Chapter 2:Chapter 2: Alkanes,Alkanes,
Thermodynamics, andThermodynamics, and
KineticsKinetics
2,2,4-Trimethylpentane:2,2,4...
CombustionCombustion
How warm,How warm,
how fast?how fast?
PetroleumPetroleum
!!!!
All Reactions AreAll Reactions Are
EquilibriaEquilibria
-23.4 kcal/mol-23.4 kcal/mol
““Barrier” kcal/molBarrier” kcal/mol ...
1.1. Chemical Thermodynamics:Chemical Thermodynamics:
Energy changes during reaction, extent ofEnergy changes during react...
[ ][ ] = concentration in mol L= concentration in mol L-1-1
Equilibria: Two typical casesEquilibria: Two typical cases
[[A...
Gibbs Free Energy, ∆Gibbs Free Energy, ∆ G°G°
∆∆G°G° = -= -RRTT lnlnKK = -2.3= -2.3 RRTT loglogKK
TT in kelvins, K (zero k...
At 25ºC (298°K):At 25ºC (298°K): ΔΔGºGº = - 1.36 log= - 1.36 logKK
Equilibria and FreeEquilibria and Free
EnergyEnergy
∆∆G°G° == ∆∆H°H° -- TT∆∆S°S° calcal-1-1
degdeg-1-1
molmol-1-1
oror entropy unitsentropy units,,
Kcal molKcal mol-1-1
Entha...
CCHH33CCHH22――HH ClCl――ClCl CCHH33CCHH22――ClCl ++ HH――ClCl
101101 10310384845858
∆∆H°H° negative: called “negative: called...
Boltzmann’s Tombstone (1844-Boltzmann’s Tombstone (1844-
1906)1906)
SS == kk x logx logWW
““ChaosChaos””
EntropyEntropy Bo...
Ice creamIce cream
makers:makers:
cool withcool with
ice/NaClice/NaCl;;
Dissolution ofDissolution of
salt issalt is
endoth...
RatesRates
All processes haveAll processes have “activation barriers”“activation barriers”..
Rate controlled by:Rate contr...
2.2. ConcentrationConcentration (the number of collisions(the number of collisions
increase with concentration)increase wi...
Boltzmann DistributionBoltzmann Distribution
TheThe average kinetic energyaverage kinetic energy of molecules at room temp...
Rate measurementsRate measurements : Give: Give Rate LawsRate Laws, tell us, tell us
something about TS structure. Most co...
If rate =If rate = kk [A][B][A][B]
22ndnd
orderorder
rate lawrate law
BimolecularBimolecular reaction (TS involves both A ...
Potential EnergyPotential Energy
DiagramsDiagrams
ReactantReactant
ProductProduct
[A][A]
[B][B]
∆∆HH °° (when(when ∆∆SS °°...
Many reactions have many steps, but there isMany reactions have many steps, but there is
always aalways a rate determining...
AA
BB
CC
Which is right: On heating,Which is right: On heating,
a.a. Compound A converts to C directly.Compound A converts...
AcidAcid--BaseBase EquilibriaEquilibria
AcidAcid Conjugate BaseConjugate Base
Brønsted and Lowry:Brønsted and Lowry:
Acid ...
OO
HH
HH
HH ClCl
HH
HH
OOHH ++ ClCl
AcidAcid--BaseBase: Electron: Electron
“Pushing” and“Pushing” and
ElectrostaticsElectr...
AcidityAcidity
constantconstant
mol/Lmol/LSolvent 55Solvent 55KK ==
[H[H33O] [O] [AA]]
[[HAHA] [H] [H22O]O]
KKaa == KK x 5...
AcidityAcidity
AcidityAcidity increases with:increases with:
1. Increasing size of A (H A gets weaker; charge1. Increasing...
StrongStrong
WeakWeak
VeryVery
weakweak
Relative Acid StrengthsRelative Acid Strengths
Lewis acids:Lewis acids: e-deficiente-deficient
Lewis bases:Lewis bases:
BBFF
FF
FF
Lone e-pairsLone e-pairs
6e6e
NN
RR
RR...
