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Reply 1

The benzene ring is hard to react due to the delocalised electron cloud that surrounds the ring.
But when you have a methyl group it has the same properties as anything, just a carbon hydrogen bond which will react more readily than the benzene ring.

Or do you need something more scientific?

Reply 2

the benzene ring is said to be activated.. it has a higher electron charge density :smile:

Reply 3

mgfrost
why is methylbenzene more reactive than benzene?

I know that the methyl group increases the reactivity of the benzene ring, particularly making it more succeptable to electrophilic attack, but why??

Although I haven't studied this unit yet, I presume it's because the methyl group causes the benzene ring to be branched, therefore the benzene rings do not pack as closely to one another as an un-branched ring might do. Consequently, the number of Van der Waals forces/ temporarily indued dipole induced dipole forces are lowered, thus the strength of the intermolecular bonds in methylbenzene are weaker, so it is more reactive than benzene.
I am merely speculating here - mind you! :biggrin:
Anyone care to criticse?

Reply 4

Can someone please explain the structure of a benzene ring and how exactly this 'delocalised cloud' of electrons is formed? I know it's got something to do with delocalised electrons in the p-orbitals of the C atoms or something.... Can someone explain?
Also, could someone just go through the whole benzene ring reactions quite briefly please?
Thanks! :smile:

Reply 5

Methylbenzene is more reactive because the C atom of the methyl group acts as an "electron pushing" group pushing the delocalised electrons one side leaving it more vunerable to electophilic attack.

Reply 6

Liamh32
Methylbenzene is more reactive because the C atom of the methyl group acts as an "electron pushing" group pushing the delocalised electrons one side leaving it more vunerable to electophilic attack.

If it does 'push' the delocalised electrons to one side somehow, then surely the Carbon is more vulnerable to nucleophilic attack, as it should have a delta positive charge? Doesn't a benzene ring undergo nucleophilic sub reactions?

Reply 7

Methyl groups are electron releasing. They release electrons through a conjugated effect so it increases the partial negative charge on benzene in the delocalised structure.

Reply 8

I'm doing Higher by the way, not A-level, so im really sorry if anything I say is just SQA info, anyway:


c
c
c c
c c
c

dolocalised electrons 'circling' above and below ring,
(1 hydrogen atom to each carbon - except the methyl group obviously; CH3)
benzene is unreactive because of it's incredibly strong structure,
however the methyl group in toluene has 3 H atoms (making it reactive) and if you think about the structure, the methyl group is alot easier for other substances to 'attack'

Reply 9

(i had arranged the 'C atoms' to show the structure btw, but after posting it all moved! argh!)

Reply 10

Butterfly Icing
I'm doing Higher by the way, not A-level, so im really sorry if anything I say is just SQA info, anyway:


c
c
c c
c c
c

dolocalised electrons 'circling' above and below ring,
(1 hydrogen atom to each carbon - except the methyl group obviously; CH3)
benzene is unreactive because of it's incredibly strong structure,
however the methyl group in toluene has 3 H atoms (making it reactive) and if you think about the structure, the methyl group is alot easier for other substances to 'attack'

oh yeah - the methyl group is pretty much 'sticking out' of the ring, increasing surface area, hence likelihood for attack!

Reply 11

Methylbenzene (toluene) is more reactive because the methyl group is electron donating (positive inductive effect) and thus makes the benzene ring more electron rich and so a better nucleophile to attack electrophiles in electrophilic substitution reactions.

Reply 12

Methyl is an eample of an electron donating group - so will increase the effective negative charge of the benzene ring.

I am sure you are aware of electron withdrawing groups - (flourine, oxygen), which would decreaase reactivity of the benzene ring.

Reply 13

ADREAM
Can someone please explain the structure of a benzene ring and how exactly this 'delocalised cloud' of electrons is formed? I know it's got something to do with delocalised electrons in the p-orbitals of the C atoms or something.... Can someone explain?
Also, could someone just go through the whole benzene ring reactions quite briefly please?
Thanks! :smile:


Although not strictly true, think of the ring containing alternating single/double C-C bonds. Basically, electrons are just shared between the carbons. Haven't done this for a while, forgot everything :rolleyes:

Reply 14

yosrush
Although not strictly true, think of the ring containing alternating single/double C-C bonds. Basically, electrons are just shared between the carbons. Haven't done this for a while, forgot everything :rolleyes:


OP - do not lissten to this / ignore it. You will not got any credit for the kekulee structure of benzene.

Reply 15

DeanK2
OP - do not lissten to this / ignore it. You will not got any credit for the kekulee structure of benzene.


Listen spelt with one s, Kekule without an extra e; brush up your spelling before you go slating people. I wasn't even answering the OP's question. All I was trying to say, it's easier to visualize and work with when you see it as swapping electrons (for example, when you add a new ion/molecule to the complex then it is goes around benzene ring and is thrown out afterwards but in that time no new compound can take its place).

Reply 16

yosrush
Listen spelt with one s, Kekule without an extra e; brush up your spelling before you go slating people. I wasn't even answering the OP's question. All I was trying to say, it's easier to visualize and work with when you see it as swapping electrons (for example, when you add a new ion/molecule to the complex then it is goes around benzene ring and is thrown out afterwards but in that time no new compound can take its place).


Wow - I spelt a word wrong. I think my Universities aren't even going to interview me now.

I wasn't slating you. It is outdated, old fashioned and irrelevant.

Hybridisation is the only way you should ever think - no resonance structures.

Reply 17

DeanK2
Hybridisation is the only way you should ever think - no resonance structures.


:rofl:

Although we know the structure of benzene is delocalised we draw kekule's structure at university and rationalise chemistry using resonance structures :smile:

Reply 18

EierVonSatan
:rofl:

Although we know the structure of benzene is delocalised we draw kekule's structure at university and rationalise chemistry using resonance structures :smile:


:eek: What!!

What is the point of learning deloocalization if we don't use it in organic chemistry?

Reply 19

EierVonSatan
Methylbenzene (toluene) is more reactive because the methyl group is electron donating (positive inductive effect) and thus makes the benzene ring more electron rich and so a better nucleophile to attack electrophiles in electrophilic substitution reactions.


This. The vast majority of the reactions of the benzene ring studied at A-Level are electrophilic substitutions. Anything that increases the electron density on the ring increases its susceptibility to attack.