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Chapter Outline
Chapter 19
Introduction to General, Organic, and Biochemistry, 10e John Wiley & Sons, Inc
Morris Hein, Scott Pattison, and Susan Arena
Organic Chemistry: Saturated Hydrocarbons
Organic chemistry is important in nanotechnology. A carbon nanotube forest is shown here.
Chapter Outline
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Chapter Outline
19.1 Organic Chemistry: History and Scope
19.2 The Carbon Atom: Bonding and Shape
19.3 Organic Formulas and Molecular Models
19.4 Classifying Organic Compounds
19.5 Hydrocarbons
19.6 Saturated Hydrocarbons: Alkanes
19.7 Carbon Bonding in Alkanes
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19.8 Isomerism
19.9 Naming Organic Compounds
19.10 Introduction to the Reactions of Carbon
19.11 Reactions of Alkanes
19.12 Sources of Alkanes
19.13 Gasoline: A Major Petroleum Product
19.14 Cycloalkanes
Chapter 19 Summary
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Organic chemistry is the study of compounds containing carbon.
These compounds occur naturally but can be prepared in a
laboratory. The early history of organic chemistry included an
erroneous theory. (i.e. that organic compounds exist only in living organisms).
The German chemist Wöhler disproved this theory in
1828 with the laboratory synthesis of urea.
Organic Chemistry: History and Scope
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Carbon can form a vast array of long chain and ring containing compounds because carbon has the unique ability to bond to itself.
Organic compounds include drugs, fuels, toiletries, plastics,
and fabrics. You can see why organic chemistry is such an important field of study.
What is organic chemistry?
Lipstick is made of organic molecules. Cosmetics and perfumes contain organic compounds.
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The Carbon Atom: Bonding and Shape
Carbon can form saturated compounds (i.e. where all carbon atoms have four single bonds) or unsaturated compounds (i.e. at least one carbon has a double bond (C=C) or a triple bond (C≡C)).
Ethane is a saturated hydrocarbon because it has all single bonds.
Ethene is an unsaturated hydrocarbon because it has a double bond.
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Carbons with double bonds have a triangularor trigonal planar shape.
Carbons with triple bonds are linear.
Carbons with four single bondshave a tetrahedral shape.
These are the molecular shapes of carbon compounds predicted by the VSEPR Bonding Theory.
The Carbon Atom: Bonding and Shape
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Figure 19.1 Tetrahedral structure of carbon: (a) a regular tetrahedron; (b) a carbon atom with tetrahedral bonds; (c) a carbon atom within a regular tetrahedron; (d) a methane molecule, CH4
This figure shows the bonding shape that results when carbon has four single bonds.
The Carbon Atom: Bonding and Shape
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Estimate the bond angles around 1C and 2C in the following structure.
Your Turn!
1C C
H
H
H
C
H
2CH
H
H
H
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Estimate the bond angles around 1C and 2C in the following structure.
Your Turn!
1C C
H
H
H
C
H
2CH
H
H
H
109.5o
120o
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Organic Formulas and Molecular Models
or in the case of a model.
Structural formulas or models are often used in organic chemistry to illustrate molecules.
For example,
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Lewis structure Structural formula Condensed structural formula
Line structure Ball-and-stick model Space-f illng model
Figure 19.3 Types of formulas and models used to represent organic molecules. Each diagram is a representation of a propane molecule.
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( condensed structural f ormula)
( line structure)
This is an example of how to change a condensed structural formula into a line structure.
The table on the next slide summarize formulas and models used in organic chemistry.
Organic Formulas and Molecular Models
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Lewis structure Structural formula Condensed structural formula Line structure Ball-and-stick model Space-filling model
Shows all bonds, all atoms, and all nonbonding electrons Same as Lewis structure except nonbonding electrons are not shown
Bonds are collapsed so relative positions of atoms are group together Only bonds and functional groups are shown and each endpoint and bend represents a carbon atom Atoms are shown as balls and bonds as sticks and the shape is shown at the central atom. Bonds are omitted and the size of atoms are emphasized.
Formula or model Definition
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Classifying Organic Compounds
Functional groups are group of atoms (or one atom) that have specific behavioral characteristics in organic compounds.
Organic compounds are classified based on the functional
groups that they contain.
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Classifying Organic Compounds
The list of common functional groups found in organic compounds are shown here on Table 19.1.