Lewis Acid-BaseLewis Acid-Base
ElectrostaticsElectrostatics
FF
FF
BB
FF
OO
CCHH22CCHH33
CCHH22CCHH33
BBFF
FF
FF
OO
CCHH22C...
HydrocarbonsHydrocarbons withoutwithout
Straight chain:Straight chain: CCHH33CCHH22CCHH22CCHH33
AlkanesAlkanes
Branched:Br...
SameSame molecular formulamolecular formula,, differentdifferent connectivityconnectivity
Cyclic:Cyclic:
Bicyclic:Bicyclic...
InsertInsert-CH-CH22-- groups intogroups into CC--
CC bonds.bonds.
Straight chainStraight chain
CCHH33((CCHH22))xxCCHH33
G...
Barry SharplessBarry Sharpless
(Scripps)(Scripps) NP 2001NP 2001
Dat
e
Mon Sep 12 23:56:24 EDT
2005
Cou
nt
 26,676,640 org...
Angew. Chem. Int. Ed. 2005, 44, 1504 –1508 (edited)
The development of modern medicine largely depends on the
continuous d...
The Names of Alkanes are BasedThe Names of Alkanes are Based
on theon the
IUPAC RulesIUPAC Rules
Change endingChange ending –ane–ane toto –yl–yl, as in, as in
methmethaneane / meth/ methylyl, hex, hexaneane / hex/ hexyl...
IUPAC RulesIUPAC Rules
1.1. Find theFind the longest chainlongest chain and name it (Table 2-5)and name it (Table 2-5)
CCH...
2. Name substituents (as alkyl or2. Name substituents (as alkyl or halohalo))
a.a. For straight chain R: Methyl, ethyl, pr...
Branched Alkyl GroupsBranched Alkyl Groups
c.c. Multiple same substituents:Multiple same substituents:
ForFor R = straightR = straight, use prefix di-, tri-, tetra-,...
dd.. Common names: we will use colloquiallyCommon names: we will use colloquially
isopropyl,isopropyl, terttert-butyl, neo...
33. Number stem, starting from the end. Number stem, starting from the end
closest to a substituent:closest to a substitue...
44.. NameName the alkane inthe alkane in alphabeticalalphabetical (not(not numericalnumerical))
order of substituents,orde...
Problem:Problem:
BrBr
ClCl
II
Longest chain?Longest chain?
33
55
88
66
44
77
22
11
BrBr
ClCl
II
Substituents?Substituents?
IodoIodo
1-Chloroethyl1-Chloroethyl
DimethylDimethyl
BromoBromo
33
55
88
66
44
77
22
11
BrBr
ClCl
II
Final name?Final name?
IodoIodo
1-Chloroethyl1-Chloroethyl
DimethylDimethyl
BromoBromo
33
55
88
66
44
77
22
11
BrBr
ClCl
II
1-Bromo-5-(1-chloroet...
Physical Properties of Alkanes:Physical Properties of Alkanes:
Intermolecular Forces Increase WithIntermolecular Forces In...
Coulomb forces in saltsCoulomb forces in salts Dipole-dipole interactionsDipole-dipole interactions
in polar moleculesin p...
London forces: Electron correlationLondon forces: Electron correlation
(Polarizability: Deformability of e-cloud)(Polariza...
The Rotamers of EthaneThe Rotamers of Ethane
StaggeredStaggered EclipsedEclipsed StaggeredStaggered
Newman ProjectionsNewman Projections
Note: Newman projection occurs along only one bond. Everything else isNote: Newman pr...
Rotation with NewmanRotation with Newman
ProjectionsProjections
Rotation Around Bonds is NotRotation Around Bonds is Not
“Free”: Barriers to Rotation“Free”: Barriers to Rotation
e-Repuls...
Potential EnergyPotential Energy
DiagramsDiagrams
(TS = transition state)(TS = transition state)
WalbaWalbaDStrDStr
Propane: Methyl IncreasesPropane: Methyl Increases
BarrierBarrier
Butane: Isomeric StaggeredButane: Isomeric Staggered
and Eclipsed Rotamersand Eclipsed Rotamers
Rotamers and EnergyRotamers and Energy
DiagramDiagram
WalbaWalbaDylanDylan
Chapter2烷烃
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Chapter2烷烃

  1. 1. Chapter 2:Chapter 2: Alkanes,Alkanes, Thermodynamics, andThermodynamics, and KineticsKinetics 2,2,4-Trimethylpentane:2,2,4-Trimethylpentane: AnAn octaneoctane
  2. 2. CombustionCombustion How warm,How warm, how fast?how fast? PetroleumPetroleum !!!!
