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CM1000, CM1002, CM2101 First file of lecture overheads for Organic Chemistry now available First Organic Chemistry lecture: Monday February 2 (Week 24) To access file: http://chemweb.ucc.ie Undergraduate 1st Year CM1000 Lecture Notes  [Scroll down to 'Dr. Humphrey Moynihan'] Lecture Package 1 Lecture Package 2 Lecture Package 3
[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Organic Chemistry 1 Part 1 of an introductory course in organic chemistry for CM1000, CM1002, CM2101 and related modules Dr. Humphrey A. Moynihan Kane Bldg 410 [email_address]
[object Object],[object Object],[object Object],[object Object],Ammonium cyanate (from mineral sources) ‘ Inorganic’ Urea (from urine) ‘ Organic’ W ö hler 1828 Ammonium cyanate Urea  (Heat) ,[object Object]
[object Object],[object Object],[object Object],[object Object],Lactic acid from milk (i.e. ‘organic’) 1.00 g 1.47 g  0.60 g  0.51 g Mol. Wt.  44  18  32 No. of Moles  0.033  0.033  0.016 1 C  2H  1O
[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
C-C  N-N  O-O Bond Dissociation Energy (kJ mol -1 ) 348  163  157 ,[object Object],[object Object],[object Object],[object Object],Linear molecules  Branched molecules  Cyclic molecules
[object Object],[object Object],Some properties of organic molecules ,[object Object],[object Object],[object Object]
Some organic chemicals DNA Essential oils ,[object Object],[object Object],[object Object],Materials Fuels Pigments
Organic chemicals make up ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Aspects of organic molecules ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Galactose:  a sugar obtained from milk Molecular weight = 180.156 g mol -1 Using elemental (combustion) analysis: a worked example What is the Molecular Formula? Carry out elemental analysis Galactose 0.1000 g Combustion CO 2 0.1450 g + H 2 O 0.0590 g + O 2 0.0540 g Mol. Wt. / g mol -1 44 18 32 No. of moles 0.0033 0.0033 0.0017 1C 2H 1O Empirical Formula = CH 2 O
Molecular Formula =  (CH 2 O) n Mol. Wt. “ CH 2 O ” = 30.026 g mol -1 Mol. Wt. galactose = 180.156 g mol -1      n = 6 i.e. Molecular Formula =  C 6 H 12 O 6 %C  =  6 x 12.011 180.156 x 100 Atomic Wts.  C: 12.011;  H: 1.008;  O: 15.999 =  40.00% Likewise: %H =  12 x 1.008 180.156 x 100 =  6.71% %O = 6 x 15.999 180.156 x 100 =  53.28%
Galactose C:  40.00% H:  6.71% O:  53.28% Elemental analysis data presented in this way Can use as an experimental measure of purity A pure material should return elemental analysis data which is within  ±0. 30% for each element E.g. given two samples of galactose Sample 1 C: 39.32% H:  7.18% O:  53.50% Sample impure Sample 2 C: 40.11% H:  6.70% O:  53.19% Sample pure
Electronic configuration of Carbon C  1s 2  2s 2   2p 2 ,[object Object],[object Object],[object Object],Ethane : a gas (b.p. ~ -100 o C) Empircal formula (elemental combustion analysis):   CH 3 i.e. an organic chemical Measure molecular weight (e.g. by mass spectrometry):  30.070 g mol -1 , i.e (CH 3 ) n   n = 2 Implies  molecular formula   =  C 2 H 6
Molecular formula : gives the identity and number of  different atoms comprising a molecule Ethane: molecular formula  =  C 2 H 6 Valency: Carbon  4 Hydrogen  1 Combining this information, can propose i.e. a  structural formula  for ethane
[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
[object Object],[object Object],[object Object],3 Dimensional shape of the molecule has  tetrahedral  carbons ,[object Object]
109.5  109.5  109.5  109.5  Need to be able to represent 3D molecular structure in 2D
e.g. = Or =
Angle between any two bonds at a Carbon atom = 109.5 o
Ethane: a gas b.p. ~ -100 o C Empirical formula:  CH 3 ,[object Object],[object Object],Molecular formula  C 2 H 6 ,[object Object],[object Object],[object Object]
[object Object],[object Object],[object Object],[object Object],[object Object]
Electronic configuration of Carbon  C  1s 2  2s 2  2p 2   Hydrogen  H  1s 1
[object Object],[object Object],[object Object],(2e - ) (1e - )  (1e - )   (1e - )  (1e - )
