Lecture 4 - Alkanes and Cycloalkanes smart board
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Transcript of Lecture 4 - Alkanes and Cycloalkanes smart board
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General
Organic ChemistryTwo credits
Second Semester 2009
King Saud bin Abdulaziz University for Health Science
Reference Book: Organic Chemistry: A Brief Course, by Robert C. Atkins and Francis A. CareyThird Edition
Instructor: Rabih O. Al-Kaysi, PhD.
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Chapter 2Chapter 2
Alkanes and Cycloalkanes
Lecture 3
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IUPAC Nomenclature ofIUPAC Nomenclature of
Unbranched Alkanes Unbranched Alkanes
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Retained:Retained:
methanemethane CHCH44
ethaneethane CHCH33CHCH33
propanepropane CHCH33CHCH22CHCH33
butanebutaneCHCH33CHCH22CHCH22CHCH33
IUPAC Names of Unbranched AlkanesIUPAC Names of Unbranched Alkanes
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Note:Note:nn-prefix is not part of IUPAC name of-prefix is not part of IUPAC name ofany alkane.any alkane.
For example: For example: nn-butane is "common name" -butane is "common name" for CHfor CH33CHCH22CHCH22CHCH33;; butane is "IUPAC name."butane is "IUPAC name."
Others:Others:
Latin or Greek prefix for number of Latin or Greek prefix for number of
carbons + ane suffixcarbons + ane suffix
IUPAC Names of Unbranched AlkanesIUPAC Names of Unbranched Alkanes
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Number of carbons Number of carbons NameName StructureStructure
55 pentanepentane CHCH33(CH(CH22))33CHCH33
66 hexanehexane CHCH33(CH(CH22))44CHCH33
77 heptaneheptane CHCH33(CH(CH22))55CHCH33
88 octaneoctane CHCH33(CH(CH22))66CHCH33
99 nonanenonane CHCH33(CH(CH22))77CHCH33
1010 decanedecane CHCH33(CH(CH22))88CHCH33
IUPAC Names of Unbranched AlkanesIUPAC Names of Unbranched Alkanes
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Number of carbons Number of carbons NameName StructureStructure
1111 undecaneundecane CHCH33(CH(CH22))99CHCH33
1212 dodecanedodecane CHCH33(CH(CH22))1010CHCH33
1313 tridecanetridecane CHCH33(CH(CH22))1111CHCH33
1414 tetradecanetetradecane CHCH33(CH(CH22))1212CHCH33
1515 pentadecanepentadecane CHCH33(CH(CH22))77CHCH33
1616 hexadecanehexadecane CHCH33(CH(CH22))88CHCH33
IUPAC Names of Unbranched AlkanesIUPAC Names of Unbranched Alkanes
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Applying the IUPAC Rules:Applying the IUPAC Rules:The Names of the CThe Names of the C66HH1414 Isomers Isomers
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CHCH33CHCH22CHCH22CHCH22CHCH22CHCH33
(CH(CH33))22CHCHCHCH22CHCH22CHCH33
(CH(CH33CHCH22))22CHCHCHCH33
(CH(CH33))22CHCH(CHCHCH(CH33))22
(CH(CH33))33CCHCCH22CHCH33
The CThe C66HH1414 Isomers Isomers
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CHCH33CHCH22CHCH22CHCH22CHCH22CHCH33
The IUPAC name of the unbranched alkaneThe IUPAC name of the unbranched alkanewith a chain of 6 carbons is hexane.with a chain of 6 carbons is hexane.
HexaneHexane
The CThe C66HH1414 Isomers Isomers
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Step 1) Step 1) Find the longest continuous carbonFind the longest continuous carbonchain and use the IUPAC name of thechain and use the IUPAC name of theunbranched alkane as the basis.unbranched alkane as the basis.
Step 2) Step 2) Add name of substituent as a prefix.Add name of substituent as a prefix.
Step 3) Step 3) Number the chain from the end nearestNumber the chain from the end nearestthe substituent, and identify the carbon to the substituent, and identify the carbon to which the substituent is attached by number.which the substituent is attached by number.
