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Chapter 6 Organic Chemistry
Copyright ©2019 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.
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Carbon The world contains millions of known compounds, and 95% of them have carbon in common What is so special about carbon? Figure 6.1; page 140
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Carbon (continued) Smallest member and the only nonmetal of group 4A
Forms four covalent bonds Forms single, double, and triple bonds Bonds to itself, forming chains, rings, and branched structures Figure on top is from page 140 Figure at the bottom, page 141
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Organic Chemistry Study of carbon-containing compounds and their chemistry In early 1800s, scientists knew that chemical compounds were of two types Organic compounds Came from living organisms and were chemically fragile Easily decomposed with heat Inorganic compounds Came from the earth and were chemically durable Successfully synthesized by 19th-century chemists
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Urea Synthesized by Friedrich Wohler in 1828
Organic compound but was synthesized from an inorganic compound Subsequent death of vitalism The idea that life was somehow beyond physical laws was proven wrong Idea that living organisms must follow the physical laws of the universe came into being Figure 6.3; page 142
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Types of Organic Compounds
Hydrocarbons Contain only carbon and hydrogen Functionalized hydrocarbons Hydrocarbons that contain additional atoms or groups of atoms called functional groups Hydrocarbon family can be further divided into subfamilies
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Figure 6.4: Organic Compounds
Figure 6.4, page 143
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Alkanes All carbon atoms connected by single bonds
General molecular formula: CnH2n+2 Simplest alkane: Methane, CH4 Carbon forms four single covalent bonds with four hydrogen atoms Carbon atom attains an octet Each hydrogen atom attains a duet Methane molecule is stable Figure on top is from page 143 Figure at the bottom is from page 143
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Alkanes (continued) Example of larger alkanes
Figure on the left is from page 144 Figure on the right is from page 144
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Polarity of Hydrocarbons
Carbon and hydrogen that compose methane have only slightly different electronegativities, making the bonds between them mostly nonpolar Any slight polarity present in each bond is canceled by the tetrahedral shape of the molecule Every other hydrocarbon is also nonpolar Hydrocarbons are unable to mix with polar substances such as water
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Structural Formulas Show the relative positions of atoms in a molecule
Two-dimensional Similar to Lewis structures, but dashes represent bonding electron pairs
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Structural Formulas (continued)
Condensed structural formulas are compactly written structural formulas Example: Ethane (C2H6) Figure is from page 144
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Propane Formulas Figure 6.5; page 144
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Naming Alkanes Straight-chain alkanes are named with a base name, reflecting the number of carbon atoms in the longest continuous chain and using the suffix -ane. Table 6.2; page 146
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Table 6.1: Alkanes Table 6.1; page 145 15
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Table 6.1: Alkanes (continued)
Table 6.1; page 145 16
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Concept Check 6.1 Give the molecular, structural, and condensed formulas for the straight-chained alkanes with seven and eight carbons and name them.
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Concept Check 6.1 Solution
C7H16: Heptane C8H18: Octane
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Properties of Alkanes Flammability Nonpolarity
CH3CH2CH3 + 5 O2 > 3 CO2 +4 H2O Combustion reaction: Carbon-containing compound reacts with oxygen to form carbon dioxide and water Nonpolarity Table 6.3; page 147 19
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Alkenes and Alkynes Unsaturated hydrocarbons
Contain at least one double or triple bond, respectively Have fewer hydrogen atoms per carbon atom than alkanes
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Alkenes Flammable and nonpolar like alkanes
Double bond makes them susceptible to the addition of other atoms The name of an alkene is derived from the corresponding alkane by changing the -ane ending to -ene Picture of bananas from page 149
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Concept Check 6.2 Draw the structural formula for 1-hexene.
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Concept Check 6.2 Solution
The “hex-” prefix indicates that there are six carbons. The -ene ending indicates that it is an alkene (contains a carbon–carbon double bond).
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Concept Check 6.2 Solution (continued)
“1” indicates the position where the double bond begins (on carbon #1), with the longest continuous carbon chain numbered from the end giving the double bond the lowest number.
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Table 6.4: Alkenes Table 6.4; page 148
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Alkynes Alkynes can be derived from alkenes by removing two additional hydrogen atoms from the two carbon atoms on either side of the double bond and placing a triple bond between them Ethyne (acetylene) is used in welding torches Most of the other alkynes are not commonly encountered directly except as minor components of gasoline
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Table 6.5: Alkynes Table 6.5; page 150
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Concept Check 6.3 Draw the structural formula for 1-hexyne.
