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Chapter 9: ExplosivesA Study of Organic Molecules with Simple
Functional Groups and the Forces within
Them
The Chemistry of Everything
Kimberley Waldron
Richard Jarman,
College of DuPage
©2007 Pearson Prentice Hall 2
Chapter 9 Topics
• Combustion reactions and explosions.
• Endothermic and exothermic reactions.
• Alkanes, alkenes, and alkynes.
• Hydrocarbon nomenclature.
• Cis–trans isomerism.
• Ethers.
• Bond energies.
• High explosives and low explosives.
• Entropy and the second law of thermodynamics.
• Gas chromatography.
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Gunpowder Plot
• Guy Fawkes is a
celebration of organic
chemistry.
• The nucleus provides
huge energy through
nuclear reactions.
• Traditional explosives
have used chemical
reactions.
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Gunpowder
• Gunpowder uses oxidation of carbon.
• The reactants have elements C and S.
• Products contain C and S bound with O.
• The reactants are solids.
• Many of the products are gases.
• Conversion of solid to gas creates blast.
3222324210()11()4()5()5()5()()3()KNOsCsSsCOgCOgNgKCOsKSOsKS+ + + + + + +
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Heat and Expansion
• The gunpowder explosion
is a combustion reaction.
• Reaction between fuel
(sulfur and carbon) and
oxygen produces heat.
• Heat is not sufficient to
produce an explosion.
• The reaction must occur
in confined space.
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The Gunpowder Car?
• The use of explosive energy to power a
vehicle was recognized, but not
successfully realized with gunpowder.
• Internal combustion engines use
explosions to create motion, but use
gasoline instead.
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Gasoline and Carbon: Things
in Common
• Gunpowder and gasoline are fuels.
• Both contain carbon:– Gunpowder contains the element carbon.
– Gasoline is a hydrocarbon that contains C and Hatoms.
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Combustion of
Hydrocarbons• Hydrocarbons combine with oxygen to produce
carbon dioxide and water.
• All the products are gases:
– Carbon dioxide (CO2)
– Water (H2O)
• No solid residues.
• Maximize pressure to perform mechanical work.
8182222()25()16()18()CHlOgCOgHOg+ +
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Theory and Reality
• Combustion equations are expressions of
ideal combustion where only CO2 and H2O
are products.
• In limited oxygen incomplete combustionoccurs:
– Carbon monoxide is also produced.
– (21 O2 compared with 25 O2 with complete
combustion).
8182222()21()8()8()18()CHlOgCOgCOgHOg+ + +
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Emissions and the
Environment
• Typical car engine results in about 5 %
CO.
• CO2 and CO are both greenhouse gases.
• CO is also a health hazard.
• Catalytic converters convert CO into CO2.
22()()()OgCOgCOg+
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What Makes a Good Fuel?
• In the combustion process:
– C-C and C-H bonds are broken.
– C-O and H-O bonds are made.
• The bonds that are made are stronger than those that
are broken – energy is released – exothermic reaction.
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Energy Released and Bond
Strength
• As C-C bond strength
increases, the energy
released decreases:
– Combustion of ethane
(C-C = 348 kJ/mol)
more exothermic than
combustion of
acetylene (C-C =839
kJ/mol.
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Bearing the Torch
• Energy is not the onlyfactor.
• Acetylene (ethyne) isused in oxy-acetylenewelding torches ratherthan ethane orethene.
• Acetylene torchesreach 3,300 C andcan be used underwater.
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Methane and the Bermuda
Triangle
• Methane is a product of
decomposing organic
matter (Natural gas).
• Under water it can build
up in large pockets which
are then released.
• The water density is
suddenly reduced and
any floating object (ships)
will sink.
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All Shapes and Sizes
• Hydrocarbons come in different sizes:
– number of C atoms.
• Different types:
– single, double or triple bonds.
• Systematic naming is required to
distinguish the thousands of possibilities.
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It’s All Greek (Roots) To Me
• The first part of the name says how many C atoms are in the longestchain in the molecule.
• The second part of the name describes the bonds:– Ane single
– Ene double
– Yne triple
• Straight chain hydrocarbon begins with n-
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The Straight Chain Alkanes
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Chains and Branches
• Hydrocarbons also come inbranched chains:
– Main chain (longest) in blue.
– Branches (shorter) in orange.
• Side chains get name from #of C atoms plus –yl
• Longest chain is namedaccording to table:
– In this example longest chainhas 9 C atoms – nonane.
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Methyl Meet ethyl – ethyl
methyl• Longest chain is nonane.
– Number the chain C atoms so that branches have lowest numbers.
• Branches are methyl and ethyl.
– Methyl at 3 and ethyl at 5.
• Order branches alphabetically:
5-ethyl-3-methylnonane
• NOTE: no spaces in name; hyphens used to separate numbers andletters.
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Do Try These At Home
• Identify the longestchain in each case.
