(1) The Huynh Electronic Parameter (HEP) is known to measure the σ-donation ability of classical Werner-type ligands, such as NHCs and related C-donor ligands. It is therefore expected to be similar to the 1 JC-H coupling constant. However, the comparison between experimental HEP and 1 JC-H measurements is limited by the lack of data. Furthermore, the solvent and counterion used to measure 1 JC-H are not always the same, while HEP is consistently measured in CDCl3, which can slightly distort the comparison. To eliminate any potential bias, we have calculated the 1 JC-H coupling constant in CDCl3 for 42 NHCs with known HEP values. Figure highlights significant discrepancies between HEP and 1 JC-H values, with no significant relationship found between the two (R 2 =0.25). Moreover, the data points tend to cluster according to carbene classes (Figure ), highlighting distinct trends and variations within specific carbene families. This clustering indicates that JC-H values are less influenced by substituents compared to HEP. For instance, the range of A careful examination of Figure suggests that 1 JC-H is particularly sensitive to two parameters: the nature of the atoms bonded to the carbenic carbon atom, and the Y-Ccarbene-Y angle.