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Polarity of a benzene ring?

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    anyone know?

    Thanks
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    I wouldn't have thought it had polarity...

    :confused:
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    it's not polar - there's a negative charge all over it because the 6 electrons are spread equally and the charge is distributed evenly. If there are substituents attached, such as a hydroxyl group, the molecule may become polar (I think)
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    it doesnt have polarity, the charge is the same throughout the ring because of the delocalised electrons
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    (Original post by Danielle89)
    it's not polar - there's a negative charge all over it because the 6 electrons are spread equally and the charge is distributed evenly. If there are substituents attached, such as a hydroxyl group, the molecule may become polar (I think)
    There's no negative charge on a benzene ring. It doesn't have a charge.
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    Benzene has no charge - nor permanent polarity.
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    (Original post by Kinkerz)
    There's no negative charge on a benzene ring. It doesn't have a charge.
    Edited cos Im being stupid, sorry!
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    right ok, thanks,

    SO a benzene ring has no polarity only when attached to another molecule, say it was attached to an ester and carboyxlic acid?
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    yup, i think if it was attached to the carboxylic acid, and it dissociated/ionised then there would be a difference in charge through the molecule and it would have some degree of polarity.
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    I'm trying to explain briefly why aspirin isn't addictive, have to talk about polarity of groups in the drug.

    Carboxylic acid is polar which means that molecule would dissolve in blood, now the ester group I am finding if that it is polar but it's polarity is very weak.... kinda in between maybe? these two are attached to a benzene ring
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    oooh, this is exciting. Well maybe not, but I need to know things like this for pharmacy. What are you studying btw?

    To cross the blood brain barrier and thus be addictive, the drug must be lipophilic/hydrophobic at some point in the body, obviously not happening with aspirin. But it must be polar at the part of the journey where it's dissolving in the blood. So I'd guess that the drug ionises at the carboxylic acid at the opposite end of the molecule to the benzene ring. Then when it gets to the blood brain barrier it cant cross it because the molecule is too hydrophilic i.e. polar, to cross the BBB. And I *think* thats why its not addictive.

    Dont quote me on that one outside tsr though
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    I'm studying this: http://www3.open.ac.uk/courses/bin/p12.dll?C01SK185

    Chemistry is a weak subject for me, i'm doing chemistry, maths and medical statistics at the 10 point level (level 1) and I hate them lol

    That's a great attempt at writing the answer and will help me a lot, thank you Danielle x
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    no problem, I need to know this sort of thing as a basis for my pharmacy degree anyway lol so you're helping me revise by asking that question Now back to molecular pharmacy hrm.

    Chemistry is a weak subject for me as well, I hate all the structures and trying to remember acidic/basic groups and whether groups are electron withdrawing or donating.

    Let me know if I was right haha
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    I think it might be true that it has to have some kind of non-polar polarity ( the ester group) so it can partly dissolve in the brain?
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    No, if it could dissolve in the blood brain barrier it WOULD be addictive.
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    It depends by your definition of polarity, it doesn't have polarity resulting from unequal distribution of electrons in bonds.

    However, there will be extreme and I mean extreme instantaneous dipole-induced dipoles as there are a great number of electrons in the compound. I suspect the forces between benzene are far greater than the H bonds in water, so benzene would be pretty insoluble
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    but anesthetics need to be able to enter the brain in order to work, I am getting advice tomorrow from a tutor will let you know
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    (Original post by Danielle89)
    No, if it could dissolve in the blood brain barrier it WOULD be addictive.
    Really? I thought aspirin was one of the few drugs that was small and non-polar enough to pass through the 'blood brain barrier'.

    Surely the condition for something to be chemically addictive is that it stimulates neuroreceptors in the brain? Such examples include Cocaine which is similar to dopamine, heroin to endorphins etc.?
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    (Original post by EierVonSatan)
    Really? I thought aspirin was one of the few drugs that was small and non-polar enough to pass through the 'blood brain barrier'.

    Surely the condition for something to be chemically addictive is that it stimulates neuroreceptors in the brain? Such examples include Cocaine which is similar to dopamine, heroin to endorphins etc.?
    Hmm... Well we know aspirin is insoluble, so it wouldn't really get through anything as a solute in water. I think you're right about the second paragraph, though. Hormones and drugs do act similarly.

    EDIT: Invented the term "non-soluble." Meant "insoluble". Fixed.
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    (Original post by JohnnyHouse)
    but anesthetics need to be able to enter the brain in order to work, I am getting advice tomorrow from a tutor will let you know
    ah, now I DO know about anaesthetics. The most likely mode of action is that there is a specific receptor located on the internal side of a sodium channel in any given membrane (not necessarily in the brain I dont think - not local anaesthetics anyway). To do this, the LA mostly ionises in the blood (some is unionised because the pKa of the drug is different to the pH of the blood and so it is only partially ionised). Because the drug exists in equilibrium in the blood, as the unionised drug dissolves in the membrane and leaves the blood, equilibrium re-establishes by more of the drug becoming unionising and crossing the membrane and so on until the majority of the drug has crossed the membrane to the receptor on the other side.

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Updated: January 10, 2009
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