Bonding in ethane Atomic orbitals available: 2 Carbons, both contributing 4  sp 3  hybridised orbitals  6 Hydrogens, each contributing an  s  orbital Total atomic orbitals = 14 Combine to give 14 molecular orbitals 7 Bonding molecular orbitals; 7 anti-bonding molecular orbitals Electrons available to occupy molecular orbitals One for each  sp 3  orbital on Carbon; one for each  s  orbital on Hydrogen =  14 Just enough to fully occupy the bonding molecular orbitals Anti-bonding molecular orbitals not occupied
Ethane: molecular orbital diagram    molecular orbitals: symmetrical about the bond axis
Four  sp 3  hybridised orbitals can be arrayed to give tetrahedral geometry sp 3  hybridised orbitals from two Carbon atoms can overlap to form a Carbon-Carbon    bond C-C    bond Each  sp 3  orbital contributes one electron to form  C-C   [C .. C] Visualising the molecular orbitals in ethane
An s p 3  orbital extends mainly in one direction from the nucleus and forms bonds with other atoms in that direction.
Carbon  sp 3  orbitals can overlap with Hydrogen  1s  orbitals to form Carbon-Hydrogen    bonds    bonds: symmetrical about the bond axis [Anti-bonding orbitals also formed; not occupied by electrons] Each  sp 3  orbital contributes one electron; each  s  orbital contributes one electron to form  C-H [C .. H]
Geometry of Carbon in ethane is tetrahedral and is based upon  sp 3  hybridisation sp 3  hybridised Carbon = tetrahedral Carbon Tetrahedral angle    109.5 o
This represents a particular orientation of the  C-H  bonds on adjacent Carbons View along  C-C  bond: Newman projection Can select one C-H bond on either carbon and define a  dihedral angle  or  torsional angle ( φ ) φ
 
φ   = 60 o Staggered conformation Minimum energy conformation (least crowded possible conformation) C-C    bonds: symmetrical about the bond axes. In principle, no barrier to rotation about  C-C  bond Could have  φ   = 0 o Eclipsed conformation Maximum energy conformation (most crowded possible conformation) =
[object Object],[object Object],Steric hindrance exists between the eclipsing  C-H  bonds in this conformation ,[object Object],[object Object],[object Object]
Conformations: different orientations of molecules  arising from rotations about  C-C    bonds Consider one full rotation about the  C-C  bond in ethane Start at  φ  = 0   (eclipsed conformation) ,[object Object],Total: 12 kJ mol -1  torsional strain
φ  = 0  Rotate 60  Eclipsed conformation strain energy 12 kJ mol -1 φ  = 60  Staggered conformation strain energy 0 kJ mol -1 Rotate 60  φ  = 120  Eclipsed conformation strain energy 12 kJ mol -1
Rotate 60  φ  = 180  Staggered conformation strain energy 0 kJ mol -1 Rotate 60  φ  = 240  Eclipsed conformation strain energy 12 kJ mol -1 Rotate 60 
φ  = 300  Staggered conformation strain energy 0 kJ mol -1 Rotate 60  φ  = 360  Full rotation Return to starting position Eclipsed conformation strain energy 12 kJ mol -1 Identical to that at  φ  = 0  Hence, in one full rotation about the  C-C  bond ,[object Object],[object Object],[object Object]
Can plot torsional angle  φ  as a function of strain energy  12 kJ mol -1  = energy barrier to rotation about the C-C bond in ethane Too low to prevent free rotation at room temperature
Ethane C 2 H 6 ,[object Object],[object Object],[object Object],Do other molecules exist which have these properties? Yes, e.g. propane  C 3 H 8   How many such compounds could exist? In principle, an infinite number In reality, a vast unknown number
[object Object],[object Object],[object Object],[object Object],These are known as  alkanes   C 2 H 6 ethane C 3 H 8 propane C n H 2n+2 General formula for alkanes
n 1 2 3 4 5 6 Molecular Formula CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12 C 6 H 14 Structural formula Name methane ethane propane butane pentane hexane Condensed structural  formula
Further members of the series Heptane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Octane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Nonane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Decane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Undecane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Dodecane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Etc., etc.
