Essential ideas:
  • Key organic reaction types include nucleophilic substitution, electrophilic addition, electrophilic substitution and redox reactions. Reaction mechanisms vary and help in understanding the different types of reaction taking place.
  • Organic synthesis  is the systematic  preparation  of a compound  from a widely available starting material or the synthesis  of a compound  via a synthetic route that often can involve a series of different steps.
  • Stereoisomerism  involves isomers which have different arrangements  of atoms in space but do not differ in connectivity  or bond multiplicity (ie whether single, double or triple) between the isomers themselves.
20.1 - SN2 mechanism
Understandings:
SN2 represents a nucleophilic bimolecular substitution reaction.
SN2 involves a concerted reaction with a transition state.
For primary halogenoalkanes  the predominant mechanism is SN2. Both mechanisms occur for secondary halogenoalkanes.
For SN2, rate = k[halogenoalkane][nucleophile]. 
SN2 is stereospecific with an inversion of configuration at the carbon.
SN2 reactions are best conducted using aprotic, polar solvents.
Applications and skills:
Deduction of the mechanism of the nucleophilic substitution reactions of halogenoalkanes  with aqueous sodium hydroxide in terms of SN1 and SN2 mechanisms.
Outline of the difference between protic and aprotic solvents.
20.1 - SN1 mechanism
Understandings:
SN1 represents a nucleophilic unimolecular substitution reaction. 
SN1 involves a carbocation intermediate. 
For tertiary halogenoalkanes  the predominant mechanism is SN1
The rate determining step (slow step) in an SN1 reaction depends only on the concentration of the halogenoalkane,  rate = k[halogenoalkane]. 
SN1 reactions are best conducted using protic, polar solvents.
Applications and skills:
Deduction of the mechanism of the nucleophilic substitution reactions of halogenoalkanes  with aqueous sodium hydroxide in terms of SN1 and SN2 mechanisms. 
Outline of the difference between protic and aprotic solvents.
20.1 Choice of solvent for SN1 and SN2 reactions 
Understandings:
SN2 reactions are best conducted using aprotic, polar solvents.
SN1 reactions are best conducted using protic, polar solvents.
Applications and skills:
Outline of the difference between protic and aprotic solvents.
20.1 Stereochemistry of SN reactions 
This video covers the stereochemistry of SN1 and SN2 reactions.
20.1 Comparison on hydroxide ion and water molecule as nucleophiles 
Applications and skills:
Explanation of why hydroxide is a better nucleophile than water.
20.1 - Electrophilic addition reactions 
Applications and skills:
Electrophilic Addition Reactions:
Deduction of the mechanism of the electrophilic addition reactions of alkenes with halogens/interhalogens and hydrogen halides.
20.1 - Markovnikov's rule 
Practice worksheet
Understandings:
Markovnikov’s rule can be applied to predict the major product in electrophilic addition reactions of unsymmetrical alkenes with hydrogen halides and interhalogens. The formation of the major product can be explained in terms of the relative stability of possible carbocations in the reaction mechanism.
20.1 Nitration of benzene
Applications and skills:
Electrophilic Substitution Reactions:
 Deduction of the mechanism of the nitration (electrophilic substitution) reaction of benzene (using a mixture of concentrated nitric acid and sulfuric acid).
20.1 Reduction of carbonyl compounds 
Note: Various sources that I've seen have different conditions for the reaction, some state that the reaction proceeds at room temperature whereas the IB text that I have state it must be heated. I don't think it matters too much as long as you know the reducing agent for each reaction.
Understandings: 
Reduction Reactions:
Carboxylic acids can be reduced to primary alcohols (via the aldehyde).
Ketones can be reduced to secondary alcohols. Typical reducing agents are lithium aluminium hydride (used to reduce carboxylic acids) and sodium borohydride.
Applications and skills:
Writing reduction reactions of carbonyl containing compounds: aldehydes and ketones to primary and secondary alcohols and carboxylic acids to primary alcohols, using suitable reducing agents.
20.1 Reduction of nitrobenzene
Application and skills:
Reduction reactions
Conversion of nitrobenzene to phenylamine via a two-stage reaction.

 
20.2 Organic reaction pathways 
A summary of the reaction pathways in topic 10.1 and 20.1 (not including the reactions of benzene). 
Guidance:
Conversions with more than four stages will not be assessed in synthetic routes.
Reaction types can cover any of the reactions covered in topic 10 and sub-topic 20.1.
20.2 Retro-synthesis 
Understandings:
Retro-synthesis  of organic compounds.
Applications and skills:
Deduction of multi-step synthetic routes given starting reagents and the product(s).
Guidance:
Conversions with more than four stages will not be assessed in synthetic routes.
Reaction types can cover any of the reactions covered in topic 10 and sub-topic 20.1.
20.3 Introduction to isomerism 
Understandings:
Stereoisomers are subdivided into two classes—conformational isomers, which interconvert by rotation about a σ bond and configurational isomers that interconvert only by breaking and reforming a bond.
Configurational  isomers  are further subdivided  into cis-trans  and E/Z isomers and optical isomers.
20.3  cis-trans isomerism 
Understandings:
Cis-trans isomers can occur in alkenes or cycloalkanes (or heteroanalogues) and differ in the positions of atoms (or groups) relative to a reference plane. 
Applications and skills:
Construction of 3-D models (real or virtual) of a wide range of stereoisomers.
Guidance:
The term geometric isomers as recommended by IUPAC is now obsolete and cis-trans isomers and E/Z isomers should be encouraged in the teaching programme.
20.3 Physical properties of cis-trans isomers
This video covers the differences in melting point and boiling point between cis-trans isomers. 
20.3 E/Z isomerism 
Understandings:
According to IUPAC, E/Z isomers refer to alkenes of the form R1R2C=CR3R4 (R1 ≠ R2, R3 ≠ R4) where neither R1 nor R2 need be different from R3 or R4.
20.3 Optical isomerism - part 1
Understandings:
A chiral carbon is a carbon joined to four different atoms or groups.Optical isomers are enantiomers. Enantiomers are non-superimposeable  mirror images of each other. 
20.3 Optical isomerism part 2
Understandings:
An optically active compound can rotate the plane of polarized light as it passes through a solution of the compound.
A racemic mixture (or racemate) is a mixture of two enantiomers in equal amounts and is optically inactive.
Applications and skills:
Distinction between optical isomers using a polarimeter.
20.3 Diastereomers 
Understandings:
Diastereomers are not mirror images of each other.