Chapter 12 Alkanesdfard.weebly.com/uploads/1/0/5/3/10533150/ch12_cas.pdfSciences, each 1% loss of...
Transcript of Chapter 12 Alkanesdfard.weebly.com/uploads/1/0/5/3/10533150/ch12_cas.pdfSciences, each 1% loss of...
1Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
12.1 Alkanes
Chapter 12 Alkanes
2Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Alkanes
Alkanes:Contain only C and H.Have only single C—C bonds.Have a general formula of CnH2n +2
.
C Atoms H Atoms Formula1 2(1) + 2 = 4 CH43 2(3) + 2 = 8 C3H86 2(6) + 2 = 14 C6H14
3Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Structural formulas show the arrangement ofatoms in an organic compound.
In expanded structural formulas, all the individual bonds are drawn. In condensed structural formulas, each carbon is written with the H atoms connected to it.
H H| |
H—C— = CH3— —C— = —CH2 —| |H H
Structural Formulas
4Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Line-Bond FormulasBecause each C atom has a tetrahedral arrangement, the geometrical arrangement of carbon atoms is not a straight line.A line-bond formula abbreviates the carbon chain and shows only the zigzag pattern of bonds from carbon atom to carbon atom.
5Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Summary of Formulas
6Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
IUPAC System of Naming Alkanes
The IUPAC (International Union of Pure and Applied Chemistry) establishes the rules for naming organic compounds.Alkanes are named with –ane endings.The first four alkanes are methane, ethane, propane, and butane.The names of longer carbon chains use Greek prefixes such as pent- for 5 C atoms and hex- for 6 C atoms.
7Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Names of Continuous-Chain Alkanes
8Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
A. Give the name of each compound:1) CH3—CH32) CH3—CH2—CH33) CH3—CH2—CH2—CH2—CH2—CH3
B. Write the condensed structural formula of pentane.
9Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
SolutionA. Give the name of each compound:
1) CH3—CH3 ethane2) CH3—CH2—CH3 propane3) CH3—CH2—CH2—CH2—CH2—CH3
hexaneB. Write the condensed structural formula of
pentane.CH3—CH2—CH2—CH2—CH3
10Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. What is the condensed formula forH H H H | | | |
H —C—C—C—C—H| | | |
H H H H
B. What is its molecular formula?C. What is its name?
Learning Check
11Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. CH3—CH2—CH2—CH3
B. C4H10
C. butane
Solution
12Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
ConformationsAs the groups attached to a C-C single bond rotate around the bond, their relative arrangements has different conformations.
13Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Conformations of ButaneRotation of the end CH3- provides different conformations for butane.
14Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Drawing Structures for Butane
15Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning Check
For propane, write the:1) Molecular formula2) Expanded structural formula3) Condensed structural formula
(two conformations)4) Line-bond formula
16Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Solution1) Molecular formula C3H82) Expanded structural formula
H H H| | |
H —C—C—C—H| | |
H H H3) Condensed structural formula (two conformations)
CH3—CH2—CH3 CH3|
CH3—CH24) Line-bond formula or
17Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
12.2 IUPAC Naming System for Alkanes12.3 Drawing Structural Formulas
Chapter 12 Alkanes
CH3 CH3 | |
CH3—CH—CH2—CH—CH3
2,4-dimethylpentane
18Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Branched-Chain Alkanes
In a branched-chain alkane, a side group called a branch or a substituent is attached to a carbon chain.
branch
19Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Classification of Carbon Atoms
Carbon atoms are classified according to the number of attached carbon atoms.Primary (1°) bonds to one carbon atom.Secondary (2°) bonds to two carbon atoms.Tertiary (3°) bonds to three carbon atoms.
CH3|
CH3 —CH2—CH2—CH3 CH3—CH—CH3secondary primary tertiary
20Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
An alkyl group: Is composed of one or more carbon atoms attached to a carbon chain. Is derived from the corresponding alkane by removing one hydrogen. Is named by replacing the –ane ending of the corresponding alkane with –yl.Derived from methane is methyl and from ethane is ethyl.
Alkyl Groups
21Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Alkyl Groups
22Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The names of branched-chain alkanes indicate the groups bonded to the longest carbon chain.
CH3 methyl group on C-3|
CH3—CH2—CH2—CH—CH2—CH3 hexane 6 5 4 3 2 1
3-Methylhexane
Naming Branched-Chain Alkanes
23Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In the IUPAC system:The longest chain is named as the main chain.Any carbon branches use their alkyl names.Each branch is numbered by counting the main chain from the end nearest the first side group.Branches are listed in alphabetical order.
Naming Summary
24Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Give the IUPAC name for each alkane.A. CH3 CH3
| |CH3—CH—CH2—CH—CH3
B. CH2CH3 CH3| |
CH3—CH2—CH—CH2—C—CH2—CH3|
CH3
Learning Check
25Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A. CH3 CH3 | |
CH3—CH—CH2—CH—CH32,4-dimethylpentane
B. CH2CH3 CH3| |
CH3—CH2—CH—CH2—C—CH2—CH3 |
CH3 5-ethyl-3,3-dimethylheptane
Solution
26Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
What Is In A Name?