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Classifying Organic Compounds
The list of important functional groups found in biological compounds is shown here on Table 19.2.
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Ethanol contains the alcohol functional group and dimethyl ether contains the ether functional group. They have the same molecular formula but the boiling point (b.p.) of ethanol is 78°C while the b.p. of dimethyl ether is -23°C because of the structural differences between the molecules.
Classifying Organic Compounds
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Hydrocarbons Hydrocarbons are organic compounds that contain only
carbon and hydrogen atoms. (e.g. propane, CH3CH2CH3 is a hydrocarbon but ethanol, CH3CH2OH is not).
Hydrocarbons are classified as either aliphatic (i.e those
hydrocarbons without benzene rings in the chemical structure) or aromatic.(i.e those hydrocarbons with benzene rings in the chemical structure) as shown in Figure 19.4 on the next slide.
Hydrocarbons are also classified as saturated or unsaturated
compounds.
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Figure 19.4 Classes of Hydrocarbons
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The principal source of hydrocarbons is fossil fuels which include natural gas, petroleum, and coal.
Fossil fuels are the primary source of heat and also a
primary source of organic chemicals.
Hydrocarbons
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Alkanes are saturated hydrocarbons that are either straight- chain or branched-chain hydrocarbons.
Saturated Hydrocarbons: Alkanes
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Alkanes form a homologous series of straight-chain molecules as seen in Table 19.3 on the next slide. Members of a homologous series have similar structures but different chemical formulas.
The general formula for all non-cyclic alkanes is shown here.
Saturated Hydrocarbons: Alkanes
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Saturated Hydrocarbons: Alkanes
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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.
Your Turn!
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Your Turn!
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
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Alkanes contain saturated carbon atoms that have four sigma bonds.
Sigma bonds are linear bonds formed by a pair of electrons in overlapping atomic orbitals.
C
H
H H
H
methane( an alkane)
Each C-H sigma bond is formed by overlap of H1s and Csp3 orbitals
Carbon Bonding in Alkanes
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Carbon has the ability to form four sigma bonds because of its ability to hybridize its valence shell electron orbitals (i.e the s and the 2p orbitals) as shown in Figure 19.5 on the next slide.
Carbon Bonding in Alkanes
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Figure 19.5 Rearrangement of carbon 2s and 2p orbitals to form four equivalent sp3 hybrid orbitals.
Carbon Bonding in Alkanes
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Figure 19.6 (a) A single sp3-hybridized orbital; (b) four sp3-hybridized orbitals in a tetrahedral arrangement; (c) sp3 and s orbitals overlapping to form four C-H sigma bonds in methane.
Carbon Bonding in Alkanes
Figure 19.6 shows the tetrahedral nature of the sp3-hybridized orbitals.
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Isomerism
The properties of an organic substance are dependent on its molecular structure. The majority of organic compounds are made up of relatively few elements: carbon, hydrogen, oxygen, nitrogen, and the halogens.
The valence bonds or points of attachment may be represented in structural formulas by a corresponding number of dashes attached to each atom.
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Carbon can form four single bonds each, nitrogen can form three single bonds, oxygen can only form two single bonds, and hydrogen and the halogens can form one single bond each.
Isomerism
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Because carbon can form four single bonds, alkanes with four or more carbon atoms can form isomers.
Isomers are molecules that have the same molecular formula
but different structural formula.
Isomerism
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For example, it is possible to write two structural formulas corresponding to the molecular formula C4H10 (i.e., butane and isobutane are isomers of each other). Notice the ball-and-stick models of these molecules on the next slide.
Isomerism
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Figure 19.7 Ball-and-stick models illustrating the structural formulas of several alkanes.
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There are several isomers of heptane, C7H16. Draw structural formulas and condensed structural formulas for the two isomers that only have one branching methyl group.
Your Turn!
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37
Your Turn!
H C
H
H
C
CH3
H
C
H
H
C
H
H
C
H
H
C
H
H
H (CH3)2CHCH2CH2CH2CH3
H C
H
H
C
H
H
C
CH3
H
C
H
H
C
H
H
C
H
H
HCH3CH2CHCH3CH2CH2CH3
There are several isomers of heptane, C7H16. Draw structural formulas and condensed structural formulas for the two isomers that only have one branching methyl group.