IUPAC Nomenclature of Branched IUPAC Nomenclature of Branched AlkanesAlkanes
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(CH(CH33))22CHCHCHCH22CHCH22CHCH33
(CH(CH33CHCH22))22CHCHCHCH33
2-Methylpentane2-Methylpentane
3-Methylpentane3-Methylpentane
The CThe C66HH1414 Isomers Isomers
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(CH(CH33))22CHCH(CHCHCH(CH33))22
(CH(CH33))33CCHCCH22CHCH33
2,3-Dimethylbutane2,3-Dimethylbutane
2,2-Dimethylbutane2,2-Dimethylbutane
Use replicating prefixes (di-, tri-, tetra-, etc.) Use replicating prefixes (di-, tri-, tetra-, etc.) according to the number of identical substituentsaccording to the number of identical substituentsattached to the main chain.attached to the main chain.
The CThe C66HH1414 Isomers Isomers
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Alkyl GroupsAlkyl Groups
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Methyl and Ethyl GroupsMethyl and Ethyl Groups
MethylMethyl
EthylEthyl CC CCHH
HH HH
HH HH
CHCH33CHCH22
CCHH
HH
HH
CHCH33oror
oror
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Unbranched Alkyl GroupsUnbranched Alkyl Groups
If potential point of attachment is at the endIf potential point of attachment is at the endof the chain, take the IUPAC name of theof the chain, take the IUPAC name of thecorresponding unbranched alkane and replacecorresponding unbranched alkane and replacethe -the -aneane ending by - ending by -ylyl..
RRHHRR
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ButylButyl
If potential point of attachment is at the endIf potential point of attachment is at the endof the chain, take the IUPAC name of theof the chain, take the IUPAC name of thecorresponding unbranched alkane and replacecorresponding unbranched alkane and replacethe -the -aneane ending by - ending by -ylyl..
RRHHRR
CHCH33CHCH22CHCH22CHCH22CC CCHH
HH HH
HH HH
CC CC
HH HH
HH HH
oror
Unbranched Alkyl GroupsUnbranched Alkyl Groups
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HexylHexylCHCH33(CH(CH22))44CHCH22
CHCH33(CH(CH22))55CHCH22
CHCH33(CH(CH22))1616CHCH22
HeptylHeptyl
OctadecylOctadecyl
Unbranched Alkyl GroupsUnbranched Alkyl Groups
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The CThe C33HH77 Alkyl Groups Alkyl Groups
CHCH33CHCH22CHCH22CC CCHH
HH HH
HH HH
CC
HH
HH
oror
andand
CHCH33CHCHCHCH33CC CCHH
HH HH
HH
HHCC
HH
HH
oror
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CHCH33CHCH22CHCH22CC CCHH
HH HH
HH HH
CC
HH
HH
oror
IUPAC name: PropylIUPAC name: Propyl
Common name: Common name: nn-Propyl-Propyl
The CThe C33HH77 Alkyl Groups Alkyl Groups
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Naming Alkyl GroupsNaming Alkyl Groups
Step 1:Step 1: Identify longest continuous chain starting at Identify longest continuous chain starting at point of attachment.point of attachment.
Step 2: Step 2: Drop -Drop -aneane ending from name of unbranched ending from name of unbranched alkane having same number of carbons as alkane having same number of carbons as longest continuous chain and replace by -longest continuous chain and replace by -ylyl..
Step 3:Step 3: Identify substituents on longest continuous Identify substituents on longest continuous chain.chain.
Step 4:Step 4: Chain is always numbered starting atChain is always numbered starting atpoint of attachment.point of attachment.
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IUPAC name: 1-MethylethylIUPAC name: 1-Methylethyl
Common name: IsopropylCommon name: Isopropyl
CHCH33CHCHCHCH33CC CCHH
HH HH
HH
CC
HH
HH
ororHH
The CThe C33HH77 Alkyl Groups Alkyl Groups
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CHCH33CHCH22CHCH22CC CCHH
HH HH
HH HH
CC
HH
HH
oror
Classification: Primary alkyl groupClassification: Primary alkyl group
Alkyl groups are classified according to theAlkyl groups are classified according to thedegree of substitution at the carbon that bears thedegree of substitution at the carbon that bears thepoint of attachment. A carbon that is directlypoint of attachment. A carbon that is directlyattached to one other carbon is a primary carbon.attached to one other carbon is a primary carbon.