The structural formula is drawn from the IUPAC name.
2, 4-dimethylhexane
2, 4 dimethyl hexaneLocation of Two CH3- groups 6 carbon main chainbranches on attached with single C-C bondsmain chain
27Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Drawing Structural FormulasDraw the condensed formula of 2-methylpentane1. Draw the main chain of 5 carbon atoms.
C—C—C—C—C2. Add a CH3 branch to C-2 on the main chain.
CH3 |
C—C—C—C—C3. Add hydrogen atoms to give 4 bonds to each C.
CH3|
CH3—CH—CH2—CH2—CH3
28Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Draw the condensed structural formula forA. 2, 3-dimethylbutane
B. 2, 3, 4-trimethylpentane
Learning Check
29Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Write the condensed structural formula forA. 2, 3-dimethylbutane
CH3 CH3| |
CH3—CH—CH—CH3
B. 2, 3, 4-trimethylpentaneCH3 CH3 CH3| | |
CH3—CH—CH—CH—CH3
Solution
30Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The constitutional isomers for C4H10 can be written by first writing the continuous chain. Then remove one CH3 and attach it as a branch.
CH3|
CH3—CH2—CH2—CH3 CH3—CH—CH3Butane 2-Methylpropane
Writing Isomers
31Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Write 3 constitutional isomers of C5H12 and name each.
Learning Check
32Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
CH3—CH2—CH2—CH2—CH3pentane
CH3|
CH3—CH—CH2—CH3 2-methylbutane
CH3|
CH3—C—CH3 2,2-dimethylpropane|
CH3
Solution
33Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
12.4 Haloalkanes
Chapter 12 Alkanes
34Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In a haloalkane, one or more H atoms in an alkane is replaced by a halogen atom.Haloalkanes containing one halogen are named alkyl halides.In IUPAC names, a halogen is named as fluoro, chloro, bromo, or iodo.
CH3Brbromomethane (methyl bromide)Cl|
CH3—CH—CH2—CH3 2-chlorobutane(sec-butyl chloride)
Haloalkanes
35Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Two or more substituents are named in alphabetical order.
Cl Br| |
CH3—CH—CH2—CH—CH2—CH3
4-bromo-2-chlorohexane
Substituents
36Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Naming of Haloalkanes
Methane compounds with two or more chlorine atoms are sometimes named by common names that do not reflect their structures.
37Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The name of this compound is:Cl CH3| |
CH3—CH2—CH—CH2—CH—CH3
1) 2,4-dimethylhexane2) 3-chloro-5-methylhexane3) 4-chloro-2-methylhexane
Learning Check
38Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The name of this compound is:Cl CH3| |
CH3—CH2—CH—CH2—CH—CH3
3) 4-chloro-2-methylhexane
Solution
39Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Give the IUPAC name for each.
A. CH3CH2—F
Br Cl| |
B. CH3—CH—CH—CH3
Learning Check
40Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Give the IUPAC name for each.A. CH3CH2—F fluoroethane
Br Cl| |
B. CH3—CH—CH—CH3
2-bromo-3-chlorobutane
Solution
41Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Halothane is widely used as an anesthetic, which is a compound that decreases the ability of the nerve cells to conduct pain. What is the IUPAC name of halothane?
F Br| |
F—C—C—Cl| |
F H
Learning Check
42Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The IUPAC name is 2-bromo-2-chloro-1,1,1-trifluoroethane.
F Br| |
F—C—C—Cl| |
F H
Solution
43Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
The ozone (O3) layer in the atmosphere absorbs most of the sun’s harmful radiation.Chlorofluorocarbons (CFCs) cause reactions that destroy the ozone layer. CFCs such as Freon-12 (CF2Cl2) have been used in refrigeration, air conditioning, and foam insulation. The use of CFCs in spray cans is no longer allowed.
Chlorofluorocarbons (CFCs)
44Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
In the stratosphere, the CFCs are cleaved by the high-energy UV radiation from the sun.
UV lightCF2Cl2 CF2Cl + Cl
The Cl reacts with ozone (O3). The ClOproduced destroys another O3 forming additional Cl. Thus one Cl can destroy many O3 molecules.
Cl + O3 ClO + O2ClO + O3 Cl + 2O2
Chlorofluorocarbons and Ozone
45Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
According to the National Academy of Sciences, each 1% loss of ozone (O3) increases the amount of UV radiation reaching the earth by 2%. More UV radiation means more skin cancer and cataracts in humans, more intense photochemical smog, and lower crop yields.
Impact of Loss of Ozone
46Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
12.5 Cycloalkanes
Chapter 12 Alkanes
47Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Cycloalkanes: Are rings of carbons that can be drawn as geometric figures. Have a general formula of CnH2n or 2 H less than the alkane. propane C3H8 cyclopropane C3H6.butane C4H10 cyclobutane C4H8. Are named with the prefix cyclo- in front of the corresponding alkane name.
