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Naming Alkanes
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1. Root name: name of longest continuous C chain (parent chain)• 2 equally long? Choose the one with more branches
2. Number C atoms in chain, starting at end with first branch
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4-ethyl-3,5-dimethyloctane1
2
3
658
74
4-ethyl
3-methyl and 5-methyl = 3,5-dimethyl
Octane
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1. Identify substituents, give each a number (C it is connected to)• Two or more identical substituents: use prefixes (di-,
tri-, tetra-, etc.)2. List substituents alphabetically before root name
• Do not alphabetize prefixes3. Punctuation: commas separate numbers from
each otherhyphens separate numbers from
namesno space between last substituent
& root name
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isopropyl
isobutyl
sec-butyl
tert-butyl
alphabetized as “i”
alphabetized as “i”
alphabetized as “b”
alphabetized as “b”
CH CH2 CH3
CH3
C CH3
CH3
CH3
CH CH3CH2
CH3
CH CH3
CH3R
R
R
R
R
R
R
R
Remember that R = any carbon chain
“iso” indicates symmetry
3 carbons
4 carbons
2o
2o
Secondary carbon
Tertiary carbon
3o 3o
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HC H
H
H CC C
H H
HHH
CH
HH
2 - methylbutanebutane
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Expanded Structure Line Structure
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H C
C C C
H
H
CH3
CH3HH
H
C
C
H
H
H
H
H
hexane3,3-dimethyl
1 2 3
4
5
61
2
3
456
hexane4,4-dimethyl
Lowest sum of numbers is correct
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Line Structure
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Alkanes are written with structural formulas that are expanded to show each bond (Lewis Structure). condensed to show each carbon atom and
hydrogen atoms attached to that carbon.
Expanded (Lewis) Condensed H
H C H CH4 , methane
H
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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 │ │ │ │ H H H H
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The names of alkanes 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 Structural FormulaMethane 1 CH4
Ethane 2 CH3CH3
Propane 3 CH3CH2CH3
Butane 4 CH3CH2CH2CH3
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Alkanes with 5-10 carbon atoms in a chain use Greek prefixes.Name # Carbons Structural FormulaPentane 5 CH3CH2CH2CH2CH3
Hexane 6 CH3CH2CH2CH2CH2CH3
Heptane 7 CH3CH2CH2CH2CH2CH2CH3
Octane 8 CH3CH2CH2CH2CH2CH2CH2CH3
Nonane 9 CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Know the 1st eight alkanes (name and structure)
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A. Write the condensed formula for: H H H H H
H C C C C C H H H H H HB. What is its molecular formula?
(Gives total # of each atom, does not indicate how they are arranged)
C. What is its name?
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CH3─CH2─CH2─CH2─CH3
C5H12
pentane
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Hexane is an alkane with six carbon atoms in a
continuous chain. has a “zig-zag” look because each carbon atom
is at the center of a tetrahedron. is represented by a ball-and-stick model as
shown below.
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They are cyclic have two hydrogen atoms fewer than the open chain. (remember each carbon has 4 bonds)
are named by using the prefix cyclo- before the name of the alkane chain with the same number of carbon atoms.
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The structural formulas of cycloalkanes are usually represented by geometric figures,
Cyclopropane CH2
CH2 CH2
CyclobutaneCH2 CH2
CH2 CH2
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Cyclopentane CH2
CH2 CH2
CH2 CH2Cyclohexane
CH2
CH2 CH2
CH2 CH2
CH2
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2-methylpropane
or
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On piece of your own paper, draw AND name ALL of the isomers for the following alkanes:
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Formulas isomers
Pentane
Hexane
Heptane
C5H12
C6H14
C7H16
359
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pentane
2-methylbutane
2,2-dimethylpropane
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hexane
2-methylpentane
3-methylpentane
2,3-dimethylbutane
2,2-dimethylbutane
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heptane
2-methylhexane
3-methylhexane
2,2-dimethylpentane
2,3-dimethylpentane
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05/04/23Dr Seemal Jelani Chem-160 23
2,4-dimethylpentane
3,3-dimethylpentane
3-ethylpentane
2,2,3-trimethylbutane
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C5H12
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(Same formula, different structure)
More branching → weaker London dispersion forces
36.0pentane
27.92-methylbutane
9.52,2-dimethylpropane
Boiling point (°C)NameStructure
BP/MP of Linear alkanes > BP/MP of branched alkanes
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Formulas # isomersC4H9IC3H6Cl2C5H11BrC4H8Cl2
4489
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II
II
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1-iodobutane
2-iodo-2-methylbutane
2-iodobutane
1-iodo-2-methylbutane
I
II
I
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Cl
ClCl
Cl
ClClClCl
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1,1-dichloropropane
1,3-dichloropropane
1,2-dichloropropane
2,2-dichloropropane
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BrBr
Br
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Br
1-bromopentane 2-bromopentane
1-bromo-3-methylpentane3-bromopentane
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Br
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Br
Br
Br
1-bromo-2-methylbutane 2-bromo-3-methylbutane
1-bromo-2,2-dimethylbutane 2-bromo-2-methylbutane
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Cl
ClCl
Cl
Cl
ClCl
Cl
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1,1-dichlorobutane 1,2-dichlorobutane
1,3-dichlorobutane 1,4-dichlorobutane
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Cl Cl
Cl
Cl
ClCl
ClCl
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Cl
Cl
2,2-dichlorobutane
1,1-dichlorobutane
2,3-dichlorobutane
1,2-dichloro-2-methylpropane
1,3-dichloro-2-methylpropane
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Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Alkanes are nonpolar. insoluble in water. less dense than water. flammable in air.
