Nomenclature and isomerism in organic chemistry

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

• 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

• 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)

• 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.

• 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

• 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.

• 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.

• 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.