Mechanisms Flashcards
4 types of mechanisms
Free radical substitution
Electrophilic addition
Nucleophilic substitution
Elimination reaction
free radical substitution steps
Initiation=X2>2X*
Propagation=X+hal*>(X-H*)+(H+hal)
(X-H*)+hal2>(X-H+hal)+hal*
Termination=hal*+hal*>hal2
unpaired electron represented by *nucleophilic substitution
halogen replaced by another group
halogenoalkanes undergo substitution reactions with nucleophiles
carbon-halogen bond broken(higher bond enthalpy=slower reaction)
bond enthalpy
the energy required to break a particular covalent bond in one mole of molecule in a gaseous state
nucleophiles
lone pair donors
OH-, aqueous, warm
CN-,ethanolic, warm
NH3,excess ammonia in ethanol
bonds in nucleophilic substitution
dative covalent
Can only have 4 bonds so halogen bond broken and electrons go to halogen
longer bond=weaker
electrophilic addition products
major product=tertiary carbocation,3 hydrocarbon chains, more stable carbocation
minor product-primary carbocation,1 hydrocarbon bond
electrophilic addition
C=C double bond v electron rich(due to cloud)
susceptible to electrophile attack
1 atom joins each side of double bond
electron rich double bond induces dipole-dipole
electrophile
lone pair acceptors
elimination reaction
when halogen and OH- ions react, elimination reaction can compete with nucleophilic substitution reaction
H and halogen removed from adjacent C atoms to give alkane
electrophilic addition basic
alkene>saturated compound
nucleophilic substitution basic
haloalkane>alcohol
elimination basic
haloalkane>alkene
free radical basic
+ haloalkane
UV light effect on O2
forms 2 oxygen free radicals that can react with molecular oxygen to form ozone
reversible reaction as natural formation/degradation by UV radiation
