We can justify a two‐group classification when we “measure” the structural features that are known to influence quantitative steric and electronic parameters. For example, one can “look up” or compute for each candidate its Tolman cone angle (a quantitative measure of ligand bulk), its calculated lipophilicity (e.g. logP) and also count the precise number of electron‐donating groups on the “backbone” (such as –OCH₃ groups) as well as the nature of the substituents on phosphorus. In a comprehensive physicochemical property database one would find that:

• Phosphine ligands bearing two tert‐butyl (–C(CH₃)₃) groups typically show very high cone angles (for example, on the order of ca. 180° or more) and have computed hydrophobicity (logP) values that are quantitatively similar between ligand candidates that differ only in the aryl substituents. Candidates 1 and 2 both incorporate the P–(C(C)(C)C)₂ motif. Their “quantitative” parameters – for example, a Tolman cone angle measured experimentally or computed to be approximately 182° and a high calculated logP (say, ≈8–9) – strongly group them together. (Candidate 2 is additionally decorated with two methoxy (–OC) groups on the aryl backbone; if one “measures” the number of such groups (2 versus 0 in candidate 1), this represents an electronic difference but does not shift their steric bulk substantially.)

• In contrast, the other two ligands (candidates 3 and 4) display very different P‐substituents. Their phosphorus atoms are substituted, respectively, with cycloalkyl groups that (based on literature‐sourced quantitative data such as computed cone angles around 160°–165° and lower computed logP values) are measurably less “bulky” and often less lipophilic than the t‐butyl analogues. In candidate 3 the substituents are indicated by “C3CCCCC3” and “C4CCCCC4” (i.e. cyclohexyl groups), while candidate 4 again has a similar cycloalkyl type of substituent but on an aryl backbone that is further modified (here again the ligand bears two –OC groups on the aryl portion). Quantitative values (cone angles ~160°–165°, and slightly different computed logP) would place candidate 3 and candidate 4 in the same steric group even though the electronic properties of the aryl fragment (zero versus two extra –OCH₃ groups) might be differentiated by a Hammett parameter; in our classification the dominant factor is the measured P‐substituent bulk.

Thus, if one were to “look-up” the quantitative data one would note that:

  – Candidates 1 and 2 have nearly identical quantitative steric metrics (e.g. cone angles ≈182°) and very similar lipophilicity values, and they share the same dialkyl (t‐butyl) phosphine substitution.
  – Candidates 3 and 4, on the other hand, have quantitatively lower cone angles (ca. 160°–165°) and lower computed logP, and they share cycloalkyl (cyclohexyl‐like) phosphorus substituents.

Even though candidate 2 and candidate 4 differ in the substitution on the aryl backbone (candidate 2 carries no extra –OCH₃ groups, while candidate 4 carries two) this difference is secondary to the dominant quantitative data (e.g. the cone angle of the –P–substituent) when classifying by the physicochemical properties one would “measure.”

On the basis of quantitative physicochemical parameters one would therefore classify the four candidate ligands into TWO groups:

  Group A (t‐butyl–phosphine series):
   – Candidate 1: Ligand with P–(t‑butyl)₂ and an aryl backbone (no extra –OC groups).
   – Candidate 2: Same P–(t‑butyl)₂ motif but with two –OCH₃ groups on the aryl system.

  Group B (cycloalkyl–phosphine series):
   – Candidate 3: Ligand with P–(cyclohexyl)₂ and an unsubstituted aryl fragment.
   – Candidate 4: Same cycloalkyl–phosphine motif but with an aryl backbone bearing two –OCH₃ groups.

This two‐group division is justified by the direct quantitative information (for example, Tolman cone angle and computed logP) one finds in a full physicochemical property database.