Chapter 11 Introduction to Organic Chemistry: Alkanes General, Organic, and Biological Chemistry Fourth Edition Karen Timberlake Chapter 11 Introduction to Organic Chemistry: Alkanes 11.1 Organic Compounds Lectures © 2013 Pearson Education, Inc.

Organic Compounds An organic compound typically contains carbon and hydrogen atoms, and may also contain other atoms, such as, O, S, N, P, or a halogen (F, Cl, Br and I). Propane, C3H8

Properties of Organic Compounds Many organic compounds are nonpolar and have weak attractions between molecules. have low melting and boiling points. are not soluble in water. are less dense than water. are highly flammable. Oil (organic) and water (inorganic)

Properties of Organic and Inorganic Compounds Typical properties of organic compounds, such as propane, C3H8, and inorganic compounds, such as sodium chloride, NaCl.

Organic Compounds, Bonding Hydrocarbons are organic compounds that consist of carbon and hydrogen atoms. have electron-dot formulas that have four bonds on each carbon atom. Hydrocarbons with only single bonds are called saturated hydrocarbons. Methane, CH4 is the simplest hydrocarbon.

Tetrahedral Structure of Carbon VSEPR theory predicts that a carbon atom with four single covalent bonds is tetrahedral as shown in a A. tetrahedron. B. ball-and-stick model. C. space-filling model. D. expanded structural formula.

Tetrahedral shape of Ethane, C2H6 In ethane, each carbon atom is bonded to another carbon atom and three hydrogen atoms. each carbon atom has a tetrahedral shape. Representations of ethane, C2H6: (a) tetrahedral shape of each carbon, (b) ball-and-stick model, (c) space-filling model, (d) expanded structural formula.

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.

IUPAC Names for Alkanes Insert table 11.2 pg 415 The names of organic compounds are determined by the IUPAC rules (International Union of Pure and Applied Chemistry). The stem of the name states the number of carbon atoms in the carbon chain of the compounds. The suffix, in this case –ane, indicates the alkane family.

Structural Formulas Alkanes are written with structural formulas that are expanded to show each bond. condensed to show each carbon atom and the attached hydrogen atoms. In methane, CH4 the four valence electrons of carbon are shared with the single electrons of four hydrogen (H) atoms. Each pair of electrons is a single bond, which can be drawn as a line. When a structure is drawn to show each bond, it is called a complete structural formula.

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 or skeletal formula abbreviates the carbon atoms and shows only the zigzag pattern of bonds between carbon atoms. Heptane has 7 carbon atoms.

Types of Structural Formulas

Rotation Around a C C Single Bond The groups attached to a C—C single bond rotate around the bond freely to give different relative structural arrangements called conformations. sometimes the –CH3 groups line up, sometimes they are opposite each other.

Butane, C4H10 Structural Representations Butane can be drawn using a variety of two-dimensional, condensed structural formulas. Rotation of the end CH3-groups provides different structural arrangements for butane.

Drawing Structural Formulas A molecule of pentane, C5H12 has five carbon atoms connected to each other and to hydrogen atoms with single bonds to give each carbon four bonds. In a condensed structural formula, carbon atoms on each end are written as CH3—. in the middle are written as —CH2—. The skeletal formula is a zigzag line where the ends and corners represent carbon atoms.

Drawing Structural Formulas

Cycloalkanes Cycloalkanes are carbon rings. have two fewer hydrogen atoms than straight-chain alkanes with the same number of carbon atoms. are named by using the prefix cyclo- before the name of the alkane chain.

Structures of Cycloalkanes Cycloalkanes are often represented by skeletal formulas, which appear as a simple geometric figure.

Substituents Alkanes with four or more carbons can have side groups called branches or substituents, which are attached to the carbon chain. that replace at least one H on the alkane chain. When two compounds have the same molecular formula, but differ in the order in which the atoms are bonded, they are called structural isomers.

Structural Isomers of C4H10 have the same molecular formula. have different structural arrangements. of C4H10 consist of a straight chain and a branched chain, each with 4 carbon atoms. branch or substituent 20

Isomers of Pentane (C5H12) have the same molecular formula. have different structural arrangements. consist of a straight chain and two branched chains. 21

Isomers of Alkanes The number of structural isomers of alkanes increases rapidly as the number of carbon atoms increases. Insert table of structural isomers middle pg 420 22

Alkyl Groups Alkyl groups are carbon branches. are named by replacing the -ane ending of the corresponding alkane name with yl. methane = methyl —CH3 ethane = ethyl —CH2—CH3 propane = propyl —CH2—CH2—CH3 23

Halo Groups Halo groups are halogen atoms attached to the carbon chain. are named fluoro (—F), chloro (—Cl), bromo (—Br) or iodo (—I). 24

Common Substituents 25

Naming Alkanes with Substituents 26

Naming Alkanes with Substituents Name the following alkane. Step 1 Write the alkane name of the longest chain of carbon atoms. 5 C pentane Step 2 Number the carbon atoms starting from the end nearer a substituent. 27

