Chemeketa Community College Chapter 10: Organic Chemistry Larry Emme Chemeketa Community College

Chapter Outline Alkanes Modifiers cycloalkanes Properties of alkanes Functional Groups

Organic Chemistry 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.

Organic Compounds Typical organic compounds 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)

Organic vs. Inorganic Propane, C3H8, is an organic compound used as a fuel. NaCl, salt, is an inorganic compound composed of Na+ and Cl− ions. Why is propane organic, but NaCl is not?

Comparing Organic and Inorganic Compounds

Writing Formulas for Alkanes Only single bonds! Saturated In organic compounds, carbon has 4 valence electrons and hydrogen has 1. • • C • H • carbon achieves an octet by forming four bonds. H H   H  C  H H C H H H CH4, methane First member of the Alkanes

Paraffin is the common name of the alkane family.

Organic Chemistry’s Golden Rule: Carbon always forms 4 bonds. 9

Tetrahedral Structure of Carbon VSEPR theory predicts that a carbon atom with four single, covalent bonds has a tetrahedral shape.

Organic Molecules In organic molecules, valence electrons are shared. covalent bonds form between carbon atoms. H H H H • • • • H  C  C  H H C C H H H H H Ethane, CH3─CH3 Second member of the Alkanes

Tetrahedral Structure of Carbon In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape.

Structural Formulas Alkanes are written with structural formulas that are Expanded (Structural) to show each bond. condensed to show each carbon atom and its attached hydrogen atoms. Expanded Condensed H H C H CH4 , methane 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.

Expanded and Condensed Structures 1st Member 2nd Member 3rd Member

Structural Formulas Condensed formulas are written for expanded structural formula by showing each carbon and the attached hydrogen atoms. Expanded Condensed H H H H │ │ │ │ H─C ─C ─C ─ C ─ H CH3─CH2─CH2─CH3

Types of formulas and models used to represent organic molecules Types of formulas and models used to represent organic molecules. Each diagram is a representation of a propane molecule. or CH3−CH2−CH3 16 16

Modified Skeleton formula Structural formula Skeleton formula Modified Skeleton formula Remove H’s Remove H bonds Remove C’s Line structure 17

This is an example of how to change a condensed formula into a line structure. 18 18

Write the molecular formula for the following hydrocarbon:

C12H24 Write the molecular formula for the following hydrocarbon: H H

Names of Alkanes – saturated hydrocarbons The names of alkanes (Paraffins – only single bonds) are determined by the IUPAC (International Union of Pure and Applied Chemistry) system. end in –ane. with 1-4 carbons in a chain use prefixes as follows: Name # Carbons Condensed Structural ______Formula_______ Methane 1 CH4 Ethane 2 CH3―CH3 Propane 3 CH3―CH2―CH3 Butane 4 CH3―CH2―CH2―CH3

Names of Alkanes Alkanes with 5-10 carbon atoms in a chain use Greek prefixes. Name # Carbons Structural Formula Pentane 5 CH3CH2CH2CH2CH3 Hexane 6 CH3CH2CH2CH2CH2CH3 Heptane 7 CH3CH2CH2CH2CH2CH2CH3 Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3 Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3 Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 CH3(CH2)8CH3

Writing Structural Formulas Carbon atoms in a chain maintain tetrahedral shape. are connected in a zigzag pattern. are drawn as 2-dimensional. can be written in several conformations.

Some Structures for Butane normal- or n- Copyright © 2009 by Pearson Education, Inc.

Hexane Has Six Carbon Atoms is an alkane with six carbon atoms in a continuous chain. has a “zigzag” look because each carbon atom is at the center of a tetrahedron. is represented by a ball-and-stick model as shown below.

Cycloalkanes Cycloalkanes are cyclic alkanes. have two hydrogen atoms 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.

Cycloalkanes The structural formulas of cycloalkanes are usually represented by geometric figures.

More Cycloalkanes

Learning Check Name the following. A. CH3─CH2─CH2─CH3 B. C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3 D.

Learning Check Answers Name the following. A. CH3─CH2─CH2─CH3 B. C. CH3─CH2─CH2─CH2─CH2─CH2─CH2─CH3 D. normal-butane or n-butane cyclopropane normal-octane or n-octane cyclohexane

Alkanes with Modifiers (Substituents) Anything other than a hydrogen!

Isomers of Butane Isomers have the same molecular formula. normal-butane Isomers have the same molecular formula. have different atom arrangements. of butane (C4H10) are a straight chain and a branched chain. branch iso-butane

Isomers are compounds that have the same molecular formula, but different structural formulas.

The old way to name hydrocarbons was based on the total number of carbons in the molecule, e.g., normal- & iso- butanes. However, as the number of carbons increases, the number of possible isomers with the same formula increases even faster. We need a better approach. The IUPAC union decided to name hydrocarbons based on the longest continuous carbon chain and not on the total number of carbon atoms. Carbon atoms off the main chain are called branches or alkyl groups and require a slight change in the way they are named.