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How do chemists name organic compounds? Organic compounds are named using the IUPAC System
(International Union of Pure and Applied Chemistry). The IUPAC System was developed at an international
science meeting in Geneva in 1892. The IUPAC System is essentially a set of rules that allow
for a systematic and uniform method of naming compounds.
Naming Organic Compounds
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Alkyl groups have one hydrogen less than the respective alkane.
C
H
H H
H
methane
C
H
H
H
methyl
remove H
( an alkane) (an alkyl group)
The general formula for alkyl groups is shown here and a list of alkyl groups are shown in Table 19.4.
Naming Alkyl Groups
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Naming Alkyl Groups
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Carbon atoms are often classified based on the number of carbon atoms directly attached to them.
Primary (1°) Secondary (2°) Tertiary (3°)
A carbon with one carbon attached A carbon with two carbons attached A carbon with three carbons attached
Naming Organic Compounds
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Here is an example of a molecule with all three types of carbon atoms.
Naming Organic Compounds
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Identify all the carbon atoms in the structure below as 1o, 2o or 3o.
Your Turn!
H C
H
H
C
H
H
C
CH3
CH3
OH
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Identify all the carbon atoms in the structure below as 1o, 2o or 3o.
Your Turn!
H C
H
H
C
H
H
C
CH3
CH3
OH1o 2o 3o
1o
1o
Chapter Outline
1. Identify and then name the longest continuous chain of carbon atoms. The longest chain in this molecule contains six carbon atoms.
IUPAC Rules for Naming Alkanes
45
Chapter Outline
2. Number the chain so any branch alkyl groups have the lowest possible number. There is only one correct way to number the carbon atoms in the longest chain.
6
54 3 2 1 Numbering in this direction is incorrect because
it gives the methyl branch a higher number, i.e. a 4 instead of a 3.
IUPAC Rules for Naming Alkanes
46
Chapter Outline
3. The methyl group is attached to the #3 carbon atom not the #4 carbon atom. The IUPAC name for the molecule is 3-methylhexane.
6
54 3 2 1 Numbering in this direction is incorrect because
it gives the methyl branch a higher number, i.e. a 4 instead of a 3.
IUPAC Rules for Naming Alkanes
47
Chapter Outline
4. Use prefixes (i.e. di, tri, tetra etc. ) if two or more of the same alkyl group branches appear on the longest chain. One methyl group is on the #2 carbon atom and another methyl group is on the #3 carbon atom.
IUPAC Rules for Naming Alkanes
48
Chapter Outline
5. When several different groups are attached to the same parent compound, list the groups in alphabetical order (e.g. chloro is listed before isopropyl and isopropyl is listed before methyl).
IUPAC Rules for Naming Alkanes
49
Chapter Outline
Give the IUPAC name for the this alkane.
Your Turn!
50
Chapter Outline
Give the IUPAC name for the this alkane.
2-methylhexane
Your Turn!
51
Chapter Outline
Write the structural formula for 5-ethyl-3-methyloctane.
Your Turn!
52
Chapter Outline
Write the structural formula for 5-ethyl-3-methyloctane.
Your Turn!
53
Chapter Outline
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The importance of organic chemistry is illustrated by the variety of reactions that occur at the carbon atom which include four major types.
• Oxidation-reduction • Substitution • Addition • Elimination
Introduction to the Reactions of Carbon
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Oxidation involves a higher number of oxygen atoms bonding to carbon. Carbon dioxide is more oxidized than methane so this is an oxidation reaction.
Introduction to the Reactions of Carbon
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Reduction is the reverse of oxidation and involves a higher number of hydrogen atoms bonding to carbon. Methanol is more reduced than carbon dioxide so this is a reduction.
Introduction to the Reactions of Carbon
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Substitution is the exchange of one atom for another at the carbon atom.
In this reaction a bromine atom changes position with a
hydrogen atom in methane.
Introduction to the Reactions of Carbon
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Addition is a reaction where two reactants join to form a single product.
Introduction to the Reactions of Carbon
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Elimination is the splitting of a single reactant into two products.
Introduction to the Reactions of Carbon
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60
Classify the following reaction as substitution, elimination or addition.
Your Turn!
H C
H
H
C
H
H
C
Cl
H
H C C
H
+ HCl
C
H
H
H
H
H
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Classify the following reaction as substitution, elimination or addition.
Your Turn!
