Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: a student on May 28, 2010, 01:58:28 AM
-
hi
I have searched about B-N single bond in internet but I didn't find anything about that :o now I feel that may be it doesn't exist at all am I right? is there anything wrong with that bond? if there is I would be gratefull to help me :P
-
Just think if pure single bond between B and N is possible at all. Trivalent boron is electron deficient, nitrogen is electron rich.
But BF3-NH3 with dative bond exists.
-
Just think if pure single bond between B and N is possible at all. Trivalent boron is electron deficient, nitrogen is electron rich.
thanks for your reply I mean something like this:
-
But your compound contains single+dative bond ie ~double bond
-
Much research has been conducted on aminoboranes. Look at this paper and the references in it:
J. Org. Chem. 2009, 74, 1964.
-
But BF3-NH3 with dative bond exists
But surely a dative bond is still a single bond. The word 'dative' is simply an accounting term to show that both electrons originated from the same atom and explain why they are relatively unstable.
A hydrogen bond, for instance, is clearly different to a conventional bond because it has much less electron density and longer bond lengths but I'm not aware of any similar differences between conventional covalent bonds and dative bonds. In molecular orbital theory, both are surely equivalent. If there are any significant differences, I would love to hear.
-
But surely a dative bond is still a single bond. The word 'dative' is simply an accounting term to show that both electrons originated from the same atom and explain why they are relatively unstable.
True. Dative/co-ordinate bonds are called so because of the origin of the bonding electrons. Once the bond is formed, it is indistinguishable from the 'traditional' covalent bond.
Dative bonds are not new kinds of bonds.
-
Really?
add strong acid into ethane and into Ag(NH3)2Cl solution ?
-
@AWK : Sorry, but can you please explain what happens in both cases? Is it an example that can help distinguish the two bonds?
-
In the first case - nothing
2.
Ag(NH3)2Cl + 2HNO3 = AgCl + 2NH4NO3
Most dative bonds (but not all) are weaker then covalent ones.
-
I still don't get it AWK. How does that reaction prove that Most dative bonds (but not all) are weaker then covalent ones?
-
g(NH3)2Cl + 2HNO3 = AgCl + 2NH4NO3
So, by protonating ammonia to ammonium, ammonium will be eliminated from the complex. It's hardly surprising that ammonium has different binding properties to ammonia but I don't see how that is a property that is unique to a 'dative' bond. You can also eliminate H2O from ethanol by protonating OH to form water. I don't see the fundamental difference.
As far as I can see, the concept of dative bonds are useful for accounting purposes and for predicting good leaving groups but the bonds themselves are fundamentally the same. If someone can give an orbital description or similar to explain the difference I'd be happy to hear about it.
Significantly, none of my three textbooks on inorganic chemistry even carry the term 'dative bond' in the index.
-
So, by protonating ammonia to ammonium, ammonium will be eliminated from the complex. It's hardly surprising that ammonium has different binding properties to ammonia but I don't see how that is a property that is unique to a 'dative' bond. You can also eliminate H2O from ethanol by protonating OH to form water. I don't see the fundamental difference.
My point exactly. That reaction just stresses upon the difference in bonding properties of ammonia and ammonium, which is, as demoninatutu rightly said, hardly surprising. It has nothing to do with strength of dative bonds vs strength of covalent bonds right?
Or am I wrong?
-
The only way you will be able to tell is by looking at the energy for homolytic bond cleavage.