Introduction to Organic Chemistry: Hydrocarbons

Introduction to Organic Chemistry: Hydrocarbons Chapter 12

Chapter 12 12.1 Organic Compounds 12.2 Alkanes 12.3 Alkanes with Substituents 12.4 Properties of Alkanes 12.5 Alkenes and Alkynes 12.6 Cis-Trans Isomers 12.7 Addition Reactions for Alkenes 12.8 Aromatic Compounds

12.1 Organic Compounds Identify properties characteristic of organic or inorganic compounds.

Organic Compounds Organic chemistry is the study of carbon compounds. An organic compound Always contains carbon and hydrogen atoms May also contain other nonmetals such as oxygen, nitrogen, phosphorus, or a halogen. Organic compounds are found in: Gasoline, medicines, shampoos, plastics, and perfumes Carbohydrates, fats, and proteins

Functional Groups Organic compounds are organized by their functional groups (groups of atoms bonded in a specific way). Compounds that contain the same functional groups have similar physical and chemical properties. The identification of functional groups allows us to classify organic compounds according to their structure, to name compounds within each family, and to predict their chemical reactions.

Organic vs. Inorganic In chemistry, molecules are classified as Organic or Inorganic. Inorganic compounds are (quite expansively) anything that is not organic. Organic and Inorganic compounds have different properties. Organic compounds: Have low melting and boiling points. Are flammable and undergo combustion. Are not soluble in water. Inorganic compounds Many inorganic compounds have high melting and boiling points. Inorganic compounds that are ionic are usually soluble in water, and most do not burn in air.

Practice Identify each characteristic as most typical of compounds that are inorganic or organic. A. It has a high melting point. B. It is not soluble in water. C. It contains carbon and hydrogen atoms. D. It has the formula MgCl 2. E. It burns easily in air.

Representations of Carbon Compounds Hydrocarbons are organic compounds that consist of only carbon and hydrogen. In organic molecules, every carbon atom has four bonds. In methane (CH4), the carbon atom forms an octet by sharing its four valence electrons with four hydrogen atoms. Three-dimensional and two-dimensional representations of methane: a) space-filling model, b) ball-and-stick model, c) wedge-dash model, d) expanded structural formula, and e) condensed structural formula

Representations of Carbon Compounds In ethane (C 2 H 6 ), each tetrahedral carbon forms three covalent bonds to hydrogen and one to the other carbon.

Alkanes Alkanes are formed by a continuous chain of carbon atoms. are named using the IUPAC (International Union of Pure and Applied Chemistry) system. have names that end in ane. use Greek prefixes to name carbon chains with five or more carbon atoms.

Study Check In the butane molecule (C 4 H 10 ), predict the shape around each carbon atom. H H H H H C C C C H H H H H

12.2 - Alkanes Write the IUPAC names and draw the condensed or line-angle structural formulas for alkanes and cycloalkanes.

Alkanes More than 90% of the compounds in the world are organic compounds. The larger number of carbon compounds is possible because the covalent bonds between carbon atoms (C-C) is very strong, allowing carbon atoms to form long, stable chains.

Alkanes The alkanes are a type of hydrocarbon in which the carbon atoms are connected only by single bonds. Alkanes are formed by a continuous chain of carbon atoms. The names of alkanes and in ane. Such names are part of the IUPAC system (International Union of Pure and Applied Chemistry) used by chemists to name organic chemistry. Alkanes made of carbon chains are named based on how many carbons make up the chain. One of the most common uses of alkanes is as fuels. Methane, propane, octane, and hexane are all alkanes used as fuels.

IUPAC Names of Alkanes

Line-Angle Structural Formulas A simplified structure of organic molecules is called the line-angle structural formula. shows a zigzag line in which carbon atoms are represented as the ends of each line and as corners. Carbon atoms at the end are bonded to three hydrogen atoms. in the middle are bonded to two hydrogen atoms.