The CThe C33HH77 Alkyl Groups Alkyl Groups
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Classification: Secondary alkyl groupClassification: Secondary alkyl group
Alkyl groups are classified according to theAlkyl groups are classified according to thedegree of substitution at the carbon that bears thedegree of substitution at the carbon that bears thepoint of attachment. A carbon that is directlypoint of attachment. A carbon that is directlyattached to two other carbons is a secondary carbon.attached to two other carbons is a secondary carbon.
CHCH33CHCHCHCH33CC CCHH
HH HH
HH
CC
HH
HH
ororHH
The CThe C33HH77 Alkyl Groups Alkyl Groups
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IUPAC name: 2-MethylpropylIUPAC name: 2-Methylpropyl
Common name: IsobutylCommon name: Isobutyl
Classification: Primary alkyl groupClassification: Primary alkyl group
112233CC
HH
CHCH22
CHCH33
CHCH33
The CThe C44HH99 Alkyl Groups Alkyl Groups
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IUPAC name: 1,1-DimethylethylIUPAC name: 1,1-Dimethylethyl
Common name: Common name: terttert-Butyl-Butyl
Classification: Tertiary alkyl groupClassification: Tertiary alkyl group
11 22CC CHCH33
CHCH33
CHCH33
The CThe C44HH99 Alkyl Groups Alkyl Groups
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IUPAC Names of HighlyIUPAC Names of Highly
Branched AlkanesBranched Alkanes
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Branched alkanesBranched alkanes OctaneOctane
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4-Ethyloctane4-Ethyloctane
Branched alkanesBranched alkanes
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4-Ethyl-3-methyloctane4-Ethyl-3-methyloctane
List substituents in alphabetical order.List substituents in alphabetical order.
Branched alkanesBranched alkanes
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4-Ethyl-3,5-dimethyloctane4-Ethyl-3,5-dimethyloctane
List substituents in alphabetical order.List substituents in alphabetical order.But don't alphabetize di-, tri-, tetra-, etc.But don't alphabetize di-, tri-, tetra-, etc.
Branched alkanesBranched alkanes
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First Point of Difference RuleFirst Point of Difference Rule
The chain is numbered in the direction that The chain is numbered in the direction that gives the lower locant to the substituent at the gives the lower locant to the substituent at the first point of difference in the names.first point of difference in the names.
Don't add locants!Don't add locants!
2,2,6,6,7-Pentamethyloctane?2,2,6,6,7-Pentamethyloctane?
2,3,3,7,7-Pentamethyloctane?2,3,3,7,7-Pentamethyloctane?
What is correct name?What is correct name?
1122 33
4455
6677
88
88
77 6655
4433
2211
Just for general knowledge, will not be tested on
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First Point of Difference RuleFirst Point of Difference Rule
The chain is numbered in the direction that The chain is numbered in the direction that gives the lower locant to the substituent at the gives the lower locant to the substituent at the first point of difference in the names.first point of difference in the names.
Don't add locants!Don't add locants!
2,2,6,6,7-Pentamethyloctane?2,2,6,6,7-Pentamethyloctane?
What is correct name?What is correct name?
88
77 6655
4433
2211
Just
for
gen
eral
kn
owle
dge
, wil
l not
be
test
ed o
n
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CCnnHH22nn
Cycloalkane NomenclatureCycloalkane Nomenclature
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CycloalkanesCycloalkanes
Cycloalkanes are alkanes that contain a ring of Cycloalkanes are alkanes that contain a ring of three or more carbons.three or more carbons.
Count the number of carbons in the ring, and Count the number of carbons in the ring, and add the prefix add the prefix cyclocyclo to the IUPAC name of the to the IUPAC name of the unbranched alkane that has that number of unbranched alkane that has that number of carbons.carbons.
CyclopentaneCyclopentane CyclohexaneCyclohexane
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EthylcyclopentaneEthylcyclopentane
CycloalkanesCycloalkanes
CHCH22CHCH33
Name any alkyl groups on the ring in the usual Name any alkyl groups on the ring in the usual way.way.
