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h99h20baby
Joined: 01 Jul 2007
Posts: 40
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 Posted: Tue Jul 24, 2007 9:38 am Post subject: Question 12 |
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Alcohols (1-butanol) have a partially negatively charged oxygen and a partially positively charged hydrogen which can engage in hydrogen bonding which increases the boiling point (CHM 4.2). Esters (ethyl acetate) have a partially negative oxygen but no partially positive hydrogen so no hydrogen bonding.
I thought esters could hydrogen bond just not to themselves? Could you explain the answer to this answer more clearly?
I read in #22 on physics Gs 5: that Ethers are water soluble because the oxygen in ether, which is covalently bonded to two carbons, can hydrogen bond with the hydrogen in H2O.
In Wikipedia it says: Ether molecules cannot form hydrogen bonds among each other
I am confused about h-bonds with respect to esters and ethers can you clarify? |
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admin
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Joined: 08 Dec 2003
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| Posted: Wed Jul 25, 2007 11:34 pm Post subject: |
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| Quote: | | I thought esters could hydrogen bond just not to themselves? |
True.
| Quote: | | I read in #22 on physics Gs 5: that Ethers are water soluble because the oxygen in ether, which is covalently bonded to two carbons, can hydrogen bond with the hydrogen in H2O. |
True.
| Quote: | | In Wikipedia it says: Ether molecules cannot form hydrogen bonds among each other |
True.
H2O is great an H-bonding because (1) each molecule has 2 partially positive H's and each oxygen is partially negative with 2 lone pairs of electrons ready to H-bond with 2 other molecules; (2) each O ends up almost in a tetrahedron surrounded by 4 H atoms: 2 covalent bonds and 2 H-bonds. Very efficient, very, very high boiling point as a result of these intermolecular bonds.
Alcohols are pretty good (not as good as water) since they have one partially +ve H and one partially -ve O: not bad. Esters and ethers have no intermolecular H bonds because they have a partially negative O but no partially positive H. IF there is another compound with a partially postive H, then it could bond to an ester or an ether but the boiling points of pure esthers or ethers will be much lower than the comparable alcohol.
Even if you mixed the 2 compounds, the alcohol still Hbonds more efficiently and as a compound its bp is higher because of H bonds.
www.chemguide.co.uk/atoms/bonding/hbond.html |
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admin
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| Posted: Thu Jul 30, 2009 3:08 pm Post subject: |
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