Some points concerning this series of alkanes   1. Series is generated by repeatedly adding  ‘CH 2 ’  to the previous member of the series   A series generated in this manner is known as an  homologous series 2.  Nomenclature  (naming)   Names all share a common suffix, i.e.’ …ane’ The suffix ‘…ane’ indicates that the compound is an alkane The prefix indicates the  number of carbons in the compound
‘ Meth…’ = 1 Carbon ‘ Eth…’ = 2 Carbons ‘ Prop…’ = 3 Carbons ‘ But…’ = 4 Carbons ‘ Pent…’ = 5 Carbons ‘ Hex…’ = 6 Carbons ‘ Hept…’ = 7 Carbons ‘ Oct…’ = 8 Carbons ‘ Non…’ = 9 Carbons ‘ Dodec…’ = 12 Carbons ‘ Undec…’ = 11 Carbons ‘ Dec…’ = 10 Carbons Heptane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 ‘ Hept…’ implies 7 Carbons ‘… ane’ implies compound is an alkane
3. Representation and conformation ,[object Object],[object Object],Same structural formula Have the same information content
Propane  CH 3 -CH 2 -CH 3 Both  C-C  bonds identical Consider the different conformations that can arise during one full rotation about  C-C Energy maxima and minima: Staggered conformation (energy minimum) Eclipsed conformation (energy maxmium) Eclipsed conformation of propane possesses 14 kJ mol -1  of torsional strain energy relative to the staggered conformation 6 kJ mol -1 4 kJ mol -1 4 kJ mol -1
Torsional angle vs. strain energy plot similar to that of ethane ,[object Object],[object Object],[object Object],[object Object]
Butane  CH 3 -CH 2 -CH 2 -CH 3 Two equivalent terminal  C-C  bonds; one unique central  C-C  bond Conformations arising due to rotation about the terminal  C-C  bonds similar to those for propane Staggered  conformation Eclipsed conformation
φ  = 180  e.g. Define torsional angle  φ  as angle formed by terminal C-C bonds More complex for central C-C bond
One full 360   rotation about the central  C-C  of butane Pass through three staggered and three eclipsed conformations No longer equivalent Staggered conformations φ  = 180  Unique conformation Anti-periplanar conformation (ap) φ  = 60  [&  φ  = 300  ] Two equivalent conformations Gauche  or  synclinal conformations (sc) 3.8 kJ mol -1  steric strain energy
Eclipsed conformations φ  = 120  [&  φ  = 240  ] Two equivalent conformations Anticlinal conformations (ac) Strain energy = 16 kJ mol -1 φ  = 0  Unique conformation Syn-periplanar conformation (sp) Strain energy = 19 kJ mol -1 6 kJ mol -1 6 kJ mol -1 4 kJ mol -1 4 kJ mol -1 4 kJ mol -1 11 kJ mol -1
Torsional angle  vs.  strain energy plot
Syn-periplanar  conformation: global energy maximum Anti-periplana r conformation: global energy minimum Synclinal  and  anticlinal  conformations: local energy minima and maxima respectively  Energy barrier to rotation = 19 kJ mol -1 Too low to prevent free rotation at room temperature Sample of butane at 25  C (gas) At any instant in time: ~ 75% of the molecules in the sample will exist in the  anti-periplanar  conformation ~ 25% of the molecules in the sample will exist in the  synclinal  conformation < 1% will exist in all other conformations
Simple alkanes have conformational freedom at room temperature i.e. have rotation about  C-C  bonds the most stable (lowest energy) conformation for these is the all staggered ‘straight chain’ e.g. for hexane
4. Representing larger molecules Full structural formula for, e.g. octane Condensed structural formula Line segment structural formula