Condensed formula and Line-angle formula Pentane

Condensed formula and Line-angle formula Draw the condensed structural formula and name the molecule:

Guide to Drawing Structural Formulas for Alkanes Step 1: Draw the carbon chain. Step 2: Draw the expanded structural formula by adding the hydrogen atoms using single bonds to each of the carbon atoms. Step 3: Draw the condensed structural formula by combining the H atoms with each C atom. Step 4: Draw the line-angle structural formula as a zigzag line in which the ends and corners represent C atoms.

Drawing Expanded, Condensed, and Line- Angle Structural Formulas (1 of 3) Draw the expanded, condensed, and line-angle structural formula for pentane. Step 1: Draw the carbon chain. A molecule of pentane has five carbon atoms in a continuous chain. Step 2: Draw the expanded structural formula by adding the hydrogen atoms, using single bonds to each of the carbon atoms.

Drawing Expanded, Condensed, and Line- Angle Structural Formulas (2 of 3) Draw the expanded, condensed, and line-angle structural formula for pentane. Step 3: Draw the condensed structural formula by combining the H atoms with each C atom.

Drawing Expanded, Condensed, and Line- Angle Structural Formulas (3 of 3) Draw the expanded, condensed, and line-angle structural formula for pentane. Step 4: Draw the line-angle structural formula as a zigzag line in which the ends and corners represent C atoms.

Conformations of Alkanes Single bonds can spin and rotate. Thus different arrangements, known as conformations, occur during the rotation about a single bond. http://symmetry.otterbein.edu/gallery/index.html

Structural Formulas: C 4 H 10 As butane (C 4 H 10 ) rotates, sometimes the line up in front of each other, and at other times they are opposite each other. Butane can be drawn using a variety of two-dimensional condensed structural formulas:

Structural Formulas: C 4 H 10

Cycloalkanes Hydrocarbons can also form into circles or rings called: cycloalkanes have two fewer hydrogen atoms than the open chain form. are named by using the prefix cyclo before the name of the alkane chain with the same number of carbon atoms.

Formulas of Cycloalkanes Table 12.4 Formulas of Some Common Cycloalkanes Name BLANK BLANK BLANK Cyclopropane Cyclobutane Cyclopentane Cyclohexane Ball-and-Stick Model BLANK BLANK BLANK Three carbons single-bonded to each other in a triangular pattern, with each carbon single-bonded to 2 hydrogens. The ball and stick model shows four carbons single-bonded to each other in a square pattern, with each carbon singlebonded to 2 hydrogens. The ball and stick model shows five carbons single-bonded to each other in a pentagonal pattern, with each carbon single-bonded to 2 hydrogens. The ball and stick model shows six carbons single-bonded to each other in a hexagonal pattern, with each carbon single-bonded to 2 hydrogens. Condensed Structural Formula BLANK BLANK BLANK The condensed structural formula shows a triangular ring of three C H 2 molecules. The condensed structural formula shows a square ring of four C H 2 molecules. The condensed structural formula shows a pentagonal ring of five C H 2 molecules. The condensed structural formula shows a hexagonal ring of six C H 2 molecules. Line-Angle Structural Formula BLANK BLANK BLANK The line-angle structural formula is a triangle. The line-angle structural formula shows a square. The line-angle structural formula shows a pentagon. The line-angle structural formula shows a hexagon.

Study Check Give the IUPAC name for each of the following compounds: A. B.

Study Check Name the following alkanes: A. B. C. D.

12.3 Alkanes and Substituents Write the IUPAC names for alkanes with substituents and draw their condensed and line-angle structural formulas.

Structural Isomers Structural isomers have the same molecular formula with a different arrangement of atoms. have the same number of atoms bonded in a different order. Butane (C 4 H 10 ) has two structural isomers: a straight chain and a branched chain.

Study Check Draw three possible structural isomers of pentane (C 5 H 12 ).

