Radical Halogenation Flashcards
bond strength vs. size
bond strength goes down as size goes up
F > Cl > Br > I
strongest——weakest bond
dissociation energy vs. bond strength
DH goes down as bond strength is decreased
F > Cl > Br > I
highest DH—————————lowest DH
how is bond strength vs. size determined
bonds are stronger when overlapping orbitals are close in energy and size
bond strength vs. radical stability
bond strength goes down as radical stability goes up
CH4 > primary > secondary > tertiary
strongest———————-weakest bond
radical stability vs. DH
DH goes down as radical stability goes up
CH3 rad > primary rad > secondary rad > tertiary
highest DH—————————lowest DH
what hybrid orbital is a radical in?
sp2
what orbital is the single e- in a radical in?
unhybridized p
hyperconjugation
bonding e- in sigma bonds delocalize into the radical p orbital to stabilize
pyrolysis
if alkanes are heated to high temperatures all bonds rupture, and form higher and lower alkanes
hydrogen abstraction
a radical can remove a hydrogen from a carbon adjacent to the radical center to give an alkene
catalyst
speeds up pyrolysis and enhances selectivity
affects kinetics (rate) not thermodynamics
cracking
breaking an alkane into smaller fragments
early transition state
fast exothermic process
late transition state
slow, endothermic process
Hammond postulate
fast, exothermic reactions are characterized by early transition states, which are similar in structure to starting materials
slow, endothermic reactions have late (productlike) transition states
