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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Winga on November 24, 2004, 11:53:34 PM

Title: About the bonds of SO3!
Post by: Winga on November 24, 2004, 11:53:34 PM
Some books said SO3 has three S=O double bonds; some said it has three S-O dative covalent bonds; and some said it has two S=O double bonds & one S-O dative covalent bond.

Which one is correct?  
Title: Re:About the bonds of SO3!
Post by: AWK on November 25, 2004, 01:59:41 AM
Sulfur belongs to the third period and for it the octet rule should not be fulfilled,
but formally it is fulfilled in the case of one double bond and two dative covalent bonds.
As a teacher I prefer this method, and accept three double bonds, but not the other possibilities presented by you.
The octet rule is absolutely required for the second period.
Title: Re:About the bonds of SO3!
Post by: Winga on November 25, 2004, 07:11:10 AM
How about drawing the mechanism of sulfonation of benzene?

I saw the book, whcih using 3 S=O double bonds. So, can I draw the mechanism by using one double bond and two dative covalent bonds?
Title: Re:About the bonds of SO3!
Post by: Donaldson Tan on November 25, 2004, 05:30:25 PM
actually, in virtue of electron delocalisation, all three structures suggested are actually cannonical structures. SO3 exhibits reasonance, whereby its actual structure is in between these 3. ie. the bond order each S-O bond is actually 1.5.
Title: Re:About the bonds of SO3!
Post by: Mitch on November 25, 2004, 08:50:34 PM
you mean 1.666?
Title: Re:About the bonds of SO3!
Post by: AWK on November 26, 2004, 01:08:25 AM
Draw the mechanism according to scheme of electrophilic aromatic substitution:
1. pi-complex
2. sigma complex
3. H(+) shift
Title: Re:About the bonds of SO3!
Post by: Winga on November 26, 2004, 02:16:39 AM
Quote from: Mitch on November 25, 2004, 08:50:34 PM
you mean 1.666?
Is it 6 e- shared by 4 atoms? 1.5?
Title: Re:About the bonds of SO3!
Post by: Donaldson Tan on November 26, 2004, 11:46:39 AM
what exact number is the bond order does not matter. what matters is that sulphur-oxygen bond is somewhat between a single and double bond because of electron delocolisation. the delocalised electrons move readily within the adjacent degenerate molecular orbitals.