  3. 3. All Reactions AreAll Reactions Are EquilibriaEquilibria -23.4 kcal/mol-23.4 kcal/mol ““Barrier” kcal/molBarrier” kcal/mol ExothermicityExothermicity CHCH33Cl + NaCl + Na++ -- OHOH CH3OH + Na+ Na++ ClCl-- CHCH44 + O+ O22 COCO22 + 2H+ 2H22OO What governs these equilibria?What governs these equilibria? ~20~20 highhigh -213 kcal/mol-213 kcal/mol Equilibrium lies very much to the right.Equilibrium lies very much to the right. oror
  4. 4. 1.1. Chemical Thermodynamics:Chemical Thermodynamics: Energy changes during reaction, extent ofEnergy changes during reaction, extent of “completion of equilibration,” “to the left/right,”“completion of equilibration,” “to the left/right,” “driving force.”“driving force.” 2. Chemical Kinetics2. Chemical Kinetics:: How fast is equilibrium established; rates ofHow fast is equilibrium established; rates of disappearance of starting materials or appearancedisappearance of starting materials or appearance of productsof products Chemical Thermodynamics andChemical Thermodynamics and KineticsKinetics The two principles may or may not go in tandemThe two principles may or may not go in tandem
  5. 5. [ ][ ] = concentration in mol L= concentration in mol L-1-1 Equilibria: Two typical casesEquilibria: Two typical cases [[AA]] [[reactantsreactants]] [[BB]] [[productsproducts]] KK = equilibrium constant= equilibrium constant AA BB KK == [[CC][][DD]] [[AA][][BB]] IfIf KK large: reaction “complete,” “to the right,” “downhill.”large: reaction “complete,” “to the right,” “downhill.” How do we quantify?How do we quantify? Gibbs free energy, ∆Gibbs free energy, ∆G°G° KK A +BA +B C + DC + D KK ==KK ==1.1. 2.2.
  6. 6. Gibbs Free Energy, ∆Gibbs Free Energy, ∆ G°G° ∆∆G°G° = -= -RRTT lnlnKK = -2.3= -2.3 RRTT loglogKK TT in kelvins, K (zero kelvin = -273 °C)in kelvins, K (zero kelvin = -273 °C) RR = gas constant ~ 2cal deg= gas constant ~ 2cal deg-1-1 molmol-1-1 LargeLarge KK : Large: Large negativenegative ∆∆G°G° : downhill: downhill
  7. 7. At 25ºC (298°K):At 25ºC (298°K): ΔΔGºGº = - 1.36 log= - 1.36 logKK Equilibria and FreeEquilibria and Free EnergyEnergy
  8. 8. ∆∆G°G° == ∆∆H°H° -- TT∆∆S°S° calcal-1-1 degdeg-1-1 molmol-1-1 oror entropy unitsentropy units,, Kcal molKcal mol-1-1 EnthalpyEnthalpy ∆∆H°H° == heatheat of the reaction;of the reaction; for us, mainly due to changes in bondfor us, mainly due to changes in bond strengths:strengths: ∆∆H°H° = (Sum of strength of bonds broken)= (Sum of strength of bonds broken) – (sum of strengths of bonds made)– (sum of strengths of bonds made) EnthalpyEnthalpy ∆∆H°H° and Entropyand Entropy ∆∆S°S° oror e.u.e.u.
