Are double bonds/resonance structures more nucleophilic?

  • Thread starter Simfish
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  • #1
Simfish
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I'm only talking about carbon-carbon double/triple bonds here.

A nucleophilic atom is one that would donate electrons to an electrophile (often a highly electronegative atom like oxygen or a halogen). Anyways, what about carbon-carbon double bonds? I'm inclined to think that they're less nucleophilic since their formal chage is reduced by the double bond (so there are fewer electrons to go around each carbon atom).

Does the same logic apply to resonance structures in benzene rings?
 

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  • #2
chemisttree
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I'm only talking about carbon-carbon double/triple bonds here.

A nucleophilic atom is one that would donate electrons to an electrophile (often a highly electronegative atom like oxygen or a halogen). Anyways, what about carbon-carbon double bonds? I'm inclined to think that they're less nucleophilic since their formal chage is reduced by the double bond (so there are fewer electrons to go around each carbon atom).

Does the same logic apply to resonance structures in benzene rings?
More nucleophilic than what? Double bonds do donate their electrons in reactions so in that sense they are nucleophilic. They tend to do it to strong acids, specifically the proton. Usually the first step addition with HX. With benzene structures, strong acids like you would find in Friedel-Crafts conditions can be thought of in this way.

Triple bonds are a special case.
 
  • #3
Simfish
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Are they more nucleophilic than carbon-carbon single bonds?

Oh okay I see. Could double bonds also be electrophilic? (with respect to strong nucleophiles?)
 
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It's hard to give a definitive answer to this because it depends on a lot of things, e.g. what double bond/triple bond is reacting with and what its substituents are. With a strong enough electrophile, a double bond will be nucleophilic. Similarly, with a strong enough nucleophile, a double bond will be electrophilic.

In general though, double bonds that have an electrophilic substituent, e.g. something like C=C-NO2, will be electrophilic at the beta carbon, and something CH3S- can add to the double bond.
 

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