Help please on answering this benzene and phenol question please:)

the question is...'state and explain why electrophilic substitution reactions occur much more readily with phenol that with benzene'. It's worth 4 marks, anyone help with the answer please?
thank you :smile:

x x x

Reply 1

gooner88

10

Not sure how the mark scheme would have it but here's what I think.

Phenol is more reactive than benzene because:
-OH group on phenol activates the benzene ring.
-The lone pair on oxygen atom delocalises into the benzene ring.
-This increases the electron density in the ring.
-This attracts electrophiles more (more electrons available), therefore they are more likely to undergo electrophilic substitution reactions than benzene.

All of the above and...

The positively charged intermediate formed by electrophilic attack is further stabilised due to extra resonance involving the Oxygen of the OH group (it can be thought of as spreading the charge more around the molecule/ion) meaning that the energy barrier for intermediate formation is lower and therefore the process is easier for the phenol than the benzene.

Reply 3

stratomaster

gooner88

Not sure how the mark scheme would have it but here's what I think.

Phenol is more reactive than benzene because:
-OH group on phenol activates the benzene ring.
-The lone pair on oxygen atom delocalises into the benzene ring.
-This increases the electron density in the ring.
-This attracts electrophiles more (more electrons available), therefore they are more likely to undergo electrophilic substitution reactions than benzene.

Hmm coppied from jeffrowell.co.uk

Reply 4

gooner88

10

stratomaster

Hmm coppied from jeffrowell.co.uk

yep best source of revision for ocr chemistry, gets straight to the point without all the nonsense our teacher gives.
also just saw that now on june 2002 chains rings and spect paper.

Reply 5

stratomaster

gooner88

yep best source of revision for ocr chemistry, gets straight to the point without all the nonsense our teacher gives.
also just saw that now on june 2002 chains rings and spect paper.

Glad it is of help. Jeff Rowell was my A level chemistry teacher. That's how I recognised the notes lol!

Reply 6

gooner88

10

stratomaster

Glad it is of help. Jeff Rowell was my A level chemistry teacher. That's how I recognised the notes lol!

wow, really? you should thank him if u see him, its helped me greatly for the january exams. :smile:

if only i found the site last year, I might have got an A as As.

Reply 7

bjk

OP

thank you for the help :smile:

thats a good website as well
x x x

Reply 8

silent ninja

19

I would mention the obvious: the benzene ring pulls electrons from OH towards it i.e it has a negative inductive effect

silent ninja

I would mention the obvious: the benzene ring pulls electrons from OH towards it i.e it has a negative inductive effect

Thing is it doesnt!! If anything, oxygen would be expected to exert a -I influence on the ring due to its electronegativity.

The effect of the -OH group on the benzene ring is a +M effect not a +I effect i.e. activation through mesomeric interaction.

Benzene is not an electron attractor and there is no +I effect. The lone pair on the oxygen resonates into the ring - this is +M.

Help please on answering this benzene and phenol question please:)

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