Organic Reactions and Mechanisms Chemistry^3 Mindmap
- Created by: Strelly22
- Created on: 17-12-22 10:03
View mindmap
- 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]
- -I = electron withdrawing
- 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
- -M = electron acceptors containing a pi bond
- generally +- M > +- I
- conjugated molecules contain alternating single and double bonds
- inductive effects = polarization of electrons through sigma 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
- 3. polarizability: large nucleophilic sites are often strong nucleophiles
- 2. electronegativity and electronic effects: highly electronegative atoms are weak nucleophiles
- 1. charge: - charged ion is a stronger nucleophile than its conjugate acid
- 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
- 1. charge: a positively charged ion is a stronger electrophile than its conjugate base
- 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
- 5. make sure the charges are correct, draw a 2nd curly arrow to accept the electrons from the bond
- 4. draw a curly arrow from nucleophilic site to electrophilic site
- 3. identify which is electrophile and which is nucleophile
- 2. identify any reactants or bases that are acids/bases
- 1. draw skeletal structures and lone pairs
- Heterolytic = unsymmetrical cleavage of a covalent bond
- 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
- Fundamental concepts
Comments
No comments have yet been made