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Organic Chemistry 1 An introductory course in organic chemistry by azaaaaa5

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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
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  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
            h.moynihan@ucc.ie
Late 18th century:
•Compounds from living organisms - Organic
•Compounds from lifeless matter – Inorganic
•Organic compounds thought to have „vital force‟

    Ammonium cyanate                        Urea
   (from mineral sources)               (from urine)
         ‘Inorganic’                      ‘Organic’

Wöhler 1828                      D
     Ammonium cyanate                         Urea
                               (Heat)


  •Discredited concept of „vital force‟
1800 on
•Elemental combustion analysis
•Identify and quantify elemental composition
•Provides empirical formulae

Lactic acid   from milk (i.e. „organic‟)

                Combustion
Lactic acid                           CO2      H 2O      O2

   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

                                      1C        2H       1O
•Lactic acid composed of Carbon, Hydrogen and Oxygen
•Fixed proportion: 1C:2H:1O
•Empirical formula: CH2O

•Majority of „organic‟ substances and many „inorganic‟
composed of Carbon, Hydrogen and maybe other elements

•Mid 19th Century: re-define organic substances
•Those composed of Carbon, Hydrogen (usually) and other
elements (maybe)

•1850-1860: Concept of Molecules
•Atoms of Carbon and other elements connected by covalent
bonds
•Hence, fixed proportions of elements
                                   C-C                  N-N           O-O
Bond Dissociation Energy
            (kJ mol-1)              348                 163           157

 •Carbon-Carbon bonds: especially strong covalent bonds
 •Carbon: unique in its ability to catenate
 •[can form chains of atoms]
 •Forms molecules composed of C-C bonds

        C                               C       C              C
                C       C           C       C       C         C   C
   C        C       C       C
                                            C                  C C
                                                C
       Linear molecules         Branched molecules       Cyclic molecules
•Organic molecules = Carbon-based molecules
•Organic chemistry = Chemistry of carbon-based molecules

Some properties of organic molecules
  •Stability: composed of stable C-C covalent bonds

  •Defined molecular structures
  •Defined three-dimensional shapes
       Some organic chemicals




            DNA                    Medicines
                                   •Active Pharmaceutical Ingredients
                                   •Excipients

                                    Fuels



Materials         Essential oils                        Pigments
    Organic chemicals make up
• Foods and foodstuff
• Flavours and fragrances
• Medicines
• Materials, polymers, plastics
• Plant, animal and microbial matter; natural
  products
• A vast range of manufactured goods
• [pharmaceuticals, foods, dyestuffs, adhesives, coatings,
  packaging, lubricants, cosmetics, films & fibres, etc. etc.]
   Socio-economic importance in
             Ireland
• Drugs/medicines: Pharmaceuticals
• Other organic products: Fine Chemicals
• Pharmaceutical & Fine Chemicals =
  PharmaChemical sector
• Ireland (2006) PharmaChemical exports:
  >€37bn
• ~ 40% of total manufacturing exports
• Employs ~ 20,000 – 50% of these graduates
• Ireland is one the No. 1 location for
  Pharmaceutical Investment in the EU
                                                 Gilead
                                                 Tyco
                                            Swords Labs




                                 Wyeth Biopharma
                                Takada

                            Takeda
                       Honeywell
                                                     Ipsen
           Alza

                                            >1,000
                                             500-1,000
                     Bausch & Lomb
           Genzyme                           100-500
 Cambrex
                                              1-100




Centocor
PharmaChemical manufacturing in
          Ireland
•   Main activity: manufacturing of APIs
•   [Active Pharmaceutical Ingredients]
•   Process scale organic chemistry
•   Process development & scale-up
•   Product finishing
             Stages of pharmaceutical
            development & manufacture
                         Phase I & II   Phase III
  Lead    Pre-Clinical    Clinical      Clinical    Launch &
Discovery Development      Trials        Trials     Manufacture



Research   Research & Development          Process Chemistry Optimisation & Support
   Organic        Organic Process
Drug Discovery       Chemistry
  Chemistry




