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Organic Chemistry doubts!

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Guest KAPOWW!!

The textbook states water is a weaker nucleophile than OH- because it lacks a negative charge,

Doubt 1- How is water a nucleophile in the first place when it has no charge?

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The textbook states water is a weaker nucleophile than OH- because it lacks a negative charge,

Doubt 1- How is water a nucleophile in the first place when it has no charge?

Water is slightly polar, if I'm not mistaken. The Oxygen molecule is slightly negative, and the two Hydrogens are both ever so slightly positive. The hydrogens make hydrogen-bonds with other Oxygen. So then, there's like a magnet-like attraction between the H's and the O... which is called a Hydrogen bond.

Anyway, that's basically what I understood from your question :P

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Guest KAPOWW!!

[quote name=Cupcakes <3' timestamp='1315545977' post='130850]

The textbook states water is a weaker nucleophile than OH- because it lacks a negative charge,

Doubt 1- How is water a nucleophile in the first place when it has no charge?

Water is slightly polar, if I'm not mistaken. The Oxygen molecule is slightly negative, and the two Hydrogens are both ever so slightly positive. The hydrogens make hydrogen-bonds with other Oxygen. So then, there's like a magnet-like attraction between the H's and the O... which is called a Hydrogen bond.

Anyway, that's basically what I understood from your question :P

Thanks Cupcake, but that's not the question. Let me rephrase me question so I'm clear:

Doubt: Is water polar to qualify as a weak nucleophile? if so how?

You didn't missed the 'how so' part(let me justify- you explained intermolecular bonding between water molecules, what I want to know is what does water attribute its polar nature to? ,so, yeah call me a [email protected], I know your trying to help, much appreciated! :D Sorry!

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I don't remember learning this (is this HL?) and I suck at explaining things but I took the further organic option so let me just try first...

1.

water is a polar molecule because of the mickey mouse shape. you may be confused because CO2 (which has 2 atoms and one different one) is non polar while H2O (which also has 2 atoms and one different one) is polar. the reason is actually the structure. CO2 is linear (O=C=O), so the O=C and C=O vectors cancel each other, making the molecule non polar. but in H2O, it looks like the mickey mouse head so you see the one H-O bond is like to the northwest while the other O-H bond is like to the northeast so the vectors don't cancel each other and thus it's a polar molecule.

and then if you notice the Oxygen atom has 6 valence electrons, two of which are bonded to one H atom each while the other four are lone pair electrons. I think these lone pairs are the reason why water molecules attract positive...ions?

2.

tertiary halogenoalkanes have 3 methyl groups. you know that methyl groups increase the electron density? (it's been months since I learnt organic chem so if I'm wrong please correct me) I think it's the reason why it's easier to break the C-Halogen bond.

the more methyl groups there are, the more negative the molecule will be and hence it's easier for the Halogen atom to become a negative ion. because it's more negative. I think.

so then the rate determining step (the slow reaction) is faster than the reactions with secondary or primary halogenoalkanes (these have less methyl group, less electron density, more difficult to break the C-Halogen bond).

and then the C end becomes positive and will be attracted to the lone pair electrons.

keep in mind though I'm just taking SL and as I said I don't remember learning this before, but anyway I hope my explanation made sense. could you find something in your textbook to back up my ideas? if you find similar things then perhaps I explained it correctly!

Edited by Desy Glau
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The textbook states water is a weaker nucleophile than OH- because it lacks a negative charge,

Doubt 1- How is water a nucleophile in the first place when it has no charge?

A nucleophile's main requirement is that it has a lone pair of electrons.

Ammonia, water, amines, etc. are all nucleophiles.

It is this lone pair that is attracted to a region of positive (or partial positive) charge on an organic molecule.

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Guest KAPOWW!!

Re-posting:Doubt 2 'Water can react effectively with tertiary halogenoalkanes since the Sn1 reaction they undergo proceeds at a faster rate' can this be explained?

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