Solution Draw three possible structural isomers of pentane (C 5 H 12 ). Structural Isomers of C 5 H 12 Structural Isomers of C 5 H 12 Structural Isomers of C 5 H 12 Structural Isomers of C 5 H 12 Condensed The first condensed structural formula is a straight chain of single-bonded molecules as follows. C H 3, C H 2, C H 2, C H 2, C H 3. The second condensed structural formula is a branched chain as follows. C H 3, C H single-bonded to C H 3 above, C H 2, C H 3. The third condensed structural formula is a central C single-bonded to four C H 3 molecules above, below, rightward, and leftward. Line-Angle The line-angle structural formula shows a zigzag line made of 4 segments forming 3 angles. The line-angle structural formula shows a zigzag of 3 segments forming 2 angles, with a fourth segment rising vertically from the first angle. The line-angle structural formula shows 2 rising and falling line segments with 2 segments rising diagonally right and left from the angle.

Study Check Is the pair of formulas structural isomers? Or the same molecule?

Substituents in Alkanes When CH 3 branches off of a carbon chain, it s called an alkyl group When a halogen atom (Group 17) is attached to a carbon chain, it is named as a halo group with the terms fluoro, -chloro, -bromo, -iodo based on which element it is.

Substituents and Alkyl Groups Table 12.5 Formulas and Names of Some Common Substituents Formula Name Formula, C H 3, single bond. name, methyl. Formula, straight chain, C H 3, C H 2, single bond. name, ethyl. BLANK BLANK Formula Name Formula, straight chain, C H 3, C H 2, C H 2, single bond. name, propyl. Formula, branched chain, C H 3, C H with single bond above, C H 3. name, isopropyl. BLANK BLANK Formula Name Formula, straight chain, C H 3, C H 2, C H 2, C H 2, single bond. name, butyl. Formula, branched chain, C H 3, C H single-bonded to C H 3 above, C H 2, single bond. name, isobutyl. Formula, C H 3, C H with single bond above, C H 2, C H 3. name, secondary butyl. Formula, central C with single bond above and three C H 3 molecules below, rightward, and leftward. name, tertiary butyl. Formula Name Formula, F, single bond. name, fluoro. Formula, F, single bond. name, fluoro. Formula, B r, single bond. name, bromo. Formula, I, single bond. name, iodo.

Naming Alkanes with Substituents

Naming Cycloalkanes with Substituents

Naming Haloalkanes Haloalkanes are alakanes with a halogen atom that replaces a hydrogen atom. are named by putting the substituents in alphabetical order. have the halo group numbered according to the carbon where it is attached to the alkane. Examples of Haloalkanes Formula BLANK BLANK BLANK BLANK straight chain, C H 3, C l straight chain, C H 3, C H 2, B r Branched chain, C H 3, C H single-bonded to an F above A central C single-bonded to C l above and three C H 3 molecules below, rightward, and leftward IUPAC Chloromethane Bromoethane 2-Fluoropropane 2-Chloro-2- methylpropane Common Methyl chloride Ethyl bromide Isopropyl fluoride Tert-Butyl chloride

Drawing the molecule from the name Draw the condensed and line-angle structural formulas for 2,3-dimethylbutane.

Drawing the molecule from the name Draw the condensed and line-angle structural formulas for 2-bromo-3-ethyl-4-methylpentane.

12.4 Properties of Alkanes Identify the properties of alkanes and write a balanced chemical equation for combustion.

Properties of Alkanes Many types of alkanes are the components of fuels that power our cars and oil that heats our home. The solid alkanes that make up waxy coatings on fruits and vegetables help retain moisture, inhibit mold, and enhance appearance. The different uses of alkane compounds result from their physical properties, including their solubility and density.

Uses of Alkanes (1 of 2) Alkanes with one to four carbons are gases at room temperature and are widely used as heating fuels. methane, ethane, propane, butane Butane has four carbons: Alkanes with five to eight carbons are highly volatile liquids at room temperature, which makes them useful as fuels. pentane, hexane, heptane, octane Octane has eight carbons:

Uses of Alkanes (2 of 2) Alkanes with 9 17 carbons are liquids with higher boiling points and are found in motor oils, mineral oil, kerosene, diesel, and jet fuels. Decane has 10 carbons: Alkanes with 18 or more carbon atoms, known as paraffins, are waxy solids at room temperature. Petroleum jelly, or Vaseline, is a semisolid mixture of hydrocarbons with more than 25 carbon atoms.