Alkyl groups (branches off the main carbon chain) Alkyl groups are alkanes that are missing one H. substituents attached to carbon chains. named with a –yl ending. CH3 methyl CH3 CH2 ethyl

Naming Modifiers (Substituents ) Names and Formulas of Some Common Modifiers In the IUPAC system, a carbon branch is named as an alkyl group. halogen atoms are named as halo. Modifier Name

Guide to Naming Alkanes Write the alkane name of the longest chain of carbon atoms 1 Number the carbon atoms starting from the end nearest a modifier 2 Give the location and name of each modifier (alphabetical order) as a prefix to the name of the main chain 3

Alkanes with Modifiers (Substituents) CH3 CH3 CH CH3 methylpropane methyl groups CH3 CH3 CH3 CH CH2 CH CH3 2,4-dimethylpentane

Naming Alkanes Give the name of CH3 CH3   CH3─CH─CH─CH3   CH3─CH─CH─CH3 STEP 1: Name the longest continuous chain. CH3 CH3 butane

Naming Alkanes Give the name of CH3 CH3   CH3─CH─CH─CH3   CH3─CH─CH─CH3 STEP 2: Number chain. CH3 CH3 1 2 3 4 STEP 3: Locate substituents and name. 2,3-dimethylbutane

Learning Check Give the IUPAC name for each of the following: A. CH3 CH3 | | CH3─CH─CH2 ─CH─CH3 B. Cl CH3 CH3─CH2─CH─CH2─C─CH2─CH3 | Cl

Learning Check Answers Give the IUPAC name for each of the following: A. CH3 CH3 | | CH3─CH─CH2 ─CH─CH3 B. Cl CH3 CH3─CH2─CH─CH2─C─CH2─CH3 | Cl 2,4-dimethylpentane 1 2 3 4 5 7 6 5 4 3 2 1 3,5-dichloro-3-methylheptane

Guide to Drawing Alkane Formulas Draw the main chain of carbon atoms 1 Number the chain and place the modifiers on the carbons indicated by the numbers 2 Add the correct number of hydrogen atoms to give four bonds to each carbon atom 3

Learning Check Draw the condensed structural formula for 3-bromo-1-chlorobutane.

Solution 3-bromo-1-chlorobutane 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 4 3 2 1 STEP 3: Add hydrogen to complete 4 bonds to each C. CH3─CH─CH2─CH2─Cl

Naming Cycloalkanes with Substituents The name of a substituent is placed in front of the cycloalkane name. methylcyclobutane CH3 chlorocyclopentane Cl

Learning Check Name each of the following. 1. CH3 CH2─CH3 2.

Learning Check Answers Name each of the following. 1. CH3 CH2─CH3 2. methylcyclopropane ethylcyclohexane

Alkyl Halides Alkyl halides are organohalogens that have the halogen atom attached to an alkyl group. They are represented by R–X branch halogen

Naming Alkyl Halides CH3Br CH3CHBrCH2Br bromomethane (methyl bromide) 1,2-dibromopropane CHCl3 trichloromethane (chloroform) CH2Cl2 dichloromethane (methylene chloride) CCl4 tetrachloromethane (carbon tetrachloride)

Properties of Alkanes

Some Properties of Alkanes Alkanes are nonpolar. insoluble in water. less dense than water. flammable in air.

Gulf Oil Spill

Some Properties of Alkanes Alkanes with 1-4 carbon atoms are methane, ethane, propane, and butane. gases at room temperature. used as heating fuels.

Some Properties of Alkanes 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.

Some Properties of Alkanes 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.

Combustion In combustion reactions, alkanes react with oxygen. CO2, H2O, and energy are produced. Alkane + O2 CO2 + H2O + heat

Functional Groups

Elements in Organic Compounds In organic molecules, carbon atoms bond with four bonds. mostly with H and other C atoms. sometimes to O, N, S. sometimes to halogens F, Cl, and Br. Copyright © 2009 by Pearson Education, Inc.

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

Alkenes, Alkynes, and Aromatic Compounds Alkenes contain a double bond between adjacent carbon atoms. Alkynes contain a triple bond. Aromatic compounds contain a ring of six carbon atoms called benzene. An alkene (olefins) An alkyne (acetylenes) An aromatic (benzenes)

Comparing Alkenes, Alkynes, and Aromatic Compounds

Alcohols and Ethers An alcohol contains the hydroxyl (-OH) functional group. A thiol contains the thiol (-SH) functional group. An ether contains an oxygen atom bonded to two carbon atoms.

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

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

Amines and Amides In amines, the functional group is a nitrogen atom. | —N — In amides, the hydroxyl group of a carboxylic acid is replaced by a nitrogen group. Amines An amide

Summary of Functional Groups

The End

End of Chapter Learning Checks Try these after you have reviewed the chapter

Learning Check Write the formula for an alkane that has nine carbon atoms. Write the condensed structural formula for the straight-chain alkane that has nine carbon atoms. 72

Learning Check Answers Write the formula for an alkane that has nine carbon atoms. CnH2n+2 = C9H20 Write the condensed structural formula for the straight-chain alkane that has nine carbon atoms. CH3CH2CH2CH2CH2CH2CH2CH2CH3 73

Learning Check Give the IUPAC name for the this alkane.

Learning Check Answers Give the IUPAC name for the this alkane. 6 5 4 3 2 1 2-methylhexane

Learning Check Write the structural formula for 5-ethyl-3-methyloctane.

Learning Check Answers Write the structural formula for 5-ethyl-3-methyloctane. 3 8 7 6 5 4 2 1

Learning Check Classify the following reaction as substitution, elimination or addition. 78

Learning Check Answers Classify the following reaction as substitution, elimination or addition. Elimination 79

Learning Check Write structural formulas for: 1-bromo-2-methylcyclopentane and 1,1-dichloro-3-ethylcyclohexane. 80

Learning Check Answers Write structural formulas for 1-bromo-2-methylcyclopentane and 1,1-dichloro-3-ethylcyclohexane. 1,1-dichloro-3-ethylcyclohexane 1-bromo-2-methylcyclopentane 81