chapter 12

Question 1

radical stability

Answer 1

more substituted the radical is, the more stable it is (same as carbocation)

benzylic ~ alylic > 3 > 2 > 1 > methyl

Question 2

general radical reaction:
alkane or alkene + radical initiator/energy —->

Answer 2

alkyl halide or alkenyl halide

Question 3

free radical chlorination:
alkane + Cl2, hv or heat —>
-how to determine where to put Cl

Answer 3

alkyl chloride
-determine all types of H and how many
- primary=1, secondary=3.8, tertiary=5
-highest % = major product

Question 4

free radical bromination:
alkane + Br2, hv or heat —>
-how to determine where to put Br

Answer 4

alkyl bromide
-major product = most substituted hydrogen is replaced with the bromine

Question 5

free radical halogenation mechanism:
-initiation
-propagation
-termination

Answer 5

-1 neutral molecule —> 2 radical species
-1 neutral molecule + 1 radical molecule —>1 neutral molecule + 1 radical molecule until product is formed
-2 radical molecules —> 1 neutral molecule

Question 6

allylic (or benzylic) bromination with NBS:
alkene + NBS,H2O2, hv or heat —>
-how to determine where to put Br
-major kinetic v.s major thermodynamic

Answer 6

alkenyl bromide (keeps double bond)
-replaces allylic or benzylic hydrogen with a bromine
-add radical at allylic hydrogen A and allylic hydrogen B
-resonate to find the major products
-major kinetic = product from most substituted radical intermediate
-major thermodynamic = most substituted double bond

Question 7

HBr with peroxides:
alkene + HBr,H2O2 —>
-how to determine where to put Br

Answer 7

alkyl bromide
-bromine adds to the least substituted side of the alkene (anti-markov)