Melting and Boiling Points (1 of 4) Alkanes have the lowest melting and boiling points of organic compounds. contain only the nonpolar bonds of exhibit only weak dispersion forces in the solid and liquid states. Longer-chain alkanes have more dispersion forces.

Melting and Boiling Points (2 of 4) Branched alkanes have lower boiling points than the straight-chain isomers.

Melting and Boiling Points (2 of 4) Branched alkanes have lower boiling points than the straight-chain isomers. tend to be more compact, reducing the points of contact between the molecules. do not have linear shapes and cannot line up close to each other.

Melting and Boiling Points (3 of 4) Cycloalkanes have higher boiling points than the straight-chain alkanes with the same number of carbon atoms. have limited rotation of carbon bonds; they maintain their rigid structure and can be stacked closely together, which gives them many points of contact and attractions to each other.

Straight chain alkanes. condensed structural formula, C H 3, C H 2, C H 2, C H 2, C H 3 Branched chain alkanes. condensed structural formula, C H 3, C H single-bonded to C H 3, C H 2, C H 3 Central C single-bonded to four C H 3 molecules line-angle structural formula, a pentagonal ring Melting and Boiling Points (4 of 4) We can compare the boiling points of straight-chain alkanes, branched-chain alkanes, and cycloalkanes. Table 12.6 Comparison of Boiling Points of Alkanes and Cycloalkanes with Five Carbons Formula Name Boiling Point ( C) Straight-Chain Alkane BLANK BLANK Pentane 36 Branched-Chain Alkanes BLANK BLANK 2-Methylbutane 28 Dimethylpropane 10 Cycloalkane BLANK BLANK Cyclopentane 49

Combustion of Alkanes (1 of 3) The carbon carbon single bonds in alkanes are difficult to break, which makes them the least reactive family of organic compounds. However, alkanes burn readily in oxygen to produce carbon dioxide, water, and energy. g g g g Alkane O2 CO2 H2O + energy

Combustion of Alkanes (3 of 3) Methane is the natural gas we use to cook our food and heat our homes. The equation for the combustion of methane (CH 4 ) is written as follows: g g g g CH 2O CO 2H O + energy 4 2 2 2 Propane is the gas used in portable heaters and gas barbecues. The equation for the combustion of propane (C 3 H 8 ) is written as follows: g g g g CH 5O 3CO 4H O + energy 4 2 2 2

Solubility and Density of Alkanes Alkanes are nonpolar. insoluble in water. less dense than water. flammable in air. found in crude oil. If there is an oil spill in the ocean, the alkanes in the crude oil do not mix with the water but float on top, forming a thin layer on the surface.

12.5 Alkenes and Alkynes Identify structural formulas as alkenes, cycloalkenes, and alkynes and write their IUPAC names.

Alkenes and Alkynes Alkenes are hydrocarbons that contain double bonds. Alkynes are hydrocarbons that contain triple bonds are called unsaturated hydrocarbons because they do not contain the maximum number of hydrogen atoms. react with hydrogen gas to increase the number of hydrogen atoms and become alkanes. Remember, carbon atoms always form four covalent bonds.

Identifying Alkenes Alkenes contain one or more carbon carbon double bonds. In ethene (C 2 H 4 ), two carbon atoms are connected by a double bond. Each carbon atom in the double bond is attached to two hydrogen atoms and has a trigonal planar arrangement with bond angles of 120.

Ethene (C 2 H 4 ) Ethene (C 2 H 4 ), more commonly called ethylene, is an important plant hormone involved in promoting the ripening of fruits such as bananas. accelerates the breakdown of cellulose in plants, which causes flowers to wilt and leaves to fall from trees.

Other alkene examples

Identifying Alkynes Alkynes contain one or more carbon carbon triple bonds. In ethyne (C 2 H 2 ), each carbon is also bonded to one H atom. Each carbon atom in the triple bond has a linear arrangement with bond angles of 180.

