General Flashcards
What is a substitution reaction?
This is the replacement of one group by another similar group
C-X bonds are generally polar and the nucleophile attacks the slightly positive carbon atom which leads to the nucleophile replacing the X in the halogenoalkene
What is an elimination reaction?
This is a reaction characterised by loss of a stable group or molecule and a change or hybridisation state of the carbon under attack from sp3 to sp2
What is an electrophile?
This is an electron deficient species that accepts electrons from an nucleophile
What is a nucleophile?
An electron rich species that donates electrons to electrophiles
What is a halogenoalkane?
These are a large class of compounds that contain an alkyl group (R) bonded to a halogen atom (X)
What reactions do halogenoalkanes undergo?
They undergo substitution reactions with nucleophiles/ bases through a process that can occur via an SN1 or SN2 pathways
Whether it undergoes substitution or elimination (loss of HX) depends on the structure of the halogenoalkane, reaction conditions and nature or Nu or base
Describe the electronic effects of an halogenoalkane
The halogen exerts a negative inductive effect due to its high electronegativity
This means the CX bond is polarised which means it can be attacked by nucleophiles
What did Hughes and Ingold do experimentally?
For a given substrate and a given nucleophile, they monitored the rate of reaction with respect to the concentration of substrate and nucleophile
What did Hughes and Ingold discover?
Most primary compounds undergo SN2 (couldn’t stabilise intermediate in SN1)
Secondary compounds have a choice of mechanism- depends on conditions
Most tertiary compounds undergo SN1 reactions
What is an SN1 reaction?
These reactions are stepwise reactions that occur in two steps
It involves an intermediate and not all bonds are broken and formed at the same time
What is an SN2 reaction?
These reactions are concerted
This is a chemical reaction in which all bond breaking and bond making occurs in a single step
Reactive intermediates are not involved
What is enantiomeric excess?
One enantiomer is present more than the other enantiomer
What conditions can dictate whether SN1 or SN2 react?
Solvent, temperature, nucleophile, leaving group, substrate, bond strength, leaving group