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Concept Check 6.3 Solution
The “hex-” prefix indicates that there are six carbons. The -yne ending indicates that it is an alkene (contains a carbon–carbon triple bond). “1” indicates that the triple bond begins on carbon #1, with the longest continuous carbon chain numbered from the end giving the triple bond the lowest number.
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Isomers Molecules having the same molecular formula but different structures Differ in their properties and can be distinguished by inspecting their structural formulas Both the figures are from page 150
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Isomers (continued 1) Alkenes and alkynes exhibit isomerism based on the position of the double or triple bond Example: Double bond in butane can be in two different positions Figure is from page 151.
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Isomers (continued 2) Have radically different properties from each other Nature can take the two atoms and make two different molecules with drastically different properties and functions One of them, progesterone, makes pregnancy possible; the other, THC, alters the way the brain processes stimuli
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International Union of Pure and Applied Chemistry (IUPAC) Recommendations for Naming Hydrocarbons
Alkanes Determine the base name after selecting the longest continuous chain and counting the number of carbon atoms in it Consider branches as substituents of the base chain Number the base chain beginning with the end closest to the first branch and assign a number to each substituent
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Write the name in the following order:
International Union of Pure and Applied Chemistry (IUPAC) Recommendations for Naming Hydrocarbons (continued) Write the name in the following order: Number of the substituent followed by a dash Name of the substituent Base name of the compound
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Concept Check 6.4 Name the following alkane:
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Concept Check 6.4 Solution
The longest continuous carbon chain has six carbons and is named hexane. It is numbered from the end giving the substituent the lowest possible number. Methyl substituent is located on carbon #3. The compound is named 3-methylhexane.
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Additional IUPAC Rules
When two or more substituents are present, number each and list them alphabetically Use a numbering system that contains the lowest possible numbers When two or more substituents are on the same carbon, use that number twice Use prefixes to denote identical substituents, and separate the numbers indicating their positions from each other using a comma 37
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Concept Check 6.5 Name the following alkane:
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Concept Check 6.5 Solution
Heptane is the longest continuous carbon chain. Two methyls and an ethyl are branching substituents.
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Concept Check 6.5 Solution (continued)
Substituents are named 5-ethyl and 2,2-dimethyl according to their positions on the chain, then are listed alphabetically in the name.
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Naming Alkenes and Alkynes
Named similar to alkanes, except for the addition of a number at the beginning to indicate the position of the multiple bonds and a change from -ane to -ene or -yne in the base name The base chain is numbered to give the multiple bond the lowest possible number
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Naming Alkenes and Alkynes (continued)
Name the following compounds: 1-butene 2-pentyne 4-methyl-2-pentene 5-ethyl-3-heptyne
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Kekulé Early structure elucidation
Carbon’s tendency toward four bonds Dreamed that he saw chains of six carbon atoms as snakes One snake bit its own tail Proposed benzene as a ring of six carbon atoms with alternating single and double bonds after being stimulated by his dream Structure is still accepted today with a minor modification
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Update on Kekulé’s Benzene Ring
Kekulé proposed a ring containing alternating double and single bonds The bonds in benzene have the same length due to resonance Each bond is now considered to be midway between a double and a single bond Graphic from page 155
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Update on Kekulé’s Benzene Ring (continued)
Structure of benzene is drawn as a hexagon with a circle inside it Figure is from page 156.
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The Benzene Ring Particularly stable and is found in many organic molecules When the ring contains substituents, it is called a phenyl ring Also called aromatic ring because of the notable aroma of many compounds containing such a ring Two or more such rings fused together make polycyclic aromatic hydrocarbons
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Common Examples Top and Bottom figures are from page 157
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Functionalized Hydrocarbons
Basic hydrocarbon structures form the foundation of a major grouping of organic compounds known as functionalized hydrocarbons Graphic from page 158
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Functionalized Hydrocarbons (continued)
Contain additional atoms or groups of atoms called functional groups incorporated into their structure Insertion of functional groups into a hydrocarbon alters its properties Example of a functional group: —OH in ethanol All compounds containing the same functional group form a family Have characteristic properties associated with that functional group
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Representing Functionality
Generic symbolism is R—FG, where R is the hydrocarbon part of the molecule and FG is the functional group Symbol for alcohol is R—OH Functional groups help organize and classify organic compounds in a systematic way
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Table 6.6: Functionalized Hydrocarbons
Table 6.6; page 158
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Concept Check 6.6 For the following compound, identify the functional group and the name of its family.