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Name any alkyl groups on the ring in the usual Name any alkyl groups on the ring in the usual way.way.
List substituents in alphabetical order and countList substituents in alphabetical order and countin the direction that gives the lowest numericalin the direction that gives the lowest numericallocant at the first point of difference.locant at the first point of difference.
3-Ethyl-1,1-dimethylcyclohexane3-Ethyl-1,1-dimethylcyclohexane
CHCH22CHCH33
HH33CC CHCH33
CycloalkanesCycloalkanes
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Sources of Alkanes and CycloalkanesSources of Alkanes and Cycloalkanes
Just for general knowledge, will not be tested on
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Crude oilCrude oil
Just for general knowledge, will not be tested on
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Crude oilCrude oil
Refinery gasRefinery gasRefinery gasRefinery gas
CC11-C-C44
Light gasolineLight gasoline(bp: 25-95 °C)(bp: 25-95 °C)
Light gasolineLight gasoline(bp: 25-95 °C)(bp: 25-95 °C)
CC55-C-C1212
NaphthaNaphtha(bp 95-150 °C)(bp 95-150 °C)
NaphthaNaphtha(bp 95-150 °C)(bp 95-150 °C)
KeroseneKerosene(bp: 150-230 °C)(bp: 150-230 °C)
KeroseneKerosene(bp: 150-230 °C)(bp: 150-230 °C)
CC1212-C-C1515
Gas oilGas oil(bp: 230-340 °C)(bp: 230-340 °C)
Gas oilGas oil(bp: 230-340 °C)(bp: 230-340 °C)
CC1515-C-C2525
ResidueResidueResidueResidue
Just for general knowledge, will not be tested on
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CrackingCrackingconverts high molecular weight hydrocarbons converts high molecular weight hydrocarbons to more useful, low molecular weight onesto more useful, low molecular weight ones
ReformingReformingincreases branching of hydrocarbon chainsincreases branching of hydrocarbon chainsbranched hydrocarbons have better burningbranched hydrocarbons have better burningcharacteristics for automobile enginescharacteristics for automobile engines
Petroleum RefiningPetroleum Refining
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Physical Properties of AlkanesPhysical Properties of Alkanes
and Cycloalkanesand Cycloalkanes
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Boiling Points of Alkanes Boiling Points of Alkanes
governed by strength of intermolecular governed by strength of intermolecular attractive forcesattractive forces
alkanes are nonpolar, so dipole-dipole and alkanes are nonpolar, so dipole-dipole and dipole-induced dipole forces are absentdipole-induced dipole forces are absent
only forces of intermolecular attraction are only forces of intermolecular attraction are induced dipole-induced dipole forcesinduced dipole-induced dipole forces
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Induced dipole-Induced dipole attractive forcesInduced dipole-Induced dipole attractive forces
++––++
––
two nonpolar moleculestwo nonpolar molecules
center of positive charge and center of negative center of positive charge and center of negative charge coincide in eachcharge coincide in each
Just for general knowledge, will not be tested on
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++––++
––
movement of electrons creates an movement of electrons creates an instantaneous dipole in one molecule (left)instantaneous dipole in one molecule (left)
Induced dipole-Induced dipole attractive forcesInduced dipole-Induced dipole attractive forces
Just for general knowledge, will not be tested on
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++––++––
temporary dipole in one molecule (left) induces temporary dipole in one molecule (left) induces a complementary dipole in other molecule a complementary dipole in other molecule (right)(right)
Induced dipole-Induced dipole attractive forcesInduced dipole-Induced dipole attractive forces
Just for general knowledge, will not be tested on
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++––++ ––
temporary dipole in one molecule (left) induces temporary dipole in one molecule (left) induces a complementary dipole in other molecule a complementary dipole in other molecule (right)(right)
Induced dipole-Induced dipole attractive forcesInduced dipole-Induced dipole attractive forces
Just for general knowledge, will not be tested on
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++––++ ––
the result is a small attractive force between the result is a small attractive force between the two moleculesthe two molecules