Ethyne (C 2 H 2 ) Ethyne (C 2 H 2 ), more commonly called acetylene Is used in welding where it reacts with oxygen to produce flames with temperatures above 3300 C

Other alkyne examples

Study Check (1 of 4) Identify each of the following compounds as an alkene or alkyne: A. B.

Naming Alkanes, Alkenes, and Alkynes The IUPAC names for alkenes and alkynes are similar to those of alkanes. use the alkane name with the same number of carbon atoms, replacing the ane ending with ene. Cyclic alkenes are named as cycloalkenes. Table 12.7 Comparison of Names for Alkanes, Alkenes, and Alkynes

Study Check Write IUPAC name for the following:

Solution (1 of 4) Step 1: Name the longest carbon chain that contains the double or triple bond. Analyze the Problem Given five-carbon chain double bond, methyl group Need IUPAC name five carbon atoms pentene Analyze the Problem Given six-carbon triple bond Need IUPAC name six carbon atoms hexyne A. B.

Solution (2 of 4) Step 2: Number the carbon chain, starting from the end nearer the double or triple bond. A. 1 2 3 4 5 2-pentene B. 6 5 4 3 2 1 2-hexyne

Solution (3 of 4) Step 3: Give the location and name of each substituent (alphabetical order) as a prefix to the alkeneor alkyne name. A. 1 2 3 4 5 4-methyl-2-pentene B. 6 5 4 3 2 1 2-hexyne; there are no substituents in this compound.

Naming Cycloalkenes Cycloalkenes have a double bond within a ring structure and are named by assigning the double bond to be between carbon 1 and carbon 2 when a substituent is on the ring. do not need to include the numbers for the double bond. 3-methylcyclopentene (It is understood that the double bond is between carbon 1 and carbon 2.) The carbon atoms in the ring are numbered to give the double bond numbers 1 and 2 and the lowest possible number to any substituents present.

Study Check (4 of 4) Name the following alkenes and alkynes:

Solution (4 of 4) Name the following alkenes and alkynes: cyclohexene 3,3-dimethylcyclopentene

Chemistry Link to the Environment: Fragrant Alkenes (1 of 2) The odors you associate with lemons, oranges, roses, and lavender come from the volatile compounds that are synthesized by the plants that produce these flowers and fruits. Often these compounds contain double or triple bonds or ring structures; they are unsaturated.

Cis Trans Isomers In an alkene, the double bond is rigid and does not rotate.

Cis Trans Isomers (1 of 2) In an alkene, the double bond is rigid and does not rotate. holds attached groups in fixed positions. makes cis trans isomers (geometric isomers) possible when two different groups are attached to the carbon atoms on each side of the double bond. requires a prefix of cis or trans to reflect the arrangement of groups across the double bond.

Cis Trans Isomers Cis trans isomers have different physical and chemical properties.

Cis Trans Isomers of Butene In a cis isomer, the alkyl groups are attached on the same side of the double bond and H atoms are on the other side. In the trans isomer, the groups and H atoms are attached on opposite sides of the double bond.

Cis Trans Isomers (2 of 2) Cis trans isomers cannot occur when two groups are the same on one of the carbons.

Chemistry Link to the Environment: Pheromones (1 of 2) Many insects emit minute quantities of chemicals called pheromones to send others of the same species messages. Pheromones may warn an insect of danger. mark a trail. attract the opposite sex.

Chemistry Link to the Environment: Pheromones (2 of 2) The effectiveness of many of these pheromones depends on the cis or trans configuration of the double bonds in the molecules. One pheromone is bombykol, the sex pheromone produced by the female silkworm moth. which contains one cis double bond and one trans double bond.

Cis Trans Isomers Identify each of the following as cis or trans

Naming Cis Trans Isomers The prefix of cis or trans is placed in front of the alkene name when the compound is a cis or trans isomer.

Study Check Name, using cis or trans prefixes when needed.