  Emerging areas in Ireland                Current area of strength
                                                  in Ireland
Aspects of organic molecules
  Structure & bonding
  •Atom to atom connectivity
  •3D shape (Stereochemistry)
  •Naming (Nomenclature)

  Physical properties
  •Interaction with physical world

  Chemical properties
  •Transformation of molecular structure (Reactions)
  •How reactions occur (Mechanism)
                      Organic
                     Molecules



     Hydrocarbons                   Other classes of
      [C & H only]                 Organic Molecules

        HAM
                                      Dr. Stuart Collins
     Weeks 24-27
                                      Weeks 28-30,35

Textbook:   Organic Chemistry, A Short Course
            H. Hart, L. E. Craine, D. J. Hart and C. M. Hadad
   Learning Organic Chemistry
• Relatively low factual content
• Understanding concepts essential
• Value of the subject lies in application of
  concepts (problem solving)
• Lectures: presentation of key facts and concepts
• Tutorials/Workshops: application of concepts to
  problem solving
• Tutorials/Workshops an integral part of delivery
• Tues 1-2pm LL4 or Thurs 1-2pm FSB_A1
Using elemental (combustion) analysis: a worked example
Galactose: a sugar obtained from milk
Molecular weight = 180.156 g mol-1
What is the Molecular Formula?
Carry out elemental analysis

   Galactose      Combustion
                                      CO2    +   H 2O          O2
    0.1000 g                                            +
                                    0.1450 g   0.0590 g     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 =   CH2O
 Molecular Formula =   (CH2O)n
 Mol. Wt. “CH2O” = 30.026 g mol-1

Mol. Wt. galactose = 180.156 g mol-1  n = 6

 i.e. Molecular Formula =   C6H12O6
 Atomic Wts. C: 12.011; H: 1.008; O: 15.999

                        6 x 12.011
            %C =                       x 100     = 40.00%
                            180.156
Likewise:

       12 x 1.008                            6 x 15.999
%H =                x 100 = 6.71%     %O =                x 100 = 53.28%
       180.156                                180.156
Galactose     C: 40.00%      Elemental analysis data
              H: 6.71%
                             presented in this way
              O: 53.28%
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              Sample 2
            C: 39.32%             C: 40.11%
            H: 7.18%              H: 6.70%
            O: 53.50%             O: 53.19%
        Sample impure             Sample pure
Electronic configuration of Carbon   C 1s2 2s2 2p2
•Covalent bonds: sharing of electrons between atoms
•Carbon: can accept 4 electrons from other atoms
•i.e. Carbon is tetravalent (valency = 4)

Ethane: a gas (b.p. ~ -100oC)

Empircal formula (elemental combustion analysis):   CH3
i.e. an organic chemical
Measure molecular weight (e.g. by mass spectrometry):
30.070 g mol-1, i.e (CH3)n n = 2
Implies molecular formula =     C2H6
Molecular formula: gives the identity and number of
                   different atoms comprising a molecule

Ethane: molecular formula =   C 2H 6
Valency:      Carbon   4
              Hydrogen 1

Combining this information, can propose
                       H    H
                   H C      C H
                     H      H

i.e. a structural formula for ethane
•Each line represents a single covalent bond
•i.e. one shared pair of electrons
                       H     H

                H    C    C    H

                      H H
•Structural formulae present information on atom-to-
atom connectivity
•However, is an inadequate represention of some aspects of
the molecule


                    •Suggests molecule is planar
                    •Suggests different types of hydrogen
 Experimental evidence shows:
 •Ethane molecules not planar
 •All the hydrogens are equivalent
3 Dimensional shape of the molecule has tetrahedral carbons




  •Angle formed by any two bonds to any atom = ~ 109.5o
        109.5


                                              109.5
       109.5               109.5


Need to be able to represent 3D molecular structure in 2D

                   Bond coming out of plane of screen


                    Bond going into plane of screen
e.g.