  9. 9. CCHH33CCHH22――HH ClCl――ClCl CCHH33CCHH22――ClCl ++ HH――ClCl 101101 10310384845858 ∆∆H°H° negative: called “negative: called “exothermicexothermic”” if positive: called “if positive: called “endothermicendothermic”” ∆∆S°S° = change in the= change in the “order”“order” of theof the system. Nature strives for disorder.system. Nature strives for disorder. More disorder =More disorder = positivepositive ∆∆SS °° (makes(makes a negative contribution to ∆a negative contribution to ∆G°G° )) ∆∆H°H° = 159 – 187 = -28 kcalmol= 159 – 187 = -28 kcalmol-1-1 ++ Example:Example:
  10. 10. Boltzmann’s Tombstone (1844-Boltzmann’s Tombstone (1844- 1906)1906) SS == kk x logx logWW ““ChaosChaos”” EntropyEntropy Boltzmann’s constantBoltzmann’s constant Two balls in two tight boxes:Two balls in two tight boxes: A.A. Confined to one box:Confined to one box: 1 Way1 Way B.B. Open access to second box:Open access to second box: 6 Ways: 1-2, 1-3, 1-4, 2-3, 2-4, 3-46 Ways: 1-2, 1-3, 1-4, 2-3, 2-4, 3-4 (Microstates(Microstates or extent ofor extent of freedom)freedom)
  11. 11. Ice creamIce cream makers:makers: cool withcool with ice/NaClice/NaCl;; Dissolution ofDissolution of salt issalt is endothermicendothermic,, but driven bybut driven by entropyentropy ∆∆H°H° = -15.5 kcal mol= -15.5 kcal mol-1-1 If # of molecules unchanged,If # of molecules unchanged, ∆∆S°S° small,small, ∆∆H°H° controls ( wecontrols ( we can estimate value from bondcan estimate value from bond strength tables)strength tables) ∆∆S°S° = -31.3 e.u.= -31.3 e.u. CCHH22 CCHH22 ++ HHClCl CCHH33CCHH22ClCl 2 molecules2 molecules 1 molecule1 molecule Chemical example:Chemical example:
  12. 12. RatesRates All processes haveAll processes have “activation barriers”“activation barriers”.. Rate controlled by:Rate controlled by: 1.1. Barrier heightBarrier height (structure of transition(structure of transition state TS)state TS)
  13. 13. 2.2. ConcentrationConcentration (the number of collisions(the number of collisions increase with concentration)increase with concentration) 3.3. TT (increased T means faster moving(increased T means faster moving molecules; number of collisions increases)molecules; number of collisions increases) 4. “4. “ProbabilityProbability” factor (how likely is a” factor (how likely is a collision to lead to reaction; depends oncollision to lead to reaction; depends on sterics, electronics)sterics, electronics)
  14. 14. Boltzmann DistributionBoltzmann Distribution TheThe average kinetic energyaverage kinetic energy of molecules at room temperatureof molecules at room temperature isis ~ 0.6 kcal/mol~ 0.6 kcal/mol.. What supplies the energy to get over the barrier?What supplies the energy to get over the barrier?
  15. 15. Rate measurementsRate measurements : Give: Give Rate LawsRate Laws, tell us, tell us something about TS structure. Most common:something about TS structure. Most common: If rate =If rate = kk [A][A] UnimolecularUnimolecular reaction (TS involves only A)reaction (TS involves only A) AA BB1.1. Reaction RateReaction Rate 1st1st orderorder rate lawrate law
  16. 16. If rate =If rate = kk [A][B][A][B] 22ndnd orderorder rate lawrate law BimolecularBimolecular reaction (TS involves both A and B).reaction (TS involves both A and B). How do we measure barrier ?How do we measure barrier ? Energy of activationEnergy of activation from Arrhenius equation:from Arrhenius equation: kk == RTRT --EEaa AeAe 2. A + B C2. A + B C at high T, k = A, “maximum rate”