Solution Name each, using cis or trans prefixes when needed. A. cis-2,3-dichlorobutene B. trans-2,3-dibromobutene C. trans-2-butene

12.7 Addition Reactions for Alkenes Draw the condensed or line-angle structural formulas and give the names of the organic products of addition reactions of alkenes. Draw a condensed structural formula for a section of a polymer.

Addition Reactions Alkanes are very stable and nonreactive. Alkenes and Alkynes, on the other hand, react readily with other molecules due to the double and triple bonds. These bonds act as an electron source. (Two electrons per bond.) Addition reactions are the most common, where something is added to each carbon in the double or triple bond. We will focus on alkenes, however these reactions can apply to alkynes as well.

Hydrogenation In hydrogenation, H atoms add to each of the carbon atoms in a double bond of an alkene. During hydrogenation, the double bonds are converted to single bonds of alkanes. A catalyst, such as platinum (Pt), nickel (Ni), or palladium (Pd) is used to speed up the reaction.

Practice

Hydration In hydration, an alkene reactions with water (H-OH). A hydrogen atom (H-) from water forms a bond with one carbon atom in the double bond, and the oxygen atom in (-OH) forms a bond with the other carbon. The reaction is catalyzed by a strong acid, such as H 2 SO 4, written as H +. Hydration is used to prepare alcohols, which have the hydroxyl (-OH) functional group.

Hydration Markovnikov s Rule When water is added to an asymmetrical alkene, the H is added to the carbon with more H s already attached. The OH bonds to the other carbon.

Practice

Polymerization A polymer is a large molecule that consists of small repeating units called monomers. Many of these polymers are produced by addition reactions of alkenes. In the past hundred years, the plastics industry has made synthetic polymers such as those in carpeting, plastic wrap, nonstick pans, artificial joins, heart valves, and rain gear.

Polymerization Polymerization is the addition, or connecting, of two alkenes, end-to-end. These reactions require: high temperature a catalyst higher pressure (over 1000 atm) In an addition reaction, a polymer grows longer as each monomer is added at the end of the chain.

Practice Draw a portion of a polymer made from polydichloroethene.

12.8 Aromatic Compounds Describe the bonding in benzene; name aromatic compounds, and draw their line-angle structural formulas.

Benzene In 1825, Michael Faraday isolated a hydrocarbon called benzene. Benzene is: An aromatic compound A ring of six C atoms, each bonded to one H atom A flat ring structure draw with three alternating double bonds. Represented by two structures, because the electrons are shared equally among all the C atoms Represented by a line-angle structural formula using a cirl in the center instead of alternating double bonds.

Aromatic Compounds An aromatic compound is a compound with at least one benzene ring in it. This class was called aromatic because when they were initially discovered, it was found they often were the source of smells.

Naming Aromatic Compounds (1 of 5) Aromatic compounds containing a benzene ring and a single substituent are named as benzene derivatives. Since the ring contains only one substituent, the ring is not numbered. Some common names such as toluene, aniline, and phenol are allowed by IUPAC rules.

Naming Aromatic Compounds (2 of 5) When a benzene ring is a substituent, C 6 H 5, it is named as a phenyl group.

Naming Aromatic Compounds (3 of 5) When there are two or more substituents, the benzene ring is numbered to give the lowest numbers to the substituents ortho, meta, para

Naming Aromatic Compounds (4 of 5) When a common name such as toluene, phenol, or aniline can be used, the carbon atom attached to the methyl, hydroxyl, or amine group is numbered as carbon 1. prefixes are used to show the position of the two substituents.

Naming Aromatic Compounds (5 of 5) The common name xylene is used for the isomers of dimethylbenzene. If three or more substituents are attached to the benzene ring, they are numbered in the direction to give the lowest set of numbers and then named alphabetically.

Study Check (1 of 2) Select the correct name for each compound. 1. 2. A. chlorocyclohexane B. chlorobenzene C. 1-chlorobenzene A. 1,2-dimethylbenzene B. 1,4-dimethylbenzene C. 1,3-dimethylbenzene