               H         H
       =   H       C C       H
               H         H
Or

           H         H
                             H
       =       C C
           HH            H
Angle between any two bonds at a Carbon atom = 109.5o

   H        H
             H                             H        H
       C   C                                         H
  H                          109.5o            C   C
   H        H                          H
                                           H        H
                         o
                 109.5
Ethane: a gas b.p. ~ -100oC

Empirical formula: CH3        •An organic chemical
                              •Substance composed of
                              organic molecules

 Molecular formula C2H6       •Identity and number of atoms
                              comprising each molecule
                       H H
Structural formula
                     H C C H      •Atom-to-atom connectivity
                       H H
                                  H        H
Structural formula showing                  H
stereochemistry                       C   C     •3D shape
                                 H
                                  H        H
•Ethane: a substance composed of molecules of formula C2H6
•30.070 g of ethane (1 mole) contains 6.022 x 1023 molecules
(Avogadro‟s number)

•Can use the structural formula to show behaviour of
molecules
•Assume all molecules of a sample behave the same

•Sometimes need to consider behaviour of a population of
molecules
Electronic configuration of Carbon      C 1s2 2s2 2p2
                           Hydrogen         H      1s1
        H H
     H C C H
                     Orbitals available for covalent bonding?
        H H
      Ethane




             H 1s
            (1 e )          C 2py            C 2pz
                           (vacant)         (vacant)
•However, know that the geometry of the Carbons in ethane
is tetrahedral
•Cannot array py and pz orbitals to give tetrahedral geometry
•Need a modified set of atomic orbitals - hybridisation



        1s
                 2s       2p      2p       2p



                                 Hybridisation




        1s
                  sp3     sp3      sp3       sp3
       (2e-)
                 (1e-)   (1e-)   (1e-)      (1e-)
Bonding in ethane
 Atomic orbitals available:
 2 Carbons, both contributing 4 sp3 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 sp3 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

         *CH
                                                     *CC
                                                     H           H
                                                                     H
Energy                                                   C   C
                                                 H
                                                     H           H


                                                     CC
         CH

   molecular orbitals: symmetrical about the bond axis
Visualising the molecular orbitals in ethane
Four sp3 hybridised orbitals can be arrayed to give tetrahedral
geometry




sp3 hybridised orbitals from two Carbon atoms can overlap
to form a Carbon-Carbon  bond


                                      Each sp3 orbital
                                      contributes one electron

                                      to form C-C [C
                                                     ..C]
                   C-C  bond
    An sp3 orbital extends mainly in one
direction from the nucleus and forms bonds
     with other atoms in that direction.
Carbon sp3 orbitals can overlap with Hydrogen 1s orbitals to
form Carbon-Hydrogen  bonds


                                              H    H
                                                     H
                                        =       C C
                                             H
                                               H   H


Each sp3 orbital contributes one electron; each s orbital
contributes one electron to form C-H [C..H]

[Anti-bonding orbitals also formed; not occupied by electrons]

 bonds: symmetrical about the bond axis
Geometry of Carbon in ethane is tetrahedral and is based
upon sp3 hybridisation

sp3 hybridised Carbon = tetrahedral Carbon

Tetrahedral angle  109.5o
                                             109.5o
                                         C
   H         H
                 H
                       This represents a particular orientation
       C C
  H                    of the C-H bonds on adjacent Carbons
      H      H

       Ethane                                    H
                                            H            H
                 View along C-C bond:
                                             H        H
                                                 H
                                        Newman projection


Can select one C-H bond on either
                                                     φ
                                                             H
carbon and define a dihedral angle                   H           H
or torsional angle (φ)
                                                     H           H
                                                             H
                   H               Staggered conformation
               H          H        Minimum energy conformation
  φ =   60o
               H          H        (least crowded possible
                   H               conformation)

  C-C  bonds: symmetrical about the bond axes.
  In principle, no barrier to rotation about C-C bond
                              HH
                                                  H         H
Could have φ   = 0o                        =          C C
                                     H           H           H
                      H
                      H              H               H      H
                Eclipsed conformation
            Maximum energy conformation
         (most crowded possible conformation)
•Eclipsed conformation experiences steric hindrance

•Unfavourable interaction between groups which are close
together in space

           HH
                          Steric hindrance exists between
                          the eclipsing C-H bonds in this
                  H       conformation
      H
      H           H

