Week 6: Alkane Rxns

Question 1

what is an alkane?

Answer 1

a hydrocarbon with no pi bonds

Question 2

are alkanes generally reactive?

Answer 2

no

Question 3

what is bond dissociation energy?

Answer 3

energy required to break a bond

Question 4

alkanes are easier to radicalize when their bonds are weak. what 3 factors make those bonds weak?

Answer 4

1. bond dissociation energy is small
2. bond length is long/thing carbon is bonded to is big
3. bond involves large charge separation

Question 5

when is a radicalized alkane more stable than a regular alkane?

Answer 5

When the radical is formed on a tertiary carbon. Or a secondary carbon, but less so. Sometimes on a primary carbon, but hardly ever.

Question 6

why are methyl groups never radicalized?

Answer 6

bond dissociation every is too high

Question 7

what’s the difference between regular resonance and radical resonance?

Answer 7

with radical resonance, you only move one electron at a time (rather that a pair)

Question 8

what 2 phenomena stabilize radicals?

Answer 8

1. hyperconjugation

2. resonance

Question 9

how does conjugation stabilize radicals?

Answer 9

when a radical/electron occurs on a carbon, the radical’s sp3 distorts/spreads out to fill empty space (causing the hybridization to be mostly planar).

In addition, the sp3 orbitals of the carbons the radicalized carbon is connected to move around/realign/overlap to help delocalize the radical charge

Question 10

How many steps does it take to radicalize an alkane?

Answer 10

3 (initiation, propagation, and termination)

Question 11

what must always be produced during the propagation stage of an alkane halogenation reaction?

Answer 11

new radical must be created (consistent with the products shown in the net reaction)

Question 12

why aren’t fluorine and iodine good halogens for alkane halogenation?

Answer 12

F is too exothermic and I is too endothermic