Nomenclature and isomerism in organic chemistry

revision cards bases on AQA unit 4 Nomenclature and isomerism in organic chem part of the syllabus.

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Naming organic compounds

Carbon atoms

  • meth- = 1
  • eth- = 2
  • prop- = 3
  • but- = 4
  • pent- = 5
  • hex- = 6

Carbon bonds

  • -an- = only C-C bonds
  • -en = C=C boond
  • methyl- = CH3
  • ethyl - = CH3CH2
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Naming organic compounds

  • Cyclo- = carbon atoms bonded in a ring
  • Alkenes = C=C in compound
  • chloro-, floro-, bromo-, iodo- = a halogen attachment (haloalkanes)
  • -OH group = alcohol
  • -COH = -al = aldehydes
  • RR'CO = -one = ketones
  • -COOH = -oic acid = carboxilic acids
  • x-COOx = Ester (x not H atom)
  • -COCl = -oyl chloride = acyl chloride
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asymmetic carbon atoms are chiral and produces opt

  • Chiral
    • 'handed' exists in two mirror image forms that are not super-imposable
    • carbon bonded to 4 different groups = chiral centre
    • all amino acids (except glycerine) are chiral
    • lactic acid is also chiral
  • Effects on plane polarised
    • when light passes through a polaroid all vibrations in the select plane are cut.
  • Optical rotation can be measured using a polimeter
    • polarised light through two solutions of the same conc, each containing a different optical isomer of the same substance
    • one solution will rotate the plane of polarisation through a particular angle, clockwise (+ isomer)
    • The other will rotate the plane of polarisation by the same angle, anticlockwise (-isomer)
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Important definitions

  • enantomer = one of the pair of non-super impossible mirror image isomers.
  • Racemate
    • great many of reactions in organic synthesis produce optically active compounds are a 50:50 mixture of two optical isomers
    • racemate mixture
    • not optically active because effects of the two isomers cancel out.
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Why racemates are formed

  • e.g. 2-hydroxypropanoic acid (lactic acid)
    • C3O3H7 --> made in two stages from ethanal
    • Stage 1: H3CHCO + HCN- --> H3CHCCNO- + H+ --> H3CHCCNOH
      • carbon length of product greater than starting material
      • product has chiral centre. The :CN- group will add on with equal probability from above or below
      • this produces racemate mixture.
    • Stage 2: H3CHCCNOH +HCl +2H2O --> H3CCHCOOHH + NH4Cl
      • nitrile group converted to carboxylic acid group
      • hydrolysis reaction
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E-Z isomerism

  • positrons of substituents at either side of a C=C bond.
  • two subs may either be on same side of the bond (Z) or opp side (E)
  • No rotation around double bond.
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Optical isomerism

  • when 4 diff subs attach to carbon atom
  • two isomers are mirror images (not identical)
  • cannot superimpose one molecule onto another
  • optical isomers because they differ in the way they rotate the plane of polarisation of polarised light.
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Drug action determined by sterochemistry of molecu

  • some drugs optically active
  • Some purposes allow racemic mixture
  • others only require a specific one
  • One optical isomer may be effective, but the other may not be.
  • 3 options:
    • separate two isomers - difficult and expensive
    • sell mixture as a drug - wasteful as half inactive (ibuprofen sold as racemate)
    • design alternative synthesis that only makes required isomer
  • Some circumstances include the other isomers having unacceptable side effects
    • e.g. thalidomide
      • exists as pair as optical racemate
      • differ with how they interact with chiral molecules
      • isomers hard to separate so thalidomide supplies as racemate mixture
      • S form = birth defects
      • R form = safe sedative.
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Comments

lor

C=C double bond ending is ENE

e.g C2H2 IS ethene

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