Induced dipole-Induced dipole attractive forcesInduced dipole-Induced dipole attractive forces
Just for general knowledge, will not be tested on
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++–– ++ ––
the result is a small attractive force between the result is a small attractive force between the two moleculesthe two molecules
Induced dipole-Induced dipole attractive forcesInduced dipole-Induced dipole attractive forces
Just for general knowledge, will not be tested on
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increase with increasing number of carbonsincrease with increasing number of carbons
more atoms, more electrons, more more atoms, more electrons, more opportunities for induced dipole-inducedopportunities for induced dipole-induceddipole forces dipole forces
decrease with chain branchingdecrease with chain branching
branched molecules are more compact withbranched molecules are more compact withsmaller surface area—fewer points of contactsmaller surface area—fewer points of contactwith other molecules with other molecules
Boiling PointsBoiling Points
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increase with increasing number of carbonsincrease with increasing number of carbons
more atoms, more electrons, more more atoms, more electrons, more opportunities for induced dipole-inducedopportunities for induced dipole-induceddipole forces dipole forces
HeptaneHeptanebp 98°Cbp 98°C
OctaneOctanebp 125°Cbp 125°C
NonaneNonanebp 150°Cbp 150°C
Boiling PointsBoiling Points
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decrease with chain branchingdecrease with chain branching
branched molecules are more compact withbranched molecules are more compact withsmaller surface area—fewer points of contactsmaller surface area—fewer points of contactwith other molecules with other molecules
Octane: bp 125°COctane: bp 125°C 2-Methylheptane: bp 118°C2-Methylheptane: bp 118°C
2,2,3,3-Tetramethylbutane: bp 107°C2,2,3,3-Tetramethylbutane: bp 107°C
Boiling PointsBoiling Points
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All alkanes burn in air to giveAll alkanes burn in air to givecarbon dioxide and water.carbon dioxide and water.
Chemical Properties:Chemical Properties:
Combustion of AlkanesCombustion of Alkanes
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increase with increasing number of carbonsincrease with increasing number of carbons
more moles of Omore moles of O22 consumed, more moles consumed, more molesof COof CO22 and H and H22O formedO formed
Heats of CombustionHeats of Combustion
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4817 kJ/mol4817 kJ/mol
5471 kJ/mol5471 kJ/mol
6125 kJ/mol6125 kJ/mol
654 kJ/mol654 kJ/mol
654 kJ/mol654 kJ/mol
HeptaneHeptane
OctaneOctane
NonaneNonane
Heats of CombustionHeats of Combustion
Just for general knowledge, will not be tested on
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increase with increasing number of carbonsincrease with increasing number of carbons
more moles of Omore moles of O22 consumed, more moles consumed, more molesof COof CO22 and H and H22O formedO formed
decrease with chain branchingdecrease with chain branching
branched molecules are more stablebranched molecules are more stable(have less potential energy) than their(have less potential energy) than theirunbranched isomersunbranched isomers
Heats of CombustionHeats of Combustion
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5471 kJ/mol5471 kJ/mol
5466 kJ/mol5466 kJ/mol
5458 kJ/mol5458 kJ/mol
5452 kJ/mol5452 kJ/mol
5 kJ/mol5 kJ/mol
8 kJ/mol8 kJ/mol
6 kJ/mol6 kJ/mol
Heats of CombustionHeats of Combustion
Just for general knowledge, will not be tested on
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Isomers can differ in respect to their stability.Isomers can differ in respect to their stability.
Equivalent statement:Equivalent statement:
Isomers differ in respect to their potential energy.Isomers differ in respect to their potential energy.
Differences in potential energy can be measured by Differences in potential energy can be measured by comparing heats of combustion.comparing heats of combustion.
Important PointImportant Point
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8CO8CO22 + 9H + 9H22OO
5452 kJ/mol5452 kJ/mol5458 kJ/mol5458 kJ/mol
5471 kJ/mol5471 kJ/mol
5466 kJ/mol5466 kJ/molOO22++ 2525
22
OO22++ 2525
22 OO22++ 2525
22 OO22++ 2525
22
Just for general knowledge, will not be tested on