•These unfavourable interactions absent in the staggered
conformation
•Hence, the staggered conformation is lower in energy
•Energy difference between eclipsed and staggered
conformations of ethane = 12 kJ mol-1
•Each C-H eclipsing interaction contributes 4 kJ mol-1 of
torsional strain energy
                          -1
                 4 kJ mol
                    HH
                                           Total: 12 kJ mol-1
                                           torsional strain

                H           H
                H           H              -1
           -1                   4 kJ mol
  4 kJ mol

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)
                 HH
                                Eclipsed conformation
 φ = 0                         strain energy 12 kJ mol-1
           H              H
           H              H

    Rotate 60
                 H
           H          H
φ = 60                       Staggered conformation
                              strain energy 0 kJ mol-1
           H          H
                 H
   Rotate 60

                HH
                                Eclipsed conformation
φ = 120                        strain energy 12 kJ mol-1
           H          H
           H          H
   Rotate 60
                H
           H         H    Staggered conformation
φ = 180                  strain energy 0 kJ mol-1
           H         H
                H
   Rotate 60

                HH
                         Eclipsed conformation
φ = 240                 strain energy 12 kJ mol-1
           H         H
           H         H
   Rotate 60
                             H
                       H          H   Staggered conformation
          φ = 300                    strain energy 0 kJ mol-1
                       H          H
                             H
                Rotate 60
                             HH     Eclipsed conformation
    φ = 360                        strain energy 12 kJ mol-1
   Full rotation
  Return to starting   H          H Identical to that at φ = 0
                       H          H
      position
Hence, in one full rotation about the C-C bond
•Pass through three equivalent eclipsed conformations
(energy maxima)
•Pass through three equivalent staggered conformations
(energy minima)
•Pass through an infinite number of other conformations
Can plot torsional angle φ as a function of strain energy

 Steric
 Strain
 Energy
/ kJ mol-1                                                    12 kJ mol-1



             0   60     120    180     240        300   360

                      Torsional angle / degrees


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 2H 6
•Contains Carbon and Hydrogen only (is a hydrocarbon)
•Contains  bonds only (C-C and C-H single bonds only)
•Contains only sp3 hybridised Carbon

Do other molecules exist which have these properties?
                                    H H H
 Yes, e.g. propane C3H8       H C C C H
                                H H H
How many such compounds could exist?
In principle, an infinite number
In reality, a vast unknown number
There exists a vast (and potentially infinite) number of
compounds consisting of molecules which:
•Contain only C and H
•Contain only  bonds
•Contain only sp3 hybridised C

These are known as alkanes

        C2H6           C3H8                CnH2n+2
        ethane         propane
                                       General formula
                                         for alkanes
                  Structural                   Condensed
n   Molecular     formula                      structural
                                Name
    Formula                                     formula
                  H
                H C H     methane              CH4
1   CH4           H
                  H H

    C2H6        H C C H     ethane             CH3CH3
2                 H H

                  H H H
                H C C C H      propane
3   C3H8          H H H
                                               CH3CH2CH3

                  H H H H
4   C4H10       H C C C C H     butane         CH3CH2CH2CH3
                  H H H H

                 H H H H H
5   C5H12   H C C C C C H            pentane   CH3CH2CH2CH2CH3
                 H H H H H

6   C6H14
                 H H H H H H
            H C C C C C C H           hexane   CH3CH2CH2CH2CH2CH3
              H H H H H H
Further members of the series

Heptane      CH3CH2CH2CH2CH2CH2CH3

Octane       CH3CH2CH2CH2CH2CH2CH2CH3

Nonane       CH3CH2CH2CH2CH2CH2CH2CH2CH3

Decane       CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3

Undecane     CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3

Dodecane     CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH3

Etc., etc.
Some points concerning this series of alkanes
1. Series is generated by repeatedly adding „CH2‟ 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            „Hept…‟ = 7 Carbons

