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According to this paper, the deshielding effect of C=S group is specifically due to the delta(11), which is the least shielded component. However, the conclusion tells me that this component is governed by two transitions: σ → π(antibonding) and π → σ(antibonding) transition.

The thing confuses me is that, as the excited energy magnitude is smaller, the paramagnetic shielding should be more negative, also means the nucleus is more deshielded. When it comes to normal thought of C=O and C=S transtion, the n → π(antibonding) is lower in energy than σ → π(antibonding) and π → σ(antibonding). So why carbon on C=S has greater chemical shift than that of C=O?

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  • $\begingroup$ C=S being more deshielded could be due to the poor overlap between sulfur's 3p orbital with carbon's 2p orbital in comparison to the 2p-2p interaction in the C=O case, meaning the carbon on the C=S is more delta positive than the carbon on C=O. $\endgroup$
    – CurioChemo
    Mar 30 at 7:32
  • $\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$ Mar 30 at 7:33

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