Organic Reactions and Mechanisms Chemistry^3 Mindmap

  • Created by: Strelly22
  • Created on: 17-12-22 10:03
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  • Organic Reactions and Mechanisms Part 1
    • Fundamental concepts
      • Heterolytic = unsymmetrical cleavage of a covalent bond
        • Polar reactions = formation of + cations and - anions
      • Homolytic = symmetrical cleavage of a covalent bond
        • radical = molecule with an unpaired reaction
      • Reaction Intermediates
        • sp3 carbon atom ?? sp2 carbon atom [carbocation] + eg. Br-
        • sp3 = pyramidal carbocation
        • sp2 = planar carbocation, planar carboanion, planar carbon radical
      • Double-headed arrow = movement of electrons in polar reactions
      • Single-headed arrow = movement of electrons in radical reactions
      • factors for electronic properties:
        • inductive effects = polarization of electrons through sigma bonds
          • -I = electron withdrawing
            • X = F, Cl, Br, OH, OR, CHO, COR, CN, CO2H, CO2R, NH2, NHR, NR2, NO2, SO3H
          • +I = electron donating
            • Z = R [alkyl], metals [Li, Mg]
        • hyperconjugation = delocalization of electrons by overlap of a sigma orbital with an empty p orbital
          • causes partial positive charges to develop on carbon atoms in the alkyl groups ? charge spread over larger area ? delocalization
        • mesomeric effects = delocalization of electron density through pi bonds
          • -M = electron acceptors containing a pi bond
            • COH, COR, COOH, COOR, NO2, CN, C6H6, CRCR2
          • +M = electron donors containing a lone pair or pi bonds
            • Cl, Br, OH, OR, SR, NH2, NR2, C6H6, CRCR2
        • generally +- M > +- I
        • conjugated molecules contain alternating single and double bonds
      • Steric effects = substituents can influence the stability and reactivity of a molecule
      • Steric hindrance / strain = size of substituents lowers reactivity of a particular site [increase = accelaration]
      • nucleophiles = electron donors [often -]
      • electrophiles = electron acceptors [often +]
      • nucleophilic site [e- rich] have: a heteroatom, a multiple C-C bond, carbon atom in a polar single bond
      • electrophilic site have: carbon atom in a polar single or multiple bond
      • Nucleophilic strength:
        • 1. charge: - charged ion is a stronger nucleophile than its conjugate acid
          • 2. electronegativity and electronic effects: highly electronegative atoms are weak nucleophiles
            • 3. polarizability: large nucleophilic sites are often strong nucleophiles
              • 4. solvation: anions are more nucleophilic in polar aprotic solvents than in polar protic solvents
      • Electrophilic strength:
        • 1. charge: a positively charged ion is a stronger electrophile than its conjugate base
          • 2. electronegativity and electronic effects: carbon atoms bonded to highly electronegative atoms are stronger electrophiles
      • Drawing reaction mechanism:
        • 1. draw skeletal structures and lone pairs
          • 2. identify any reactants or bases that are acids/bases
            • 3. identify which is electrophile and which is nucleophile
              • 4. draw a curly arrow from nucleophilic site to electrophilic site
                • 5. make sure the charges are correct, draw a 2nd curly arrow to accept the electrons from the bond
                  • 6. check overall product charge is the same as reactants
    • Reaction selectivity
      • Chemoselectivity = 1 FG reacts in preference to another FG
      • Regioselectivity = 1 position of a FG within an unsymmetrical molecule, reacts selectively over another
      • Stereoselectivity = 1 stereoisomer is formed selectively over others
        • Stereospecific reaction = different stereoisomers react differently


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