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Concept Check 6.6 Solution
For the following compound, identify the functional group and the name of its family.
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Chlorinated Hydrocarbons
Found in pesticides, solvents, and refrigerant liquids Have one or more chlorine atoms substituting for one or more hydrogen atoms Have the general formula R–Cl Addition of chlorine to a hydrocarbon tends to lower its flammability and chemical reactivity Figure 6.9, page 159
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Dichlorodiphenyltrichloroethane (DDT)
Paul Muller demonstrated DDT’s effectiveness against insects and relative nontoxicity to humans Dramatically decreased malaria cases in many countries Muller was awarded Nobel Prize in 1948 Resistance and bioamplification led to DDT’s ban The American bald eagle was placed on the endangered species list because of DDT. It has made a dramatic comeback since the ban on DDT. Page 159
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Chlorofluorocarbons (CFCs)
Considered a subfamily of chlorinated hydrocarbons and contains fluorine as well as chlorine Chemically stable Eventually drift to the upper atmosphere, where high-energy sunlight breaks a chemical bond and releases a reactive chlorine atom
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Chlorofluorocarbons (CFCs) (continued)
Danger to the ozone layer led to the ban on the use of CFCs Figure 6.10; page 160
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Alcohols General formula: R-OH
Found in alcoholic beverages and in medical antiseptics Presence of —OH causes alcohols to be polar Named according to the name of the hydrocarbon chain modified to end in -ol Figure is from page 161
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Ethanol Alcohol present in alcoholic beverages Gasoline additive
Made by sugar fermentation C6H12O6 → 2 CH3CH2OH + 2 CO2 All alcoholic beverages contain primarily ethanol and water, with a few other minor components Central nervous system (CNS) depressant Could pose adverse health effects Graphic from page 160
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Other Alcohols Substitution of a methyl group for hydrogen in ethanol produces isopropyl alcohol Known as rubbing alcohol Figure is from page 161
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Other Alcohols (continued)
Methanol, which is used as a solvent, is toxic to the human liver Figure is from from page 162
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Aldehydes and Ketones Commonly found in pleasant flavors and aromas
Aldehydes have the general formula RCHO, where the oxygen is joined to the carbon via a double bond Figure is from page 163.
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Aldehydes and Ketones (continued)
Ketones are similar to aldehydes, but instead of one R group, they have two Have the general formula RCOR′ R' means that the second R group could be different from the first
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Formulas Aldehydes Named according to the number of carbon atoms and given the ending -al Methanal (formaldehyde) is the simplest aldehyde Figure is from page 162
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Formulas (continued) Ketones
Similar to aldehydes but have two R groups with carbonyl Names end in -one Acetone is the simplest ketone Major component of fingernail polish remover Graphic from page 162
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Carboxylic Acids Commonly found in sour foods General formula: RCOOH
Simplest carboxylic acid is formic acid (HCOOH) Figure is from page 165
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Esters Have pleasant odors General formula: R—COO—R′
Named according to the relevant R and R′ groups and end with –ate Figure is from page 167
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Ethers Contain the functional group —O—
General formula: R—O—R′, where R and R′ are hydrocarbons Named according to the two hydrocarbon groups and given the ending -ether Simplest ether is dimethyl ether Figure is from page 167
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Amines Organic compounds that contain nitrogen General formula: NR3
Notable for unpleasant odors Named according to R groups present and end in -amine Figure is from page 168
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Concept Check 6.7 Match each of the compounds with the following families: Ketone, aldehyde, ester, carboxylic acid, alcohol, and amine.
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Concept Check 6.7 Solution
The functional groups are circled.
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Chapter Summary Molecular concept Societal impact
Organic compounds versus inorganic Organic compounds make everyday living possible Hydrocarbons include alkanes, alkenes, and alkynes Hydrocarbons are the primary molecules that society uses for fuel Other functional groups Organic functional groups can be recognized in the compounds that are used every day
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