Line segment structural formula for octane ,[object Object],[object Object],[object Object],[object Object]
Generating the series of alkanes by incrementally adding ‘ CH 2 ’ However, the last increment could also give
Structural isomers   ‘ Isomer’, from Greek  isos  (equal) and  meros  (in part) ,[object Object],[object Object],[object Object]
[object Object],[object Object]
Extent of structural isomerism in alkanes   Alkane No. of structural isomers Methane 1 Ethane 1 Propane 1 Butane 2 Pentane 3 Hexane 5 Decane 75 Pentadecane 4347 Eicosane 366,319 Triacontane 44 x 10 9 (C 30 H 62 ) All known
Pentane  C 5 H 12 3 structural isomers ,[object Object],[object Object]
Need to expand the system of  nomenclature  to allow naming of individual structural isomers ,[object Object],[object Object],[object Object],[object Object],[object Object]
Alkane Alkyl group Methane Methyl (CH 3 -) Ethane Ethyl (CH 3 CH 2 -) Propane Propyl (CH 3 CH 2 CH 2 -) Butane Butyl (CH 3 CH 2 CH 2 CH 2 -) Etc. 2-Methylbutane [Straight chain numbered so as to give the lower branch number]
First, identify longest straight chain Number so as to give lower numbers for branch points Branches at C3 and C6 Not at C4 and C7 3,6-Dimethyl-6-ethylnonane ‘… nonane’
[object Object],[object Object],[object Object],[object Object],Substituents named in alphabetical order
 

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Organic chemistry 1-090211-1419

  • 1. CM1000, CM1002, CM2101 First file of lecture overheads for Organic Chemistry now available First Organic Chemistry lecture: Monday February 2 (Week 24) To access file: http://chemweb.ucc.ie Undergraduate 1st Year CM1000 Lecture Notes [Scroll down to 'Dr. Humphrey Moynihan'] Lecture Package 1 Lecture Package 2 Lecture Package 3
  • 2.
  • 3. Organic Chemistry 1 Part 1 of an introductory course in organic chemistry for CM1000, CM1002, CM2101 and related modules Dr. Humphrey A. Moynihan Kane Bldg 410 [email_address]
  • 4.
  • 5.
  • 6.
  • 7.
  • 8.
  • 9.
  • 10.
  • 11.
  • 12. Galactose: a sugar obtained from milk Molecular weight = 180.156 g mol -1 Using elemental (combustion) analysis: a worked example What is the Molecular Formula? Carry out elemental analysis Galactose 0.1000 g Combustion CO 2 0.1450 g + H 2 O 0.0590 g + O 2 0.0540 g Mol. Wt. / g mol -1 44 18 32 No. of moles 0.0033 0.0033 0.0017 1C 2H 1O Empirical Formula = CH 2 O
  • 13. Molecular Formula = (CH 2 O) n Mol. Wt. “ CH 2 O ” = 30.026 g mol -1 Mol. Wt. galactose = 180.156 g mol -1  n = 6 i.e. Molecular Formula = C 6 H 12 O 6 %C = 6 x 12.011 180.156 x 100 Atomic Wts. C: 12.011; H: 1.008; O: 15.999 = 40.00% Likewise: %H = 12 x 1.008 180.156 x 100 = 6.71% %O = 6 x 15.999 180.156 x 100 = 53.28%
  • 14. Galactose C: 40.00% H: 6.71% O: 53.28% Elemental analysis data presented in this way Can use as an experimental measure of purity A pure material should return elemental analysis data which is within ±0. 30% for each element E.g. given two samples of galactose Sample 1 C: 39.32% H: 7.18% O: 53.50% Sample impure Sample 2 C: 40.11% H: 6.70% O: 53.19% Sample pure
  • 15.
  • 16. Molecular formula : gives the identity and number of different atoms comprising a molecule Ethane: molecular formula = C 2 H 6 Valency: Carbon 4 Hydrogen 1 Combining this information, can propose i.e. a structural formula for ethane
  • 17.
  • 18.
