Inductive Effects in NBO

Inductive Effects in NBO

Postby thechronosphere » Fri Jan 30, 2015 10:06 am

Hello,

I have a simple question for you. I believe that finding the answer to this question will aid me in interpreting NBO results better.

Is it possible to demonstrate the presence of inductive effects via NBO results?
For example, in the case of benzaldehyde, where the presence of formyl group is known to have an electron withdrawing effect due to two reasons: inductive effects and mesomeric effects.
Is it possible to "somehow" quantify the magnitude of these two effects and compare them?
I think that by looking at the charge transfer between a pi bond NBO on the ring and pi bond NBO of C=O in benzaldehyde, one can understand mesomeric effect (in 2nd order perturbation analysis results part). But in order to fully understand the inductive effect due to the addition of a formyl group to a phenyl ring, which interactions should one look at?

Thanks for your advice in advance.
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Re: Inductive Effects in NBO

Postby ericg » Sun Feb 01, 2015 1:11 pm

Molecules like benzaldehyde reveal evidence of inductive effects, although the extent of these effects cannot be quantified energetically as with the perturbative analysis of resonance effects. Inductive effects in the benzene ring of benzaldehyde are seen in the polarization of the CC sigma bonds toward the ipso carbon.

Eric
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Re: Inductive Effects in NBO

Postby thechronosphere » Wed Feb 25, 2015 8:01 am

Thank you for the response, I have also seen polarization of the CC sigma bond as well. I have thought about what other things could be done to demonstrate this effect (via NBO results) and the only thing that I could find is to look at the natural atomic charges of the atoms that are closest to oxygen in benzaldehyde which is expected to have a inductive charge interaction with the lone pair on oxygen.

I would like to understand the importance of mesomeric effects due to the presence of substituents on a phenyl ring and quantify them. For instance, in a double substituted benzene, presence of an electron withdrawing group and electron donating group in -o or -p positions leads to stabilization of the molecule due to mesomeric effects. Such interactions can clearly be seen in the list of stabilization energies of NBO interactions. Is it possible to use stabilization energies to quantify the effect of resonance occuring due to presence of these substituent groups and distinguish these effects from the resonance due to aromaticity of the phenyl ring?
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