why sp2 hyb. have more e. density comp with sp3 in nmr calculation stuff ?
Because in a sp2 hyb., the bond is stronger, so atoms are closer then in sp3 single bond.
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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