  • 19. 109.5  109.5  109.5  109.5  Need to be able to represent 3D molecular structure in 2D
  • 21. Angle between any two bonds at a Carbon atom = 109.5 o
  • 22.
  • 23.
  • 24. Electronic configuration of Carbon C 1s 2 2s 2 2p 2 Hydrogen H 1s 1
  • 25.
  • 26. Bonding in ethane Atomic orbitals available: 2 Carbons, both contributing 4 sp 3 hybridised orbitals 6 Hydrogens, each contributing an s orbital Total atomic orbitals = 14 Combine to give 14 molecular orbitals 7 Bonding molecular orbitals; 7 anti-bonding molecular orbitals Electrons available to occupy molecular orbitals One for each sp 3 orbital on Carbon; one for each s orbital on Hydrogen = 14 Just enough to fully occupy the bonding molecular orbitals Anti-bonding molecular orbitals not occupied
  • 27. Ethane: molecular orbital diagram  molecular orbitals: symmetrical about the bond axis
  • 28. Four sp 3 hybridised orbitals can be arrayed to give tetrahedral geometry sp 3 hybridised orbitals from two Carbon atoms can overlap to form a Carbon-Carbon  bond C-C  bond Each sp 3 orbital contributes one electron to form C-C [C .. C] Visualising the molecular orbitals in ethane
  • 29. An s p 3 orbital extends mainly in one direction from the nucleus and forms bonds with other atoms in that direction.
  • 30. Carbon sp 3 orbitals can overlap with Hydrogen 1s orbitals to form Carbon-Hydrogen  bonds  bonds: symmetrical about the bond axis [Anti-bonding orbitals also formed; not occupied by electrons] Each sp 3 orbital contributes one electron; each s orbital contributes one electron to form C-H [C .. H]
  • 31. Geometry of Carbon in ethane is tetrahedral and is based upon sp 3 hybridisation sp 3 hybridised Carbon = tetrahedral Carbon Tetrahedral angle  109.5 o
  • 32. This represents a particular orientation of the C-H bonds on adjacent Carbons View along C-C bond: Newman projection Can select one C-H bond on either carbon and define a dihedral angle or torsional angle ( φ ) φ
  • 33.  
  • 34. φ = 60 o Staggered conformation Minimum energy conformation (least crowded possible conformation) C-C  bonds: symmetrical about the bond axes. In principle, no barrier to rotation about C-C bond Could have φ = 0 o Eclipsed conformation Maximum energy conformation (most crowded possible conformation) =
  • 35.
  • 36.
  • 37. φ = 0  Rotate 60  Eclipsed conformation strain energy 12 kJ mol -1 φ = 60  Staggered conformation strain energy 0 kJ mol -1 Rotate 60  φ = 120  Eclipsed conformation strain energy 12 kJ mol -1
  • 38. Rotate 60  φ = 180  Staggered conformation strain energy 0 kJ mol -1 Rotate 60  φ = 240  Eclipsed conformation strain energy 12 kJ mol -1 Rotate 60 
  • 39.
  • 40. Can plot torsional angle φ as a function of strain energy 12 kJ mol -1 = energy barrier to rotation about the C-C bond in ethane Too low to prevent free rotation at room temperature
  • 41.
  • 42.
  • 43. n 1 2 3 4 5 6 Molecular Formula CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12 C 6 H 14 Structural formula Name methane ethane propane butane pentane hexane Condensed structural formula
  • 44. Further members of the series Heptane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Octane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Nonane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Decane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Undecane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Dodecane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Etc., etc.
  • 45. Some points concerning this series of alkanes 1. Series is generated by repeatedly adding ‘CH 2 ’ to the previous member of the series A series generated in this manner is known as an homologous series 2. Nomenclature (naming) Names all share a common suffix, i.e.’ …ane’ The suffix ‘…ane’ indicates that the compound is an alkane The prefix indicates the number of carbons in the compound
  • 46. ‘ Meth…’ = 1 Carbon ‘ Eth…’ = 2 Carbons ‘ Prop…’ = 3 Carbons ‘ But…’ = 4 Carbons ‘ Pent…’ = 5 Carbons ‘ Hex…’ = 6 Carbons ‘ Hept…’ = 7 Carbons ‘ Oct…’ = 8 Carbons ‘ Non…’ = 9 Carbons ‘ Dodec…’ = 12 Carbons ‘ Undec…’ = 11 Carbons ‘ Dec…’ = 10 Carbons Heptane CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 ‘ Hept…’ implies 7 Carbons ‘… ane’ implies compound is an alkane
  • 47.