Naming Alkanes with Substituents Name the following alkane. Step 3 Give the location and name of each substituent (alphabetical order) as a prefix to the name of the main chain. 2-methylpentane 28

Naming Alkanes with Alkyl Groups methylpropane 2,4-dimethylpentane 29

Naming Haloalkanes In a haloalkane, halogen atoms replace hydrogen atoms. substituents are numbered and arranged alphabetically. alkanes with halogens can be named as alkyl halides; the carbon group is named as an alkyl group followed by the halide name. CH3—CH2—Cl CH3—Br IUPAC Name chloroethane bromomethane Common Name ethyl chloride methyl bromide 30

Naming Cycloalkanes with Substituents When naming a cycloalkane with a substituent the name of the substituent is placed in front of the cycloalkane name. the number of the substituent is not needed when there is only one substituent. If two or more substituent’s are attached, the ring is numbered by assigning carbon 1 to the substituent that comes first alphabetically. 31

Naming Cycloalkanes with Substituents The name of a substituent is placed in front of the cycloalkane name. Methylcyclobutane When there are two substituents, number the ring 1-bromo-2-chlorocyclopentane. 32

Guide to Drawing Alkane Structures 33

What Is in a Name? The structural formula is drawn from the IUPAC name. 2,4-dimethylhexane 2,4 dimethyl hexane Location of Two CH3- groups 6-carbon main chain branches on attached with single C—C carbon main chain atoms 34

Alkanes: Physical States Alkanes are gases when they have only 1 to 4 carbon atoms. liquids when they have 5 to 8 carbon atoms. solids when they have 9 to 17 carbon atoms.

Alkanes: Solubility and Density Alkanes are nonpolar. insoluble in water. less dense than water (1.0 g/mL) with a density from (0.62 g/mL to 0.79 g/mL). Vegetable oil, an organic compound, is not soluble in water.

Alkanes in Oil If there is an oil spill, alkanes in the oil do not mix with the water, alkanes form a thin layer on the surface of the water spreading large distances, cleanup includes mechanical, chemical, and microbiological methods, In oil spills, large quantities of oil spread over the surface of the water.

Alkanes: Melting and Boiling Points have the lowest melting and boiling points of all organic compounds. have only nonpolar bonds, C—C and C—H. have weak dispersion forces which increase when more carbons are present.

Branched Alkanes: Melting and Boiling Points The boiling and melting points of branched alkanes are lower than their straight-chain isomers because they are more compact. There is more contact between hexane molecules (red and black licorice) than between the surfaces of 2,3-dimethylbutane molecules (tennis balls).

Cycloalkanes: Melting and Boiling Points Cycloalkanes have higher boiling points than straight-chain alkanes with the same number of carbon atoms. restricted rotation around C—C bonds, maintaining rigid structures.

Combustion of Alkanes Alkanes contain single C—C bonds which are difficult to break. are the least reactive group of organic compounds. burn readily in the presence of oxygen. undergo combustion to produce carbon dioxide, water, and energy.

Combustion of Alkanes We use methane gas to cook food and heat homes. Propane gas is used in portable heaters and gas barbecues. Our cells get energy from the combustion of glucose.

Balancing a Combustion Equation Write the equation: Balance C: Balance H: Balance O with O2:

Crude Oil Hydrocarbons in crude oil are separated by their different boiling points in a process called fractional distillation which removes groups of hydrocarbons by continually heating the mixture to higher temperatures.

Crude Oil

Elements in Organic Compounds In organic molecules, carbon atoms can form bonds with atoms of O, S, N, P, or halogens, F, Cl, and Br. 46

Functional Groups Functional groups are a characteristic feature of organic molecules that behave in a predictable way. are composed of an atom or a group of atoms. are groups that replace a H in the corresponding alkane. provide a way to classify families of organic compounds. 47

Some Functional Groups 48

Alkenes and Alkynes Alkenes contain a double bond between adjacent carbon atoms. Alkynes contain a triple bond. Aromatic compounds contain a benzene ring. 49

Alcohols, Thiols, and Ethers An alcohol contains the hydroxyl (–OH) functional group. Thiols contain a thiol (–SH) functional group. In an ether, an oxygen atom is bonded to two carbon atoms (–C–O–C–). Thiol 50

Aldehydes and Ketones An aldehyde contains a carbonyl group (C=O), which is a carbon atom with a double bond to an oxygen atom, attached to at least one hydrogen atom. In a ketone, the carbon of the carbonyl group is attached to two other carbon atoms. 51

Carboxylic Acids and Esters Carboxylic acids contain the carboxyl group, which is a carbonyl group attached to a hydroxyl group. An ester contains the carboxyl group between carbon atoms. 52

Amines and Amides In an amine, the functional group is a nitrogen atom. In an amide, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group. 53