H C
H
H
C
H
H
C
Cl
H
H C C
H
+ HCl
C
H
H
H
H
H
Elimination
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Oxidation Substitution Elimination Decomposition Rearrangement
Combustion Halogenation Dehydrogenation Cracking Isomerization
Reaction Class Name of Reaction
Reactions of alkanes can be classified as shown in this table.
Reactions of Alkanes
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Combustion (oxidation) Alkanes are a valuable energy source due to their ability to
react with oxygen . Alkanes release a large amount of energy as shown here.
Alkanes generally are considered to be unreactive and for reactions other than combustion a catalyst or other special reaction conditions are necessary.
Reactions of Alkanes
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Halogenation (substitution): Here a chlorine atom is replacing a hydrogen atom on an ethane molecule.
Reactions of Alkanes
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Dehydrogenation (elimination): Here two hydrogen atoms are removed from a propane molecule to form propene.
Reactions of Alkanes
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Cracking (decomposition): Here an alkane undergoes decomposition to form a smaller alkane and an alkene.
Reactions of Alkanes
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Isomerization (rearrangement): Here an unbranched alkane (pentane) undergoes isomerization to form a branched compound that is an isomer of pentane (2-methylbutane).
Reactions of Alkanes
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The chlorination of methane with excess chlorine can produce each of the compounds shown in Table 19.5.
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Alkyl halides are compounds that have an X (X = -F (fluoro), -Cl (chloro), -Br (bromo), or - I (iodo) attached to a carbon atom.
RX is the general formula for alkyl halides.
Reactions of Alkanes
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Examples of Alkyl Halides
Reactions of Alkanes
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71
The mechanism of halogenation consists of three steps: initiation, propagation, and termination as shown on the next few slides.
A mechanism is the individual steps that lead to the product
from the reactant.
Overall Reaction
Reactions of Alkanes
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72
Step I Initiation: Formation of chlorine free radicals.
Reactions of Alkanes
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73
Step II Propagation: A chlorine free radical reacts with the alkane to form hydrogen chloride and an alkyl free radical. The alkyl free radical reacts with a molecule of chlorine to form another chlorine free radical and an alkyl halide.
Reactions of Alkanes
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Step III Termination: 1) The reaction of two chlorine free radicals; 2) the reaction of a chlorine free radical and an alkyl free radical to form an alky halide; 3) the reaction of two alkyl free radicals to form a larger alkane.
Reactions of Alkanes
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Experimental results show that tertiary (3o) free radicals are the most stable and the most easily formed radicals in chemical reactions.
Free Radical Stability and Reactivity
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76
Secondary (2o) free-radicals are next in stability and primary (1o) free radicals are the least stable.
Free Radical Stability and Reactivity
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77
Therefore the major product formed in the chlorination of propane corresponds to the secondary free radical, i.e. 2-chloropropane. The minor product corresponds to the primary free radical.
Free Radical Stability and Reactivity
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78
Write an equation for each step in the free-radical mechanism forming 2-chlorobutane.
Your Turn!
Chapter Outline
79
Write an equation for each step in the free-radical mechanism forming 2-chlorobutane.
Your Turn!
Cl ClUVlight
Cl2
Initiation
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80
Write an equation for each step in the free-radical mechanism forming 2-chlorobutane.
Your Turn!
Propagation
Cl + CH3CH2CH2CH3 HCl + CH3CHCH2CH3
CH3CHCH2CH3 + Cl Cl CH3CHCH2CH3
Cl
+ Cl
Chapter Outline
81
Write an equation for each step in the free-radical mechanism forming 2-chlorobutane.
Your Turn!
Termination
Cl ClCl2
Cl +
CH3CHCH2CH3
CH3CHCH2CH3 CH3CHCH2CH3
Cl
+ CH3CHCH2CH3CH3CHCH2CH3
CH3CHCH2CH3
Chapter Outline
82
• Alkanes are produced from natural gas and petroleum.
• Natural gas and petroleum are formed by the decay of plants and animals
• Natural gas and petroleum are non-renewable
sources of energy.
Sources of Alkanes
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83
The octane rating of gasoline is the knocking performance based on the percent isooctane in an isooctane/heptane mixture. (higher octane ratings = less knocking)
Gasoline is a mixture of hydrocarbons. Without additives it causes knocking which is a detonation of the air-fuel mixture in an engine.