 „Eth…‟ = 2 Carbons            „Oct…‟ = 8 Carbons

„Prop…‟ = 3 Carbons            „Non…‟ = 9 Carbons

 „But…‟ = 4 Carbons            „Dec…‟ = 10 Carbons

 „Pent…‟ = 5 Carbons         „Undec…‟ = 11 Carbons

 „Hex…‟ = 6 Carbons          „Dodec…‟ = 12 Carbons

    Heptane     CH3CH2CH2CH2CH2CH2CH3

„Hept…‟ implies 7 Carbons   „…ane‟ implies compound is
                                     an alkane
   3. Representation and conformation
      H H H H                  •Structural formulae: give
    H C C C C H
                               information on atom-to-atom
        H H H H
                               connectivity
            Butane
  (full structural formula)
                               •Do not give information on
                               stereochemistry
                                   H
             H
                                 H C H
           H C H                H               H H H H
         H H
                              H C C H         H C C C C H
       H C C C H                   H
                              H C H             H H H H
         H H H
                                H


Same structural formula          Have the same information content
  Propane CH3-CH2-CH3
  Both C-C bonds identical
  Consider the different conformations that can arise during
  one full rotation about C-C
  Energy maxima and minima:
                                        6 kJ mol-1
              CH3                         H CH3
         H          H

         H          H                H           H
              H            4 kJ mol-1 H         H 4 kJ mol-1
   Staggered conformation        Eclipsed conformation
      (energy minimum)           (energy maxmium)

Eclipsed conformation of propane possesses 14 kJ mol-1 of
torsional strain energy relative to the staggered conformation
Torsional angle vs. strain energy plot similar to that of ethane


  Steric
  Strain
 Energy                                                       14 kJ mol-1
/ kJ mol-1



             0   60      120     180    240       300   360

                      Torsional angle / degrees


    One full rotation about either C-C passes through:
    •three equivalent eclipsed conformations
    •three equivalent staggered conformations
    •Infinite number of other conformations
Butane CH3-CH2-CH2-CH3
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


            CH2CH3                     H CH2CH3
       H       H

       H         H               H           H
            H                     H         H
         Staggered                   Eclipsed
         conformation                conformation
More complex for central C-C bond


Define torsional angle φ as angle formed by terminal C-C bonds

e.g.
       CH3                           CH3        H
   H       H            o                           H
                    180                   C C
   H       H                         H
                                      H        CH3
       CH3
   φ = 180
One full 360 rotation about the central C-C of butane
Pass through three staggered and three eclipsed conformations
No longer equivalent
Staggered conformations
                   CH3
                            Unique conformation
               H       H
 φ = 180                   Anti-periplanar conformation (ap)
               H       H
                   CH3
                 CH 3
               H          Two equivalent conformations
  φ = 60            CH 3
                             Gauche or synclinal
[& φ = 300]                 conformations (sc)
               H       H
                   H         3.8 kJ mol-1 steric strain energy
Eclipsed conformations

                   6 kJ mol-1
  φ = 120          H CH3           Two equivalent conformations
[& φ = 240]                        Anticlinal conformations (ac)
                H        CH3        Strain energy = 16 kJ mol-1
                H       H
   4 kJ mol-1                 6 kJ mol-1

                11 kJ mol-1
                CH3 3
                  CH
  φ = 0                        Unique conformation
                                Syn-periplanar conformation (sp)
             H           H      Strain energy = 19 kJ mol-1
                        H
  4 kJ mol-1 H
                     4 kJ mol-1
Torsional angle vs. strain energy plot
             sp
                                                           sp
                           ac            ac
  Steric
  Strain
 Energy
/ kJ mol-1
                    sc                           sc
                                   ap

             0      60     120     180    240        300    360

                         Torsional angle / degrees
Syn-periplanar conformation: global energy maximum
Anti-periplanar 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‟

                         H H H H H H
  e.g. for hexane         C   C   C   H
                            C   C   C
                       H
                             H H HH H H
4. Representing larger molecules
Full structural formula for, e.g. octane

               H H H H H H H H
            H C C C C C C C C H
              H H H H H H H H

 Condensed structural formula

         CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3

 Line segment structural formula
                                     Line segment structural
                                     formula for octane