• In example 3, thelongest chain is bentnot straight. In 1 and2, numbering is samein either direction.
• 4-ethylheptane 5-propylnonane 3-methylhexane
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Multiple Bonds
• Alkenes: hydrocarbons containing double bonds.
• Position of double bond determined by numbering along main chain:
– Complete name is propene (3 C atoms, double bond must begin at C-1)
– Complete name is 3-octene (8 C atoms, double bond begins as C-3)
• Molecule contains triple bond and methyl group. Correct name is 4-methyl-1-pentyne.
– Multiple bonds must get lowest number possible (incorrect is 2-methyl-4-pentyne).
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Rings and Things
• Ring is regarded as the main group and the chain is a
separate entity:
– Begin numbering at position of double bond.
– Choose direction to make the side chain the lower number.
– Add cyclo to indicate ring.
– 3-butylcyclohexene
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What’s In a Name
• Given the name 2,2,4-trimethylpentane, drawthe molecule’s structure.
• What we know:– There is only one possible
structure.
– The longest chain has 5 Catoms (pent).
– All the bonds are single (-ane).
– There are three methylbranches (Tri and methyl).
– They are joined at C-2, C-2and C-4.
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Naming Multiple Groups
• When the same branch appears in the moleculemore than once, it is identified by a prefix.
• The naming scheme used for hydrocarbons isthe basis for naming all other organiccompounds.
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Structural Isomers
• For organic compounds,
the molecular formula is
not sufficient to specify a
unique molecule:
– C8H18 has several possible
isomers: same number of
atoms, but different
arrangement.
– Each isomer has a unique
name and structure but the
same molecular formula.
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Geometric Isomers
• Single bonds allow free rotation about the bond axis.
• Double bonds are rigid and don’t allow rotation.
• Different isomers arise by virtue of geometry:– Chain continuation on opposite sides: trans-– Chain continuation on same side: cis-
• Physical properties are quite different.
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I Hear You Knocking
• For efficient
operation, combustion
must occur at the
right moment to drive
the piston up and
move the crankshaft.
• Premature
combustion is
inefficient and results
in “knocking.”
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Checking the Ratings
• Molecular structureaffects combustion.
• Octane number describescombustion efficiency.
• Straight chain is worsethan branched:– 2,2,4-trimethylpentane has
octane rating 100.
– n-heptane has rating 0.
• Gasoline is a complexmixture of differenthydrocarbons andadditives with octaneratings from 85 – 97.
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A Hot Cocktail
• The Molotov Cocktail was a homemade
bomb consisting of liquid hydrocarbons
inside a bottle.
• Intermolecular forces determine whether a
substance is a gas, a liquid, or a solid.
• Hydrocarbons are nonpolar and have only
weak interactions between the molecules:
– making for low boiling point.
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Boiling Point and Molar
Mass• Molecular interactions
increase withmolecule size:– Methane – n-butane
are gases (1 – 4 Catoms).
– n-pentane – n-heptadecane areliquids (5 – 17 Catoms).
– n-octadecane is solid( 17 C atoms).
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Hydrocarbons and Daily Life
• Hydrocarbons appear
in many familiar
products:
– Fuels – natural gas,
propone, butane.
– Lubricants and oils.
– Fabrics.
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Fractional Distillation
• Crude oil is a fossil fuel –organic matter
decomposed over time.
• Complex mixture of
different sized
hydrocarbons.
• Refinement is achieved
by distillation.
• Lighter fractionscondense higher up the
fractionating column.
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The Ether
• Molecules beside hydrocarbons function asfuels.
• Ether contains two hydrocarbon groupsseparated by an O atom.
• General formula is: R-O-R'
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Naming Ethers
• When the hydrocarbon groups are
different, the name orders the two group
alphabetically and ends in ether.
– Butyl methyl ether: H3CCH2CH2CH2-O-CH3
• When the groups are the same the prefix
di- is used.
– Dimethyl ether: H3C-O-CH3
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Ether and Alcohol: Isomers
• Diethyl ether was the first important
anesthetic.
• Diethyl ether and n-butanol are isomers –
molecular formula C4H10O.
• Physical and chemical properties are quite
different.
– Diethyl ether b.p. = 35ºC, insoluble in water
– n-butanol b.p. = 118ºC, soluble in water
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Hydrogen Bonding and Boiling
Point• A hydrogen bond requires
an H atom attached to anelectronegative atom O,N or F.– Atom attached to H is the
hydrogen bond donor.– Atom accepting the H is the
hydrogen bond acceptor.
• The position of the Oatom controls properties.– In n-butanol the polar O-H
bond allows H-bonding.
– In diethyl ether the O atomis between two C atoms –no H-bonding.
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Anesthetics and Fuels
• Volatility of diethyl ether makes it a good
anesthetic – although flammability is
undesirable.
• Alcohols also undergo combustion.
• Ethanol is an important fuel additive to
reduce CO emissions.
