Radical Halogenation Flashcards Preview

Organic Chemistry I & II > Radical Halogenation > Flashcards

Flashcards in Radical Halogenation Deck (10)
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1
Q

Which is the least stable carbocation?

A

methylcarbocation (CH3+)

2
Q

As carbon chain in an alkane becomes longer, what happens to molecular stability?

A

Longer carbon chains increase stability of alkanes.

3
Q

What results from heterolytic bond cleavage of halogen molecules?

A

Two reactive free radicals are formed. (Chlorine example shown).

4
Q

What is a free radical?

A

A species with an unpaired electron.

5
Q

What is the first step in the general mechanism for free-radical halogenation?

A

Initiation: homolysis of a halogen molecule to form two halogen atoms, initiated by ultraviolet radiation or sunlight. A halogen atom has an unpaired electron and acts as a free radical. (Chlorination of methane shown).

6
Q

What is the second step in the general mechanism for free-radical halogenation?

A

Chain propagation: (two steps): a chlroine ion attracts a hydrogen atom away from methane (CH4) leaving a 1° methyl radical (CH3). The 1° methyl radical (CH3) then pulls a chlorine radical (Cl) from a different molecule of chlorine (Cl2), halogenating the methyl radical, but creating a new chlorine (Cl) radical. If there is sufficient chlorine, this process may repeat in a chain reaction until the third step in the general mechanism for free-radical halogenation.

7
Q

What is the third step in the general mechanism for free-radical halogenation?

A

Chain termination: recombination of two free radicals. Multiple recombination options exist, incliding two chlorine radicals (2 Cl) recombining to form molecular chlorine (Cl2); a chlorine radical (Cl) halogenating a previously deprotinated methyl radical (CH3) to form methane (Ch4); or two methane radiacals (CH3) reacting to form ethane (C2H6).

8
Q

Is it easier to cleave a hydrogen from an alkane heterolyrically or homolytically?

A

Alkanes prefer heterolytic bond cleavage.

9
Q

Is chloronation exothermic or endothermic?

A

exothermic

10
Q

Is bromination exothermic or endothermic?

A

Endothermic.