1 Common Molecular Shapes in Organic Molecules Central atom Shape Diagram carbon with four The shape around this carbon atom is tetrahedral. H single bonds That is, the carbon atom is at the centre of an invisible tetrahedron, with the other four atoms at the vertices of the tetrahedron. This shape results 109.5˚ because the electrons in the four bonds repel each C H other. In the tetrahedral position, the four bonded H atoms and the bonding electrons are as far apart from each other as possible. H carbon with one The shape around this carbon atom is trigonal O H CH double bond and planar. The molecule lies flat in one plane around 3 two single bonds the central carbon atom, with the three bonded 120˚ C C C atoms spread out, as if to touch the corners of a H 120˚ CH H C CH triangle. 3 3 120˚ 3 carbon with two The shape around this carbon atom is linear. The double bonds or two atoms bonded to the carbon atom are stretched 180˚ one triple bond and out to either side to form a straight line. H C C CH3 one single bond oxygen with two A single-bonded oxygen atom forms two bonds. single bonds An oxygen atom also has two pairs of non-bonding lone pairs electrons, called lone pairs. Since there are a total of four electron pairs around a single-bonded oxygen atom, the shape around this oxygen atom O is a variation of the tetrahedral shape. Because H there are only two bonds, however, the shape 104.5˚ around a single-bonded oxygen atom is usually H referred to as bent. Three-Dimensional Structural Diagrams Two-dimensional structural diagrams of organic compounds, such as condensed structural diagrams and line structural diagrams, work well for flat molecules. As shown in the table above, however, molecules containing single-bonded carbon atoms are not flat. You can use a three-dimensional structural diagram to draw the tetra- hedral shape around a single-bonded carbon atom. In a three-dimensional diagram, wedges are used to give the impression that an atom or group is coming forward, out of the page. Dashed or dotted lines are used to show that an atom or group is receding, or being pushed back into the page. In Figure 1.3, the Cl atom is coming forward, and the Br atom is behind. The two H atoms are flat against the surface of the page. The following diagram shows 1-bromoethanol. (You will learn the rules for naming molecules A B such as this later in the chap- ter.) Which atom or group is H coming forward, out of the page? Which atom or group is C receding back, into the page? Br H Cl CH3 C Br H HO Figure 1.3 (A) Three-dimensional structural diagram of the bromochloromethane molecule, BrClCH (B) Ball-and-stick model 2 Chapter 1 Classifying Organic Compounds • MHR 7 Molecular Shape and Polarity The three-dimensional shape of a molecule is particularly important when the molecule contains polar covalent bonds. As you may recall from your previous chemistry course, a polar covalent bond is a covalent bond between two atoms with different electronegativities. Electronegativity is a measure of how strongly an atom attracts electrons in a chemical bond. The electrons in a polar covalent bond are attracted more strongly to the atom with the higher electronegativity. This atom has a partial negative charge, while the other atom has a partial posi- tive charge. Thus, every polar bond has a bond dipole: a partial negative charge and a partial positive charge, separated by the length of the bond. Figure 1.4 illustrates the polarity of a double carbon-oxygen bond. Oxygen has a higher electronegativity than carbon. Therefore, the oxygen atom in a carbon-oxygen bond has a partial negative charge, and the carbon atom has a partial positive charge. partial positive charge partial negative charge δ+ δ− C O dipole vector points from positive charge to negative charge In this unit, you will encounter Figure 1.4 Dipoles are often represented using vectors. Vectors are arrows that have the following polar bonds: direction and location in space. C(cid:3)I, C(cid:3)F, C(cid:3)O, O(cid:3)H, N(cid:3)H, and C(cid:3)N. Use the Other examples of polar covalent bonds include C(cid:3)O, O(cid:3)H, electronegativities in the and N(cid:3)H. Carbon and hydrogen attract electrons to almost the same periodic table to discover degree. Therefore, when carbon is bonded to another carbon atom or which atom in each bond has to a hydrogen atom, the bond is not usually considered to be polar. For a partial negative charge, and example, C(cid:3)C bonds are considered to be non-polar. which has a partial positive charge. Predicting Molecular Polarity A molecule is considered to be polar, or to have a molecular polarity, when the molecule has an overall imbalance of charge. That is, the molecule has a region with a partial positive charge, and a region with a partial negative charge. Surprisingly, not all molecules with polar bonds are polar molecules. For example, a carbon dioxide molecule has two polar C(cid:2)O bonds, but it is not a polar molecule. On the other hand, a water molecule has two polar O(cid:3)H bonds, and it is a polar molecule. How do you predict whether or not a molecule that contains polar bonds has an overall molecular polarity? To determine molecular polarity, you must consider the shape of the molecule and the bond dipoles within the molecule. If equal bond dipoles act in opposite directions in three-dimensional space, they counteract each other. A molecule with identical polar bonds that point in opposite directions is not polar. Figure 1.5 shows two examples, carbon dioxide and carbon tetrachloride. Carbon dioxide, CO , 2 has two polar C(cid:2)O bonds acting in opposite directions, so the molecule is non-polar. Carbon tetrachloride, CCl , has four polar C(cid:3)Cl bonds in 4 a tetrahedral shape. You can prove mathematically that four identical dipoles, pointing toward the vertices of a tetrahedron, counteract each other exactly. (Note that this mathematical proof only applies if all four bonds are identical.) Therefore, carbon tetrachloride is also non-polar. 8 MHR • Unit 1 Organic Chemistry A B Cl •• •• O C O C •• •• Cl Cl Cl Figure 1.5 The red colour indicates a region of negative charge, and the blue colour indicates a region of positive charge. In non-polar molecules, such as carbon dioxide (A) and carbon tetrachloride (B), the charges are distributed evenly around the molecule. If the bond dipoles in a molecule do not counteract each other exactly, the molecule is polar. Two examples are water, H O, and chloroform, CHCl , 2 3 shown in Figure 1.6. Although each molecule has polar bonds, the bond dipoles do not act in exactly opposite directions. The bond dipoles do not counteract each other, so these two molecules are polar. A B H ••O•• C H H Cl Cl Cl Figure 1.6 In polar molecules, such as water (A) and chloroform (B), the charges are distributed unevenly around the molecule. One part of the molecule has an overall negative charge, and another part has an overall positive charge. The steps below summarize how to predict whether or not a molecule is polar. The Sample Problem that follows gives three examples. Note: For the purpose of predicting molecular polarity, you can assume that C(cid:3)H bonds are non-polar. In fact, they have a very low polarity. Step 1 Does the molecule have polar bonds? If your answer is no, see below. If your answer is yes, go to step 2. If a molecule has no polar bonds, it is non-polar. Examples: CH CH CH , CH (cid:2)CH 3 2 3 2 2 Step 2 Is there more than one polar bond? If your answer is no, see below. If your answer is yes, go to step 3. If a molecule contains only one polar bond, it is polar. Examples: CH Cl, CH CH CH Cl 3 3 2 2 Step 3 Do the bond dipoles act in opposite directions and counteract each other? Use your knowledge of three-dimensional molecular shapes to help you answer this question. If in doubt, use a molecular model to help you visualize the shape of the molecule. If a molecule contains bond dipoles that do not counteract each other, the molecule is polar. Examples: H O, CHCl 2 3 If the molecule contains dipoles that counteract each other, the molecule is non-polar. Examples: CO , CCl 2 4 Chapter 1 Classifying Organic Compounds • MHR 9