Cycloalkanes
48Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Formulas of Cycloalkanes
49Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
A cycloalkane with:One substitutuent is named by placing the name of the substituent in front of the cycloalkane name.Two or more substitutuents is named by numbering the ring in the direction that gives the lower numbers to the substituents.
Naming Cycloalkanes
50Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Cycloalkanes with Side Groups
CH3
CH3
CH3
CH3
CH3
CH3
methylcyclopentane
1,2-dimethylcyclopentane
1,2,4-trimethylcyclohexane
51Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning CheckName each of the following cycloalkanes.
CH3
CH3
Cl
CH3
Cl
52Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
SolutionName each of the following cycloalkanes.
1,2-dimethylcyclobutane
chlorocyclopentane
1-chloro-3-methylcyclohexane
CH3
CH3
Cl
CH3
Cl
53Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Constitutional IsomersThe rigid ring in a cyclic structure prevents rotation of substitutuents bonded to the ring. A cyclic structure with two substituents has two isomers called cis-trans isomers. The cis isomer, has two substituents on the same side of the ring.The trans isomer, has two substituents on
opposite sides of the ring.
54Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Cis-Trans Isomers
The compound 1,2-dichlorocyclopropane has cis-trans isomers.Cl atoms on Cl atoms onsame side opposite sides
Cl Cl Cl
Clcis-1,2-dichlorocyclopropane ` trans-1,2-dichlorocyclopropane
55Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning CheckName each as a cis or trans isomer.
Br
Br
ClCl
Br
Cl
56Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
SolutionName each as a cis or trans isomer.
trans-1,2-dibromocyclopropane
cis-1,3-dichlorocyclobutane
trans-1-bromo-3-chlorocyclopentane
Br
Br
ClCl
Br
Cl
57Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Chapter 12 Alkanes
12.6 Physical Properties of Alkanes andCycloalkanes
12.7 Chemical Properties of Alkanes andCycloalkanes
58Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Physical Properties of AlkanesAlkanes, including cycloalkanes:
Are nonpolar and insoluble in water.Have densities between 0.65 – 0.70 g/mL; they float on water.Have low melting and boiling points compared to other families of organic compounds.
59Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Boiling Points of AlkanesBoiling points:
Increase in larger alkane molecules due to increased dispersion forces.Are lower for branched alkanes because they have fewer contact points.Are higher for cycloalkanes because their rigid structures allow more contact and attraction between molecules.
60Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Boiling Points of Pentanes
61Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Uses of AlkanesMethane, ethane, propane, and butane are gases at room temperature and used as fuels.Alkanes with 5-17 carbon atoms are liquids and found in gasoline, diesel, and jet fuels.Alkanes with 18 or more carbon atoms are solids and found in the waxy coatings of fruits and vegetables.
62Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Crude OilThe differences in boiling points are used to separate hydrocarbons in crude oil. Heating to higher temperatures produces gases that are removed and cooled.
63Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Alkanes are typically not very reactive due to strong C-C single bonds.The most typical reaction is combustion, where an alkane reacts with oxygen to produce carbon dioxide, water, and energy.
alkane + O2 CO2 + H2O + energy
Chemical Properties of Alkanes
64Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
CombustionA fuel such as propane reacts with oxygen and burns, producing CO2 and H2O.Propane is burned to obtain energy and heat for cooking or warming a room.
C3H8 + 5O2 3CO2 + 4H2O
65Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Step 1 Write the reactants and products. C3H8 + O2 CO2 + H2O
Step 2 Balance C.C3H8 + O2 3CO2 + H2O
Step 3 Balance H.C3H8 + O2 3CO2 + 4H2O
Step 4 Balance O with O2.
C3H8 + 5O2 3 CO2 + 4H2O
Steps in Balancing a Combustion Equation
66Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Complete and balance the reaction for the complete combustion of C7H16.
Learning Check
67Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Step 1
C7H16 + O2 CO2 + H2O
Step 2 and 3
C7H16 + O2 7CO2 + 8H2O
Step 4
C7H16 + 11O2 7CO2 + 8H2O
Solution
68Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Write the combustion reaction for ethane and balance.
Learning Check
69Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Write the combustion reaction for ethane and balance.ethane CH3—CH3 = C2H6
C2H6 + 7/2 O2 2CO2 + 3H2O
Multiply through by 2 to clear 7/2 2C2H6 + 7O2 4CO2 + 6H2O
Solution
70Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Halogenation of Alkanes(Substitution)
When alkanes react with halogens, a mixture of halogenated products is produced. In a reaction called substitution, one or more H atoms are replaced with a halogen usually Cl or Br.The equation for the reaction of ethane and chlorine to give the monosubstituted product is CH3—CH3 + Cl2 CH3—CH2—Cl + HCl
71Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
Learning CheckGive the structures and names of the monosubstituted products for the reaction of propane with bromine in the presence of light.
72Copyright © 2004 Pearson Education Inc., publishing as Benjamin Cummings.
SolutionGive the structures and names of the monosubstituted products for the reaction of propane with bromine in the presence of light.CH3—CH2—CH2— Br
1-bromopropane; propyl bromideBr|
CH3—CH—CH32-bromopropane; isopropyl bromide