 •Each line represents a covalent bond between atoms
•Unless indicated otherwise, assume bonds are between Carbons
 •C-H bonds not shown, assume they are present
  •[so as make up valency of Carbon to 4]
                                       H H       H H
              O              =       H C C O C C H
                                       H H   H H


               =                 =            etc.   =   pentane
Generating the series of alkanes by incrementally adding „CH2‟
    H       'CH2'                         'CH2'        H H H
                            H H
 H C H                H C C H                        H C C C H
    H                       H H                        H H H

 Methane                    Ethane                    Propane

                    'CH2'           H H H H
                                  H C C C C H
                                     H H H H

                                      Butane
    However, the last increment could also give
                    'CH2'            H      H     H
                                  H C       C     C H
                                     H            H
                                         H C H
                                            H
                                         Isobutane
                                    H     H     H
           H H H H               H C      C     C H
         H C C C C H               H            H
           H H H H                      H C H
                                          H
          Butane (C4H10)
                                 Isobutane (C4H10)



                  Structural isomers

„Isomer‟, from Greek isos (equal) and meros (in part)
•Structural isomers: same molecular formulae

•Different structural formulae
(different atom-to-atom connectivity)
•Structural isomers: different physical properties
                                         CH3
      CH3 CH2 CH2 CH3              CH3 CH CH3

          n-butane                   isobutane
                    o
          b.p. - 0.5 C               b.p. - 12.0oC

•Are different chemical entities
Extent of structural isomerism in alkanes
  Alkane               No. of structural isomers
   Methane                    1
   Ethane                     1
   Propane                    1
   Butane                     2             All known
   Pentane                    3
   Hexane                     5

   Decane                     75
   Pentadecane                4347
   Eicosane                   366,319
  Triacontane                 44 x 109
  (C30H62)
Pentane C5H12               3 structural isomers

                                            CH3
 CH 3 CH 2 CH 2 CH 2 CH 3
                                    CH3 CH2 CH CH3
                    CH3
            CH3     C CH3
                    CH3
•All of these based on tetrahedral (sp3 hybridised) Carbon
•No other arrangements of C5H12 possible

Note
           CH3                                          CH3
CH3    CH2 CH CH3    =   CH3 CH CH2 CH3     =   CH3 CH2 CH
                             CH3                        CH3   etc.
 Need to expand the system of nomenclature to allow
 naming of individual structural isomers

•Compounds without branches are called „straight chain‟

 •Branched compounds are named as alkyl derivatives of the
 longest straight chain in the molecule
•The length of the longest chain provides the parent name
•The straight chain is numbered to allow indication of the point
of branching

•The branching alkyl groups (or substituents) are named
from the corresponding alkane
  Alkane              Alkyl group

  Methane             Methyl (CH3-)
  Ethane              Ethyl (CH3CH2-)
  Propane             Propyl (CH3CH2CH2-)
  Butane              Butyl (CH3CH2CH2CH2-)

  Etc.

                   CH3
         CH3   CH2 CH CH3           2-Methylbutane
         4     3   2   1

[Straight chain numbered so as to give the lower branch number]
                     CH3          CH3
           CH3 CH2 C CH2 CH2 C CH2 CH3
                   H         CH2 CH2 CH3

 First, identify longest straight chain
              CH3     CH3
    CH3 CH2 C CH2 CH2 C CH2 CH3                 „…nonane‟
            H         CH2 CH2 CH3

Number so as to give lower numbers for branch points

          CH3       CH3
           3         6                    Branches at C3 and C6
  CH3 CH2 C CH2 CH2 C CH2 CH3
  1   2   H 4   5   CH2 CH2 CH3           Not at C4 and C7
                    7   8   9

   3,6-Dimethyl-6-ethylnonane
Identical substituents grouped together with a prefix
•„di…‟ for two identical
•„tri…‟ for three
•„tetra…‟ for four

Substituents named in alphabetical order


        CH3     CH3                                CH3
                                 6   5   CH3 3
   CH3 C CH2 C CH3                      4           2
                                 CH3 CH2 C CH2     C CH3
       CH3   H                                        1
                                           CH2 CH3 H
 2,2,4-Trimethylpentane         2,4-dimethyl-4-ethylhexane

								
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