Figure 19.8 Uses of petroleum
Gasoline: A Major Petroleum Product
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84
Manufacturers of gasoline have switched from tetraethyl lead to more environmentally friendly additives like MTBE (methyl-tert-butyl ether) and ethanol.
Gasoline: A Major Petroleum Product
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85
These additives boost octane ratings like lead additives but are better for the environment. However studies have shown that MTBE can pollute ground water and is also being replaced.
Gasoline: A Major Petroleum Product
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86
Cycloalkanes are cyclic alkanes with the general formula CnH2n.
Cycloalkanes
Chapter Outline
87
The physical properties and the chemical reactivity of cycloalkanes are similar to their open-chain counterparts (the alkanes) with two exceptions. Cyclopropane and cyclobutane are more reactive.
Cycloalkanes
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88
Cyclopropane and cyclobutane have higher reactivity because their bonds are strained. The basis for the strain is the deviation of their bond angles from the normal tetrahedral carbon bond angle of 109.5°.
Cycloalkanes
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89
These molecules cannot change shape to significantly change their bond angles like cycloalkanes that have larger ring sizes.
Cycloalkanes
Chapter Outline
90
The result of the bond strain in cyclopropane is that it reacts readily with molecules like bromine as shown here.
Cycloalkanes
Chapter Outline
91
Figure 19.10 Ball-and-stick models of cyclopropane, hexane, and cyclohexane. In cyclopropane, all the carbon atoms are in one plane (bond angles = 60° instead of 109.5° ).
Chapter Outline
92
The cyclohexane molecule is puckered (as shown in the chair conformation) with bond angles about 109.5° as found in hexane.
Chapter Outline
93
Cyclohexane can exist in either the chair or boat conformation.
A conformation is the three-dimensional spatial arrangement
of the atoms in a molecule.
Cycloalkanes
Chapter Outline
94
Figure 19.11 Conformations of cyclohexane: (a) chair conformation; (b) boat conformation. Axial hydrogens are shown in blue in the chair conformation.
Axial hydrogens are at right angles to the plane of the ring.
Equatorial hydrogens are in the plane of the ring.
Cycloalkanes
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95
When naming monosubstituted cycloalkanes: 1. Name the substituent 2. Name the parent cyclohexane
Both of these structures are the same molecule and have the same name (methylcyclohexane).
methyl + cyclohexane = methylcyclohexane
Cycloalkanes
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96
When naming polysubstituted cycloalkanes. 1. Number the ring (clockwise or counterclockwise)
to give the substituted groups the lowest possible numbers.
2. Name the groups and their locations. 3. Name the parent cyclohexane.
Cycloalkanes
Chapter Outline
97
Cycloalkanes
Chapter Outline
98
Write structural formulas for 1-bromo-2-methylcyclopentane and 1,1-dichloro-3-ethylcyclohexane.
Your Turn!
Chapter Outline
99
Write structural formulas for 1-bromo-2-methylcyclopentane and 1,1-dichloro-3-ethylcyclohexane.
Your Turn!
Br
CH3
1-bromo-2-methylcyclopentane
Chapter Outline
100
Write structural formulas for 1-bromo-2-methylcyclopentane and 1,1-dichloro-3-ethylcyclohexane.
Your Turn!
Cl Cl
CH2CH3
1,1-dichloro-3-ethylcyclohexane
Chapter Outline
101
Organic chemistry is the chemistry of carbon compounds. Alkanes are hydrocarbons that are either saturated (no double or triple bonds) or unsaturated (one or more multiple bonds ). Organic compounds are classified by functional groups which is the smaller part of the molecule that determines the chemical profile of the molecule.
Chapter 19 Summary
Chapter Outline
102
Organic molecules can be represented by ball-and stick models, space-filling models, Lewis structures, line structures, and condensed structural formulas. Saturated carbon atoms are sp3 hybridized which form can four sigma bonds.
Chapter 19 Summary
Chapter Outline
103
Reactions of organic molecules are classified as oxidation-reduction, substitution, elimination, and addition. Alkanes undergo combustion but need special reaction conditions to undergo halogenation, dehydrogenation, cracking, and isomerization.
Chapter 19 Summary
Chapter Outline
104
Cycloalkanes (CnH2n ) exist in conformations with hydrogen on each carbon in axial or equatorial position Cyclopropane and cyclobutane are unusually reactive because of strained bonds. The most stable form of cyclohexane is the chair conformation.
Chapter 19 Summary