To classify these candidate substances **using only quantitative physicochemical property data** from the provided database, we must first **summarize the relevant properties** that can be consistently extracted and compared. The most widely and consistently available quantitative properties are:

## Quantitative Physicochemical Properties (Extracted):

1. **XLogP (octanol–water partition coefficient, logP):** Proxy for hydrophobicity/hydrophilicity (polarity).
2. **TPSA (Topological Polar Surface Area, Å²):** Proxy for polarity and potential for hydrogen bonding.
3. **H-bond acceptor count:** Proxy for electron-withdrawing groups, polarity, solubility.
4. **Molecular Weight:** Sometimes used for volatility/size classes.
5. **Rotatable bond count:** Proxy for molecular flexibility, but less relevant here.
6. **Presence/absence of carboxyl or ester groups (can be inferred from formula/smiles and h-bond acceptors/TPSA):** Strongly increases polarity/TPSA.

Other properties (e.g., pKa, dielectric constant, boiling point) **are not provided**.

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## Categorization Plan

Given the data, the **most distinguishing quantitative features** are:
- **TPSA** (and Y/N for ester group)
- **Number of H-bond acceptors** (as aux feature)
- **XLogP**

**Thresholds** for classes are derived from literature and the spread in the data.
- **TPSA ~26** (no ester/carboxyl, just oxazole core)
- **TPSA ~52.3–80.6+** (esters or more polar functional groups)
- **XLogP:**
   - Low/Negative: Highly polar
   - ~0–1.5: Moderately polar
   - >1.5: Increasing hydrophobicity

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### **Step 1: Examine major breaks/trends**

**Set 1: "Core" oxazole compounds (unsubstituted, simple substitution)**  
- TPSA = 26
- H-bond acceptor = 2
- No carboxylate/ester group
- XLogP ≈ 0.5–2.4 (modestly hydrophobic; mostly aromatic/alkyl/aryl substitution)

**Set 2: "Ester/carboxyl-modified" oxazoles**  
- TPSA = 52.3–80.6+
- H-bond acceptor = 4 or 5
- All have -COOEt/-COOMe groups
- XLogP can be slightly hydrophilic to up to ~2

**Exceptions:**
- Pyrrole/furan/thiophene/fluoro-phenyl substituents increase H-bond acceptor count/TPSA a little
- Substituted benzo/phenyl-like groups don't strongly change TPSA or acceptor count
- Two SMILES without database values (cannot classify: "no compound found")

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## **Final Grouping (NO MORE THAN 3 GROUPS)**

**Group 1: "Core/Nonpolar to Moderately Polar Oxazoles"**  
(*TPSA = 26, H-bond acceptor = 2, no carboxyl/ester, XLogP 0.5–2.4*)
- 1,2-benzoxazole
- 2,1-benzoxazole
- 3,5-dimethyl-1,2-oxazole
- 3-methyl-1,2-oxazole
- 3-methyl-5-phenyl-1,2-oxazole
- 3-phenyl-1,2-oxazole
- 4-phenyl-1,2-oxazole
- 5-(2,6-difluorophenyl)-1,2-oxazole  (TPSA 26, but H-bond acceptor = 4 due to F, but core same, so clusters here)
- 5-methyl-1,2-oxazole
- 5-methyl-3-pyrrol-1-yl-1,2-oxazole (TPSA = 31; slightly higher, but fits better here)
- 5-phenyl-1,2-oxazole

**Group 2: "Ester/Highly Polar Oxazoles"**  
(*TPSA ≥ 52.3, H-bond acceptor = 4–5, XLogP up to ~2, clear carboxylate/ester functional group presence*)
- ethyl 1,2-oxazole-3-carboxylate
- ethyl 1,2-oxazole-4-carboxylate
- ethyl 3-methyl-1,2-oxazole-5-carboxylate
- ethyl 5-methyl-1,2-oxazole-3-carboxylate
- ethyl 5-methyl-1,2-oxazole-4-carboxylate
- methyl 1,2-oxazole-5-carboxylate
- methyl 5-(furan-2-yl)-1,2-oxazole-3-carboxylate (TPSA 65.5; H-bond acceptor 5)
- methyl 5-thiophen-2-yl-1,2-oxazole-3-carboxylate (TPSA 80.6; H-bond acceptor 5)

**Group 3: "No Data—Unable to Group"**  
- c1ccc(CN(Cc2ccccc2)c2ccno2)cc1  
- c1ccc(CN(Cc2ccccc2)c2ccon2)cc1  
- ethyl 3-methoxy-1,2-oxazole-5-carboxylate  
(*Class membership indeterminable due to lack of property data.*)

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## **Justification & Summary Table (Sample)**

| Substance                                    | TPSA   | XLogP | H-bond acceptor | Group           |
|-----------------------------------------------|--------|-------|-----------------|-----------------|
| 1,2-benzoxazole                              | 26     | 1.6   | 2               | Group 1         |
| 3,5-dimethyl-1,2-oxazole                     | 26     | 1.2   | 2               | Group 1         |
| 3-phenyl-1,2-oxazole                         | 26     | 2.0   | 2               | Group 1         |
| 5-methyl-1,2-oxazole                         | 26     | 0.5   | 2               | Group 1         |
| ethyl 1,2-oxazole-3-carboxylate              | 52.3   | 0.9   | 4               | Group 2         |
| ethyl 3-methyl-1,2-oxazole-5-carboxylate     | 52.3   | 1.3   | 4               | Group 2         |
| methyl 5-(furan-2-yl)-1,2-oxazole-3-carboxylate | 65.5 | 1.3   | 5               | Group 2         |
| methyl 5-thiophen-2-yl-1,2-oxazole-3-carboxylate | 80.6 | 1.9   | 5               | Group 2         |
| [No Data: c1ccc(CN(Cc2ccccc2)c2ccno2)cc1 ]   |   -    |  -    |  -              | Group 3         |

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### **Conclusion**
**Quantitative data (TPSA, H-bond acceptors, functional group presence) produce two clear main classes**, with a third for entries lacking property data.
- **Group 1:** Core oxazoles, modest polarity, no carboxylate/ester, TPSA = 26 (± small margin)
- **Group 2:** Ester/carboxyl-modified, higher polarity, higher TPSA (≥52.3)
- **Group 3:** Indeterminate (no database values)

**All compounds could be so classified by TPSA and functional group presence, based strictly on quantitative data—meeting the instruction to minimize reliance on unquantified intuition.**

If you require an actual listing or table for all compounds, I can generate it for you. If you need further grouping refinement, specify another property or category.