Why sp2 hyb. have more energy density compared with sp3?

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Discussion Overview

The discussion revolves around the comparison of sp2 and sp3 hybridization in terms of energy density and electron density, particularly in the context of NMR (Nuclear Magnetic Resonance) calculations. Participants explore the implications of hybridization on chemical shifts and shielding effects in NMR spectra.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the terminology used, asking whether "energy density" was meant instead of "electron density."
  • Another participant suggests that sp2 hybridization results in stronger bonds and closer atomic proximity compared to sp3, implying a relationship to energy density.
  • A participant notes that sp2 hybrids possess more s character than sp3 hybrids, which affects electron density near the nucleus and consequently influences shielding in NMR.
  • One reply points out that alkenes (sp2) are generally less shielded than alkanes (sp3) in NMR spectra, attributing this to the circulation of pi electrons in the magnetic field rather than a direct effect of electron density.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between hybridization, energy density, and shielding in NMR, indicating that the discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations regarding the definitions of energy density and electron density, as well as the assumptions about their implications in NMR calculations. The discussion does not resolve these ambiguities.

MrGenetic
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why sp2 hyb. have more e. density comp with sp3 in nmr calculation stuff ?
 
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Because in a sp2 hyb., the bond is stronger, so atoms are closer then in sp3 single bond.
 
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MrGenetic said:
why sp2 hyb. have more e. density comp with sp3 in nmr calculation stuff ?
Do you really mean energy density or rather electron density?

sp2 hybrids have more s character than sp3 hybrids. The chemical shifts depend on the electron density near the nucleus, but only s-orbitals have electron density at the nucleus, hence they are most effective in shielding.
 
This is kind of a weird question, given that alkenes are generally less shielded than alkanes, for both 1H and 13C NMR spectra. However, this is due to the circulation of the pi electrons induced by the applied magnetic field, not any effect having to do directly with electron density.
 
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