bromination of arenes

general reaction

initiation

propagation

termination

hydrogen is also?

a functional group

what is a useful reaction

- need to be able to predict reaction

- want only a few final products

propane reacting with Cl2

if propane reacting with Cl2 is random, what is ratio between 2-chloropropane and 1-chloropropane

2:6 (bc of hydrogens)

if propane reacting with Cl2 is not random, what is ratio between 2-chloropropane and 1-chloropropane

55%:45%, there is a control mechanism

if there is control mechanism?

gives us tool to be able to predict reaction + results

control mechanism for this reaction is?

stability of free radical (more stable when radical is more substituted)

propane with Br2 not random ratio?

97%:3%

is Br2 reaction useful?

yes, bc it preferentially reacts w/secondary H

why use Br2 than Cl2?

Br2 reacts more selectively with secondary H + make more stable molecule

toluene

ethylbenzene

i-propylbenzene

t-butylbenzene

aromatic hydrogen

C-H where carbon is involved in aromatic ring

aliphatic hydrogen

sp3 hybridized carbon bonded to hydrogen and is only bonded to other sp3 carbons

benzylic hydrogen

hydrogen bonded so sp3 carbon + carbon is bonded to aromatic ring

reactivity ranking from least to most

aromatic, aliphatic, benzyllic (1, 2, 3)

aliphatic hydrogens only have what kind of carbons

primary

benzylic hydrogen have what kind of carbons

primary, secondary, and tertiary

why a substitution happens to an aliphatic H

because the C-H bond is relatively weak compared to the new bonds formed, and the carbon center often develops an electrophilic character, driving molecule to react with attacking species to reach a more stable state

why substitution happens in arenes

- Aromatic rings are highly stabilized by aromaticity

- resist addition reactions because addition would destroy aromaticity

why substitution happens in benzylic

Because benzylic radicals are resonance-stabilized