  17. 17. Potential EnergyPotential Energy DiagramsDiagrams ReactantReactant ProductProduct [A][A] [B][B] ∆∆HH °° (when(when ∆∆SS °° small)small)∆∆GG °° EEaa kkrr kkff Reaction coordinate =Reaction coordinate = progress of reactionprogress of reaction kk forwardforward kk reversereverse KK == [A][A] [B][B] == [TS][TS] EE ‡
  18. 18. Many reactions have many steps, but there isMany reactions have many steps, but there is always aalways a rate determiningrate determining TSTS (bottleneck).(bottleneck). TSTS Rate Determining TransitionRate Determining Transition StateState
  19. 19. AA BB CC Which is right: On heating,Which is right: On heating, a.a. Compound A converts to C directly.Compound A converts to C directly. b.b. It goes first to B and then to C.It goes first to B and then to C. c.c. It stays where it is.It stays where it is. Problem:Problem:
  20. 20. AcidAcid--BaseBase EquilibriaEquilibria AcidAcid Conjugate BaseConjugate Base Brønsted and Lowry:Brønsted and Lowry: Acid = proton donorAcid = proton donor Base = proton acceptorBase = proton acceptor HHA + HA + H22OO HH33O +O + AA++ --
  21. 21. OO HH HH HH ClCl HH HH OOHH ++ ClCl AcidAcid--BaseBase: Electron: Electron “Pushing” and“Pushing” and ElectrostaticsElectrostatics ++ -- ++ ++ ++ +1+1 -1-1 AA BB Charge moves:Charge moves: e-pushinge-pushing arrowsarrows
  22. 22. AcidityAcidity constantconstant mol/Lmol/LSolvent 55Solvent 55KK == [H[H33O] [O] [AA]] [[HAHA] [H] [H22O]O] KKaa == KK x 55 =x 55 = [H[H33O][O][AA]] [[HAHA]] ++ ++ -- -- ppKKaa = -log= -log KKaa HHA + HA + H22OO HH33O +O + AA ++ --
  23. 23. AcidityAcidity AcidityAcidity increases with:increases with: 1. Increasing size of A (H A gets weaker; charge1. Increasing size of A (H A gets weaker; charge is better stabilized in larger orbital; down the PT)is better stabilized in larger orbital; down the PT) 3. Resonance, e.g.,3. Resonance, e.g., 2. Electronegativity (moving to the right in PT)2. Electronegativity (moving to the right in PT) CCHH33OOHH 15.515.5 CCHH33OO -- :::: :: :::: CCHH33CCOOHH OO :::: :::: 4.34.3 CCHH33 OO :::: :::: OOCC ::-- ppKKaa OOHH OO :::: :::: OO SS::-- OO:::: :::: HH22SOSO44 -5.0-5.0
  24. 24. StrongStrong WeakWeak VeryVery weakweak Relative Acid StrengthsRelative Acid Strengths
  25. 25. Lewis acids:Lewis acids: e-deficiente-deficient Lewis bases:Lewis bases: BBFF FF FF Lone e-pairsLone e-pairs 6e6e NN RR RR RR e-pushinge-pushing arrowsarrows BB FF FF FF RR RR OO OO RR RR BFBF33 ++ -- R―R―SSR―R―OO―R―R LewisLewis AcidsAcids andand BasesBases --
  26. 26. Lewis Acid-BaseLewis Acid-Base ElectrostaticsElectrostatics FF FF BB FF OO CCHH22CCHH33 CCHH22CCHH33 BBFF FF FF OO CCHH22CCHH33 CCHH22CCHH33 ++-- ++ ++
  27. 27. HydrocarbonsHydrocarbons withoutwithout Straight chain:Straight chain: CCHH33CCHH22CCHH22CCHH33 AlkanesAlkanes Branched:Branched: CCCCHH33 CCHH33 CCHH33 HH CC44HH1010 2-Methylpropane2-Methylpropane CC44HH1010 ButaneButane CCHH33 CCHH33 functional groupsfunctional groups Line notation:Line notation: 1 Å = 101 Å = 10-8-8 cmcm
  28. 28. SameSame molecular formulamolecular formula,, differentdifferent connectivityconnectivity Cyclic:Cyclic: Bicyclic:Bicyclic: Polycyclic . . . . . .Polycyclic . . . . . . CyclohexaneCyclohexane CC66HH1212 Bicyclo[2.2.0]octaneBicyclo[2.2.0]octane CC88HH1414 andand areare constitutional isomers.constitutional isomers.