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Alkanes with 1-4 carbon atoms are
methane, ethane, propane, and butane.
gases at room temperature.
used as heating fuels.
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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.
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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.
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Combustion exothermic reaction alkanes used as fuel source
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C4H10 + ___ O2 ___ CO2 + ___ H2O4 513/2
Incomplete Combustion with insufficient O2 produces CO• Poor ventilation, cigarettes
C4H10 + ___ O2 ___ CO + ___ H2O4 59/2
CO is poisonous because it binds to the hemoglobin in the blood, preventing the absorption of O2
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In excess oxygen alkanes burn according to the following equation:
CnH2n+2 +(1.5n+0.5)O2 nCO2 +(n+1)H2O This is called complete combustion,
however if there is insufficient oxygen present incomplete combustion can occur.
CnH2n+2 +(n+0.5)O2 n CO +(n+1)H2O With even less oxygen soot is formed.
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In combustion reactions, alkanes react with
oxygen. CO2, H2O and energy
are produced.Alkane + O2 CO2 +
H2O + heat
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Mechanism◦How the reaction occurs through
multiple steps (most reactions actually occur in many steps)
Chain Reaction◦Reactions that occur on their own after
some initiating event Free Radicals
◦Atoms that have one free electron—highly reactive
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Initiation Step◦ Step where a bond is split by heat/light, producing
free radicals Propagation Step
◦ Step where free radicals react with non-radicals, producing more free radicals and continuing the “chain reaction”
Termination Step◦ Step where free radicals react with each other,
producing non-radicals and terminating the “chain reaction”
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Initiation
Propagation
Propagation
Termination
Radical Halogenation of Alkanes
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Mechanism (chain reaction):
Step 1 Cl2 ⇌ Cl· + Cl ·
Step 2 Cl· + CH4 CH3· + HCl
Step 3 CH3· + Cl2 CH3Cl + Cl·
Step 4 Cl· + Cl· Cl2Overall reaction: CH4 + Cl2 CH3Cl + HCl
Halogenated product is a haloalkaneNaming: halogen atom is a substituent, replace –ine ending with –o
-F fluoro -Cl chloro -Br bromo -I iodo
chloromethane
h(Free Radicals)
Why not 1-chloromethane?
Type of Step
CH4 + Cl2 CH3Cl + HCl
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Halogen substitutes for hydrogen in alkane →multiple results
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CH4 CH3Cl CH2Cl2 CHCl3 CCl4
Cl2
Cl2
Cl2
Cl2
CompoundCH3Cl
CH2Cl2CHCl3CCl4
IUPAC NameChloromethaneDichloromethaneTrichloromethaneTetrachloromethane
Common NameMethyl chlorideMethylene chlorideChloroformCarbon tetrachloride
All are liquids at room temperature• Heavy Cl atoms increase LDF• Polar C-Cl bonds – can have polar molecules
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Chemistry: An Intro to General,Organic and Biological Chemistryby Timberlake (Green/Tan Book)
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1 23
4 56
F Cl
F
Cl
IBr
Cl
Br
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5-chloro-2-fluorohexane
2-chloro-5-fluorohexane 2-chloro-4-fluoro-2,3-dimethylpentane
2-bromo-3-ethyl-4-iodopentane 2-bromo-4-chloro-3-isopropylpentane
Two equal numbering options? Number based on alpha order
12
34
5
6
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ClCl
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?
BrBr
+ Cl2 → OR
1-chloropropane 2-chloropropane
+ Br2 → OR
1-bromo-2-methylbutane 2-bromo-2-methylbutane
Remember that any H on the alkane can be replaced by a halogen
ClOR
3-chloropropane?
+ HCl?
?
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BrBr
BrBr
Br
+ Br2 → OR
OROR
1-bromo-2-methylbutane
2-bromo-3-methylbutane
1-bromo-3-methylbutane
1-bromo-2-methylbutane
2-bromo-2-methylbutane