Ch. 13 – Radical Chemistry

Question 1

What is a radical?

Answer 1

a reactive intermediate with single unpaired electron

Question 2

How are radicals formed?

Answer 2

homolysis of covalent bond by adding heat or light

Question 3

What is geometry and hybridization of carbon radical?

Answer 3

sp2, trig planar

Question 4

Cleavage of weaker bonds form _______ stable radicals (more or less).

Answer 4

more

Question 5

More stable radicals have ________ (more or less) subs.

Answer 5

more

Question 6

Why are more alkyl groups helpful for making more stable radicals?

Answer 6

they are more polarizable and donate electron density

Question 7

Where is the unpaired electron of a radical located?

Answer 7

in the unhybridized p orbital

Question 8

What is bond dissociation energy?

Answer 8

energy required to break a bon homolytically

Question 9

What is radical initiation?

Answer 9

formation of two radicals from sigma bond cleavage (sigma bond must be relatively weak)

Question 10

What is radical propogation?

Answer 10

one radical is consumed and another is formed

Question 11

What is radical propogation (hydrogen abstraction)?

Answer 11

pulling out elemental hydrogen and making new H-X bond

Question 12

What is radical propogation (addition to pi bond)?

Answer 12

addition of radical X dot to pi bond to from new C-X bond

Question 13

What is radical termination?

Answer 13

two radicals combine to form a sigma bond

Question 14

What is a radical initiator?

Answer 14

something with a weak bond that serves a source of radical and kick starts the reaction (RO-OR)

Question 15

Why is light or heat needed to make radicals?

Answer 15

energy is needed to break bonds

Question 16

How is an alkyl halide made from an alkane?

Answer 16

radical chemistry! by adding X2 and light or heat

Question 17

What is the selectivity of alkane radical reactions with Cl2 and Br2?

Answer 17

Br2 is selective

Cl2 is unselective

Question 18

Why is Cl2 so unselective?

Answer 18

H-abstraction is exothermic with Cl so poor selectivity is caused by hammond’s postulate… anything that would stabilize a radical is meaningless (you cant see what is on the other side of the hill)

Question 19

Why is light/heat needed for radical reactions?

Answer 19

provides energy for homolytic bond cleavage

Question 20

Do radicals rearrange?

Answer 20

NO

Question 21

What is the basis of propogation?

Answer 21

a radical reacts with another reagent to form a new sigma bond and another radical

Question 22

What is the basis of termination?

Answer 22

two radicals combine without generating more

Question 23

What is the trend for ease of radical formation?

Answer 23

3º-H will form radical quickest and most readily

Question 24

In chlorination, what substitution will form in greater abundance?

Answer 24

more sub’d carbon that Cl attaches to will form in greatest abundance but not by that much

Question 25

Why is bromination highly selective and what is it highly selective for?

Answer 25

highly selective for weakest (most sub’d) C-H bond because it will give most stable radical

bromination is exothermic overall but has endothermic transition state so it resembles products most. There is a greater energy barrier so it will form only the more stable radical

Question 26

What is the RDS of alkane halogenation?

Answer 26

hydrogen abstraction