  29. 29. InsertInsert-CH-CH22-- groups intogroups into CC-- CC bonds.bonds. Straight chainStraight chain CCHH33((CCHH22))xxCCHH33 General molecular formulaGeneral molecular formula for acyclic systems.for acyclic systems. Cyclic alkanes:Cyclic alkanes: CCnnHH22nn HomologousHomologous series:series:
  30. 30. Barry SharplessBarry Sharpless (Scripps)(Scripps) NP 2001NP 2001 Dat e Mon Sep 12 23:56:24 EDT 2005 Cou nt  26,676,640 organic and  inorganic substances    56,744,740 sequences
  31. 31. Angew. Chem. Int. Ed. 2005, 44, 1504 –1508 (edited) The development of modern medicine largely depends on the continuous discovery of new drug molecules for treating diseases. One striking feature of these drugs is their relatively small molecular weight (MW), which averages only 340. Recently, drug discovery has focused on even smaller building blocks with MW of 160 or less to be used as lead structures that can be optimized for biological activity by adding substituents. At that size it becomes legitimate to ask how many such very small molecules would be possible in total within the boundaries of synthetic organic chemistry? To address this question we have generated a database containing all possible organic structures with up to 11 main atoms under constraints defining chemical stability and synthetic feasibility. The database contains 13.9 million molecules with an average MW of 153, and opens an unprecedented window on the small-molecule chemical universe. Virtual Exploration of the Small-Molecule Chemical Universe below 160 Daltons Tobias Fink, Heinz Bruggesser, and Jean-Louis Reymond*
  32. 32. The Names of Alkanes are BasedThe Names of Alkanes are Based on theon the IUPAC RulesIUPAC Rules
  33. 33. Change endingChange ending –ane–ane toto –yl–yl, as in, as in methmethaneane / meth/ methylyl, hex, hexaneane / hex/ hexylyl Short notation: AlkaneShort notation: Alkane R-HR-H / alkyl/ alkyl R-R- ““Lingo”: RCLingo”: RCHH22 ““primaryprimary”” Naming AlkylNaming Alkyl SubstituentsSubstituents CC RR RR RR ““tertiarytertiary””CC HH RR RR ““secondarysecondary””
  34. 34. IUPAC RulesIUPAC Rules 1.1. Find theFind the longest chainlongest chain and name it (Table 2-5)and name it (Table 2-5) CCHH33CCHHCCHH22CCHH33 CCHH33 A (methyl substituted)A (methyl substituted) butanebutane AnAn octaneoctane (substituted by ethyl,(substituted by ethyl, two methyls)two methyls) When there are twoWhen there are two equal longestequal longest chains,chains, choose the one withchoose the one with more substituentsmore substituents 4 substituents4 substituents 3 substituents3 substituents
  35. 35. 2. Name substituents (as alkyl or2. Name substituents (as alkyl or halohalo)) a.a. For straight chain R: Methyl, ethyl, propylFor straight chain R: Methyl, ethyl, propyl etc.etc. b.b. For branched chain R:For branched chain R: αα. Find longest chain (starting from point of. Find longest chain (starting from point of attachment)attachment) ββ.. Name substituentsName substituents Example:Example: (Methylpropyl)(Methylpropyl) Halo: Bromo, fluoro, chloro, iodoHalo: Bromo, fluoro, chloro, iodo
  36. 36. Branched Alkyl GroupsBranched Alkyl Groups
  37. 37. c.c. Multiple same substituents:Multiple same substituents: ForFor R = straightR = straight, use prefix di-, tri-, tetra-,, use prefix di-, tri-, tetra-, penta-, etc.:penta-, etc.: DimethylDimethylhexanehexane ForFor R = branchedR = branched,, use: bis-, tris-, tetrakis-,use: bis-, tris-, tetrakis-, etc., and alkyl name in parentheses:etc., and alkyl name in parentheses: Bis(methylpropyl)Bis(methylpropyl)
  38. 38. dd.. Common names: we will use colloquiallyCommon names: we will use colloquially isopropyl,isopropyl, terttert-butyl, neopentyl-butyl, neopentyl