  • 48. Propane CH 3 -CH 2 -CH 3 Both C-C bonds identical Consider the different conformations that can arise during one full rotation about C-C Energy maxima and minima: Staggered conformation (energy minimum) Eclipsed conformation (energy maxmium) Eclipsed conformation of propane possesses 14 kJ mol -1 of torsional strain energy relative to the staggered conformation 6 kJ mol -1 4 kJ mol -1 4 kJ mol -1
  • 49.
  • 50. Butane CH 3 -CH 2 -CH 2 -CH 3 Two equivalent terminal C-C bonds; one unique central C-C bond Conformations arising due to rotation about the terminal C-C bonds similar to those for propane Staggered conformation Eclipsed conformation
  • 51. φ = 180  e.g. Define torsional angle φ as angle formed by terminal C-C bonds More complex for central C-C bond
  • 52. One full 360  rotation about the central C-C of butane Pass through three staggered and three eclipsed conformations No longer equivalent Staggered conformations φ = 180  Unique conformation Anti-periplanar conformation (ap) φ = 60  [& φ = 300  ] Two equivalent conformations Gauche or synclinal conformations (sc) 3.8 kJ mol -1 steric strain energy
  • 53. Eclipsed conformations φ = 120  [& φ = 240  ] Two equivalent conformations Anticlinal conformations (ac) Strain energy = 16 kJ mol -1 φ = 0  Unique conformation Syn-periplanar conformation (sp) Strain energy = 19 kJ mol -1 6 kJ mol -1 6 kJ mol -1 4 kJ mol -1 4 kJ mol -1 4 kJ mol -1 11 kJ mol -1
  • 54. Torsional angle vs. strain energy plot
  • 55. Syn-periplanar conformation: global energy maximum Anti-periplana r conformation: global energy minimum Synclinal and anticlinal conformations: local energy minima and maxima respectively Energy barrier to rotation = 19 kJ mol -1 Too low to prevent free rotation at room temperature Sample of butane at 25  C (gas) At any instant in time: ~ 75% of the molecules in the sample will exist in the anti-periplanar conformation ~ 25% of the molecules in the sample will exist in the synclinal conformation < 1% will exist in all other conformations
  • 56. Simple alkanes have conformational freedom at room temperature i.e. have rotation about C-C bonds the most stable (lowest energy) conformation for these is the all staggered ‘straight chain’ e.g. for hexane
  • 57. 4. Representing larger molecules Full structural formula for, e.g. octane Condensed structural formula Line segment structural formula
  • 58.
  • 59. Generating the series of alkanes by incrementally adding ‘ CH 2 ’ However, the last increment could also give
  • 60.
  • 61.
  • 62. Extent of structural isomerism in alkanes Alkane No. of structural isomers Methane 1 Ethane 1 Propane 1 Butane 2 Pentane 3 Hexane 5 Decane 75 Pentadecane 4347 Eicosane 366,319 Triacontane 44 x 10 9 (C 30 H 62 ) All known
  • 63.
  • 64.
  • 65. Alkane Alkyl group Methane Methyl (CH 3 -) Ethane Ethyl (CH 3 CH 2 -) Propane Propyl (CH 3 CH 2 CH 2 -) Butane Butyl (CH 3 CH 2 CH 2 CH 2 -) Etc. 2-Methylbutane [Straight chain numbered so as to give the lower branch number]
  • 66. First, identify longest straight chain Number so as to give lower numbers for branch points Branches at C3 and C6 Not at C4 and C7 3,6-Dimethyl-6-ethylnonane ‘… nonane’
  • 67.
  • 68.