3223222212810HCCHOCHCHOCOHO + +
3222222212810HCCHCHCHOHOCOHO+ +
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Cleaning Up Our Act
• The Clean Air Act of 1991 introduced newstandards to reduce hazardous exhaustemissions – maximize conversion of CO toCO2.
• Oxygenates: Adding O to the fuel beforecombustion rather than afterwards.
• Two options:– Ethanol – expensive to produce
– Methyl tert-butyl ether (MTBE)
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Unwanted Consequences of
MTBE• Ethers are more polar
than hydrocarbons anddissolve slightly in water.
• Gasoline containingMTBE posesenvironmental hazard:– MTBE is carcinogenic.
– MTBE does not degrade.
• MTBE contamination ofwater supplies is a majorhealth issue.
• Ethanol poses a safer,but a more expensivealternative.
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A Bigger Bang
• Fuel plus oxygen = bang.
• Nitroglycerin (1867)
revolutionized explosive
technology.
• Alfred Nobel received
more than 400 patents
related to explosives.
• The Nobel prizes are his
legacy.
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Nitroglycerin: The All-In-One
Explosive
• Nitroglycerin does not require additional
oxygen to detonate – they are supplied
from within.
– 4 molecules of liquid produce 29 molecules of
gas.
– Reaction is highly exothermic.
• Perfect combination for blasting power.
353922224()6()12()10()()CHNOlNgCOgHOgOgenergy+ + + +
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Exo- or Endo-
• Heat change in reactionis determined by bondenergies.– Molecule with weak bonds
is more likely to react.
– Stronger bonds in productsthan reactants will producemore energy in reaction.
• Bonds in product arestronger than bonds innitroglycerin – reaction ishighly exothermic.
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Energy Bookkeeping
• Doing the sums on the bonds being broken:
• Doing the sums on the bonds being made:
• 7420 kJ are liberated in the reaction.
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Summary of Exothermic and
Endothermic Reactions
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Nitrogen and Explosives
• Two factors make N an important component ofexplosives:– N-O bonds are weak.
– N≡N bonds are very strong.
• A new explosive molecule based on picric acid appearedin the 19th century.
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TNT: User-Friendly Explosive
• Picric acid was too
unpredictable to be a
useful explosive.
• Enter TNT:
7536222()3()12()5()2()CHNOsNgCOgHgCsenergy+ + + +
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Primers for TNT
• TNT is much more
stable than picric acid
and requires a primer
like 1,3-
Dinitrobenzene.
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High and Low Explosives
• Low explosives (like hydrocarbons):
– Must be confined in small volume.
– Require initial mixing with oxygen.
• High explosive:
– Produce energy immediately.
– Rate of reaction is rapid and goes to
completion.
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What Makes Reactions
Happen?• Endothermic reactions happen spontaneously.
• Some exothermic reactions don’t occur.
• Disorder (Entropy) determines if reactions happen:Second law of thermodynamics states that entropy of theuniverse is always increasing.
• Things tend to go from order to disorder.
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Does Vacuuming the Carpet
Violate Physical Law?
• Vacuuming restores order to a room. Is this a
violation of the second law?
– Electrical power drives the vacuum cleaner.
– Steam drives the turbine that produces the electrical
power.
– Production of steam results in large entropy increase.
• Need to consider the entire universe: entropy
may decrease in the room, but has increased in
the universe elsewhere.
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How is A Person Like A Car
• Respiration obtains
energy from glucose.
• A combustion
reaction occurring in
the body.
6126222 ()6()6()6()CHOsOgCOgHOgenergy+ + +
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Entropy and Explosions
• Combustion reactions and explosions are very
high entropy processes:
– Reactants are liquids or solids.
– Products are large numbers of gas molecules.
• Heat and entropy can be opposing influences:
– Endothermic reactions can proceed provided the
entropy increase is sufficient.
– Exothermic reactions can be prevented if there is an
entropy decrease.
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Complex Analysis
• Fuels are complex mixtures of different
hydrocarbons.
• Analysis of the vapor left after a fire is
sufficiently sensitive to identify the
composition of the mixture.
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Gas Chromatography
• Chromatography
separates a mixture of
substances according to
their different attraction to
a stationary phase and a
moving phase:
– Molecules that prefer the
column move slowly.
– Molecules that prefer the
moving phase travel
quickly.
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Chromatograms
• If the column is long
enough the mixture
becomes separated
into pure
components.
• Substances can be
identified by
comparison with
known substances.
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Fingerprint File
• Gasoline is a complex
mixture:
– Small molecules appear
first (prefer mobile phase).
– Large molecules appear
later (prefer stationary
phase).
• The chromatogram for
each sample will be
unique and is a fingerprint
that can be used to detect
it elsewhere.
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Gas Chromatography and
Airport Security
• Gas chromatography
can be used to detect
trace amounts of
volatile explosives.
• Samples can be
taken at airport
security and analyzed
for the presence or
absence of TNT.