Organic Chemistry: Structure and Nomenclature


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Organic chemistry for A-level
Structure and Nomenclature

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Organic Chemistry: Structure and Nomenclature

  1. 1. Organic Chemistry I Structure and Nomenclature Indra Yudhipratama
  2. 2. Outline  Representation of organic molecules  Nomenclature of organic chemistry  Structure of hydrocarbons (alkanes, alkenes, and alkynes) and aromatic benzene.  Isomerism
  3. 3. Representation of the Organic Molecules How to draw it? Mainly there are 4 ways to draw organic molecules CH3CH2CH2CH3 3D formula Skeletal Formulae Structural Formulae CH3 H5C2 H H
  4. 4. Representation of the Organic molecules  In this course, you are expected to understand the organic molecules in skeletal form.  How to draw skeletal form?  Draw H attached to O, N, S (or other elements except C)  Do not draw H attached to C (unless it is important)  Use uniform bond lengths (give your best effort)  Use uniform bond angles (give your best effort)  120o for single bond and double bonds  180o for triple bonds
  5. 5. Representation of the Organic molecules  Example:
  6. 6. Why skeletal formula? CH CH CH N CH CH2 CH2 CH2 CH3 C O O CH3 O C O C CH CH CH CH CH C C C N C C C C C C O O C O C O C C C C C C HH H H H H H H H H H H H H H H H H H H H
  7. 7. Why skeletal formula?  Just simply makes your life easier  With this structure you can easily spot the functional group and reaction centre N O O O O
  8. 8. Nomenclature  Select the longest continuous carbon chain.  This determines the base name.  Consider each branch and name similarly except change the name from –ane to –yl.  Number the C atoms so that substituents have the lowest possible number.
  9. 9. Nomenclature Name each substituent according to its identity and the number of the C atom to which it is attached.  Use di, tri, tetra as appropriate. Separate numbers from one another by commas. List substituents alphabetically by name.
  10. 10. Functional groups What is functional group? An atom or group of atoms which gives rise to an homologous series
  11. 11. Nomenclature example 4-propylcyclohex-2-en-1-one O Cl O O O cyclohexyl 4-methylhex-2-ynoate 1-chloropropan-2-one 3-ethyl-4,5-dimethyloctane
  12. 12. However,  More complicated organic molecule sometimes is known by its trivial name NOT IUPAC systematic name N O O O O methyl 8-methyl-3-[(phenylcarbonyl)oxy]-8- azabicyclo[3.2.1]octane-2-carboxylateCocaine
  13. 13. And a bit messy now … Calicheamicin 𝛾1 S-[(2R,3S,4S,6S)-6-({[(2R,3S,4S,5R,6R)-5-{[(2S,4S,5S)-5-(Ethylamino)-4- methoxytetrahydro-2H-pyran-2-yl]oxy}-4-hydroxy-6-{[(2S,5Z,9S,13E)-9-hydroxy-12- [(methoxycarbonyl)amino]-13-[2-(methyltrisulfanyl) ethylidene]-11- oxobicyclo[7.3.1]trideca-1(12),5-diene-3,7-diyn-2-yl]oxy}-2-methyltetrahydro-2H- pyran-3-yl]amino}oxy)-4-hydroxy-2-methyltetrahydro-2H-pyran-3-yl] 4- {[(2S,3R,4R,5S,6S)-3,5-dihydroxy-4-me thoxy-6-methyltetrahydro-2H-pyran-2- yl]oxy}-3-iodo-5,6-dimethoxy-2-methylbenzenecarbothioate
  14. 14. Structure of Hydrocarbons Alkanes (e.g. Ethane)  The carbon-carbon bond is made from overlap of two sp3 orbitals to form a s bond  The molecule is approximately tetrahedral around each carbon
  15. 15. Structure of Hydrocarbons Alkenes (e.g. Ethenes)  The geometry around each carbon is called trigonal planar  The three sp2 hybridized orbitals come from mixing one s and two p orbitals  One p orbital is left unhybridised  Restricted rotation due to overlap on p orbitals (π bonding). Result: Cis/trans isomerism
  16. 16. Benzene (delocalisation Structure)  Each carbon has p orbital that forms π bonding  The π bonds not only with the adjacent carbon, but with all carbon  π electrons are delocalised  give delocalisation structure  Delocalisation can takes place whenever two double bonds are separated by single bond or a lone pair is separated from a double bond by one single bond
  17. 17. Delocalisation structure
  18. 18. Structure of Hydrocarbon Alkynes (e.g. ethyne)  The arrangement of atoms around each carbon is linear with bond angles 180o  The carbon in ethyne is sp hybridized  One s and one p orbital are mixed to form two sp orbitals  Two p orbitals are left unhybridized  The triple bond consists of one s and two p bonds
  19. 19. Isomerism
  20. 20. Structural Isomer  Same chemical formula, but behave differently  The structure is different.  E.g. C4H10 It can be drawn in two ways: Quick Review: Name all the isomers of C4H10. CH3 CH3 CH3
  21. 21. Structural Isomer  E.g.  A organic molecule has formula C4H10O. It has isomers with alcohol FG: Quick Review: Draw the other isomer with alcohol FG and name it. OH OH C4H10OC4H10O
  22. 22. Structural Isomer  C4H10O also can be drawn with another functional group. Because they have different functional, so it’s called the functional group isomerism Quick Review: Name the functional group of those molecules above. OCH3 CH3 O CH3 CH3
  23. 23. Stereoisomerism  Related to the geometrical/spatial arrangement  Two types of stereoisomerism:  Cis/trans isomerism  occurs mainly at alkenes  Optical isomerism Chiral centre. CH3 CH3 CH3 CH3 trans-but-2-ene cis-but-2-ene COOH OH CH3 H HOOC OH CH3 H (2S)-2-hydroxypropanoic acid (2R)-2-hydroxypropanoic acid
  24. 24. Cis-trans isomers  Cis-trans isomers are the result of restricted rotation about double bonds  These isomers have the same connectivity of atoms and differ only in the arrangement of atoms in space  One molecule is designated cis (groups on same side) and the other is trans (groups on opposite side)  Cis-trans isomerism is not possible if one carbon of the double bond has two identical groups
  25. 25. Optical isomerism  What is Chiral Centre? A Carbon atom in a molecule attached to four different groups.  Chiral centre  Chiral molecules Cannot be superimposed, but are mirror images each others COOH OH CH3 H HOOC OH CH3 H (2S)-2-hydroxypropanoic acid (2R)-2-hydroxypropanoic acid
  26. 26.  Quick Review 9701/w11/p12
  27. 27. 9701/w11/p43/5c