### Step 1: Compiling and Summarizing Physicochemical Data

From your provided database output for each ligand, the following **quantitative physicochemical properties** are available and relevant for classification:

- **Molecular Weight**
- **Molecular Formula**
- **XLogP (Predicted logP, a measure of hydrophobicity)**
- **TPSA (Topological Polar Surface Area)**
- **H-Bond Donor Count**
- **H-Bond Acceptor Count**
- **Rotatable Bond Count**

Below is a summary table for all four ligands:

| Ligand Short Name                                           | Mol. Wt. | XLogP | TPSA | H-Bond Donor | H-Bond Acceptor | Rot. Bonds |
|-------------------------------------------------------------|----------|-------|------|--------------|-----------------|------------|
| ditert-butyl-triisopropylphenyl-phenyl-phosphane            | 424.6    | 8.5   | 0    | 0            | 0               | 7          |
| ditert-butyl-dimethoxy-triisopropylphenyl-phenyl-phosphane  | 484.7    | 8.4   | 18.5 | 0            | 2               | 9          |
| dicyclohexyl-triisopropylphenyl-phenyl-phosphane            | 476.7    | 10.1  | 0    | 0            | 0               | 7          |
| bis(1-adamantyl)-dimethoxy-triisopropylphenyl-phenyl-phos.  | 640.9    | 11.8  | 18.5 | 0            | 2               | 9          |


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### Step 2: Identifying Discriminating Quantitative Properties

#### **1. XLogP (Hydrophobicity)**
- 8.4–8.5: ditert-butyl variants (regardless of methoxy groups)
- 10.1: dicyclohexyl variant
- 11.8: bis(adamantyl) variant

#### **2. TPSA (Polarity)**
- 0: All ligands *without* methoxy groups (ditert-butyl-triisopropyl and dicyclohexyl-triisopropyl)
- 18.5: All ligands *with* methoxy groups (ditert-butyl-dimethoxy and bis(adamantyl)-dimethoxy)

#### **3. H-Bond Acceptors**
- 0: Those without methoxy groups
- 2: Those with methoxy groups

#### **4. H-Bond Donors**
- 0 for all ligands

#### **5. Molecular Weight**
- <500: all except bis(adamantyl)
- >600: bis(adamantyl)-dimethoxy

---

### Step 3: Classification Scheme

#### **A. By Polarity (TPSA/H-Bond Acceptors)**
- Group 1: "Non-polar" — TPSA = 0, H-bond acceptor = 0
  - ditert-butyl-triisopropylphenyl-phenyl-phosphane
  - dicyclohexyl-triisopropylphenyl-phenyl-phosphane
- Group 2: "Polarized" — TPSA = 18.5, H-bond acceptor = 2
  - ditert-butyl-dimethoxy-triisopropylphenyl-phenyl-phosphane
  - bis(1-adamantyl)-dimethoxy-triisopropylphenyl-phenyl-phosphane

#### **B. By Hydrophobicity (XLogP)**
- Group 1: XLogP 8–8.5 (Moderate hydrophobic)
  - Both ditert-butyl ligands (regardless of methoxy)
- Group 2: XLogP 10–12 (High hydrophobic)
  - dicyclohexyl and bis(adamantyl) ligands

But this would split the dimethoxy ligands and group molecules that are different in terms of polarity.

#### **C. By Bulk/Steric Hindrance (Mol. Wt., Rot. Bonds)**
- Group 1: <500 Da ("Regular bulk")
  - ditert-butyl ligands and dicyclohexyl ligand
- Group 2: >600 Da ("High bulk")
  - bis(1-adamantyl)-dimethoxy

As only one ligand falls above this threshold, this division is less useful unless forced to distinguish steric classes.

---

### Step 4: Selecting a Justifiable Classification

**TPSA and H-bond acceptor count provide a clear, database-justified split according to the presence/absence of methoxy groups.**  
**Hydrophobicity (XLogP) is less discriminative unless using three groups, but the split isn’t as clear-cut as with TPSA.**

### **FINAL CLASSIFICATION**

#### **Group 1: Non-polar, no significant H-bond accepting capability**  
- ditert-butyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane  
  - (TPSA=0, H-bond acceptor=0)  
- dicyclohexyl-[2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane  
  - (TPSA=0, H-bond acceptor=0)  

#### **Group 2: Polarized, significant H-bond acceptance due to methoxy groups**  
- ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane  
  - (TPSA=18.5, H-bond acceptor=2)  
- bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(propan-2-yl)phenyl]phenyl]phosphane  
  - (TPSA=18.5, H-bond acceptor=2)  

**Justification:**  
- This division is entirely supported by TPSA (a direct database number) and H-bond acceptor count (another direct database number), both of which are standard measurable indices of polarity and hydrogen bonding ability.
- These two categories also correspond to presence/absence of electron-donating methoxy groups, providing a rational property-based split.

---

### **Summary Table of Final Classes**

| Ligand Short Name                | CLASS      | TPSA | H-bond acceptor |
|----------------------------------|------------|------|-----------------|
| ditert-butyl-triisopropyl        | Non-polar  | 0    | 0               |
| dicyclohexyl-triisopropyl        | Non-polar  | 0    | 0               |
| ditert-butyl-dimethoxy           | Polarized  | 18.5 | 2               |
| bis(adamantyl)-dimethoxy         | Polarized  | 18.5 | 2               |

---

## **No More Than Three Groups Were Used, All Decisions Were Based on Quantitative Database Values.**  
If you need, I can provide alternative groupings (by logP, by molecular weight) or further discuss ambiguous cases.