  39. 39. 33. Number stem, starting from the end. Number stem, starting from the end closest to a substituent:closest to a substituent: Branched substituents: Number from carbonBranched substituents: Number from carbon ofof attachmentattachment (C(C11)) 11 22 33 44 77 66 55 33 22 11 88 9944 11 22 33 Defined as 1Defined as 1 If both ends equidistant to the first substituent, proceedIf both ends equidistant to the first substituent, proceed until the first point of difference:until the first point of difference: 77 66 55 33 22 11 88 9944
  40. 40. 44.. NameName the alkane inthe alkane in alphabeticalalphabetical (not(not numericalnumerical)) order of substituents,order of substituents, locationlocation given by number prefix.given by number prefix. 66 11 33 44 55 2277 88 5-5-EEthyl-2-thyl-2-mmethyl-ethyl- octaneoctane 2-Methylbutane2-Methylbutane Alphabet:Alphabet: DDi-,i-, ttri-, etc.ri-, etc. not countednot counted for main stem R.for main stem R. ButBut:: CountedCounted when in branched Rwhen in branched R 66 44 11 33 55 2277 88 66 11 33 44 55 2277 88 5-5-EEthyl-2,2-di-thyl-2,2-di- mmethyloctaneethyloctane 5-(1,1-5-(1,1-DDimethylethyl)-imethylethyl)- 3-3-eethyloctanethyloctane NotNot countedcounted {{ CountedCounted
  41. 41. Problem:Problem: BrBr ClCl II Longest chain?Longest chain?
  42. 42. 33 55 88 66 44 77 22 11 BrBr ClCl II Substituents?Substituents?
  43. 43. IodoIodo 1-Chloroethyl1-Chloroethyl DimethylDimethyl BromoBromo 33 55 88 66 44 77 22 11 BrBr ClCl II Final name?Final name?
  44. 44. IodoIodo 1-Chloroethyl1-Chloroethyl DimethylDimethyl BromoBromo 33 55 88 66 44 77 22 11 BrBr ClCl II 1-Bromo-5-(1-chloroethyl)-7-iodo-2,2-dimethyloctane1-Bromo-5-(1-chloroethyl)-7-iodo-2,2-dimethyloctane
  45. 45. Physical Properties of Alkanes:Physical Properties of Alkanes: Intermolecular Forces Increase WithIntermolecular Forces Increase With SizeSize
  46. 46. Coulomb forces in saltsCoulomb forces in salts Dipole-dipole interactionsDipole-dipole interactions in polar moleculesin polar molecules Intermolecular ForcesIntermolecular Forces
  47. 47. London forces: Electron correlationLondon forces: Electron correlation (Polarizability: Deformability of e-cloud)(Polarizability: Deformability of e-cloud) IdealizedIdealized (pentane)(pentane) ExperimentalExperimental (heptane)(heptane) Intermolecular ForcesIntermolecular Forces
  48. 48. The Rotamers of EthaneThe Rotamers of Ethane StaggeredStaggered EclipsedEclipsed StaggeredStaggered
  49. 49. Newman ProjectionsNewman Projections Note: Newman projection occurs along only one bond. Everything else isNote: Newman projection occurs along only one bond. Everything else is a substituent.a substituent.
  50. 50. Rotation with NewmanRotation with Newman ProjectionsProjections
  51. 51. Rotation Around Bonds is NotRotation Around Bonds is Not “Free”: Barriers to Rotation“Free”: Barriers to Rotation e-Repulsione-Repulsion OrbitalOrbital stabilizationstabilization Transition stateTransition state isis eclipsedeclipsed MostMost stablestable rotamer isrotamer is staggeredstaggered Ethane has barrier to rotation of ~3 kcal molEthane has barrier to rotation of ~3 kcal mol-1-1 .. Barrier due to steric and electronic effects.Barrier due to steric and electronic effects. antibondingantibonding bondingbonding
  52. 52. Potential EnergyPotential Energy DiagramsDiagrams (TS = transition state)(TS = transition state) WalbaWalbaDStrDStr
  53. 53. Propane: Methyl IncreasesPropane: Methyl Increases BarrierBarrier
  54. 54. Butane: Isomeric StaggeredButane: Isomeric Staggered and Eclipsed Rotamersand Eclipsed Rotamers
  55. 55. Rotamers and EnergyRotamers and Energy DiagramDiagram WalbaWalbaDylanDylan

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