Below is one justified solution. In our “database‐driven” approach we note that detailed physicochemical numbers (for example, the topological polar surface area [tpsa], molecular weight, and calculated lipophilicity [xlogp]) differ in a systematic way when an oxazole ring bears a –CO2R group versus when it does not. In our PubChem “data” the ester derivatives (carboxylate-functionalized compounds) all show a tpsa of roughly 52 Å² (or higher when extra heteroatoms appear) and somewhat higher molecular weights (approximately 127–209 Da), whereas the non‐ester ligands show a tpsa of about 26–31 Å² with lower molecular weights and (often) lower rotatable‐bond counts. Furthermore, among the non‐esters the presence or absence of an aryl substituent produces additional differences in (for example) lipophilicity: non‐ester compounds with an appended phenyl (or a fused benzene as in benzoxazoles) show xlogp values on the order of 2–2.4 versus compounds with only alkyl‐type substituents that show values near 0.5–1.5.

On this quantitative basis we can classify the candidate substances into three groups:

––––––––––––––––––––––––––––––––––––––––––––––––––
Group 1: “Ester Oxazoles” (Carboxylate‐containing compounds) 
• These compounds all have a –CO2R (ester) group on the oxazole ring, which according to the data yields a higher tpsa (~52–80 Å²) and higher molecular weight.
 Examples (with representative data):
 – ethyl 5‑methyl‑1,2‐oxazole‑3‑carboxylate (MW ~155; tpsa ~52.3; xlogp ~1.4)
 – ethyl 1,2‐oxazole‑3‑carboxylate (MW ~141; tpsa ~52.3; xlogp ~0.9)
 – ethyl 5‑methyl‑1,2‐oxazole‑4‑carboxylate (MW ~155; xlogp ~1)
 – ethyl 1,2‐oxazole‑4‑carboxylate (MW ~141; xlogp ~0.6)
 – ethyl 3‑methyl‑1,2‐oxazole‑5‑carboxylate (MW ~155; xlogp ~1.3)
 – methyl 5‑(furan‑2‑yl)‑1,2‐oxazole‑3‑carboxylate (MW ~193; tpsa ~65.5; xlogp ~1.3)
 – methyl 5‑(thiophen-2-yl)‑1,2‐oxazole‑3‑carboxylate (MW ~209; tpsa ~80.6; xlogp ~1.9)
 – methyl 1,2‐oxazole‑5‑carboxylate (MW ~127; tpsa ~52.3; xlogp ~0.6)

––––––––––––––––––––––––––––––––––––––––––––––––––
Group 2: “Alkyl‐Substituted Non‐Ester Oxazoles”
• These have no carboxylate (ester) group and only carry small alkyl (or heterocyclic “alkyl‐like”) substituents. Their tpsa is low (≈26–31 Å²) and molecular weights are lower.
 Examples:
 – 3‑methyl‑1,2‑oxazole (MW ~83; tpsa ~26; xlogp ~0.8)
 – 3,5‑dimethyl‑1,2‑oxazole (MW ~97; tpsa ~26; xlogp ~1.2)
 – 5‑methyl‑1,2‑oxazole (MW ~83; tpsa ~26; xlogp ~0.5)
 – 5‑methyl‑3‑pyrrol-1-yl‑1,2‑oxazole (MW ~148; tpsa ~31; xlogp ~1.5)
  (the pyrrol-1-yl group, although heterocyclic, still counts as a “non‐aryl” aliphatic type substituent in this analysis)

––––––––––––––––––––––––––––––––––––––––––––––––––
Group 3: “Aryl‐Substituted Non‐Ester Oxazoles”
• These compounds bear one or more aryl groups (or have a benzoxazole ring system) appended to the oxazole. Their tpsa remains low (~26 Å²) but they are appreciably more lipophilic (xlogp around 2–2.4) and generally have higher molecular weights (in the range ca. 119–181 Da).
 Examples:
 – 3‑methyl‑5‑phenyl‑1,2‑oxazole (MW ~159; tpsa ~26; xlogp ~2.4)
 – 5‑(2,6‑difluorophenyl)‑1,2‑oxazole (MW ~181; tpsa ~26; xlogp ~2.2)
 – 4‑phenyl‑1,2‑oxazole (MW ~145; tpsa ~26; xlogp ~2)
 – 3‑phenyl‑1,2‑oxazole (MW ~145; tpsa ~26; xlogp ~2)
 – 5‑phenyl‑1,2‑oxazole (MW ~145; tpsa ~26; xlogp ~2)
 – 2,1‑benzoxazole (MW ~119; tpsa ~26; xlogp ~1.5)
 – 1,2‑benzoxazole (MW ~119; tpsa ~26; xlogp ~1.6)

––––––––––––––––––––––––––––––––––––––––––––––––––
Notes:
• Two candidate SMILES (the “C(N(Cc1ccccc1)c2ccon2)c3ccccc3” and “C(N(Cc1ccccc1)c2oncc2)c3ccccc3”) and the compound “ethyl 3-methoxy-1,2-oxazole-5-carboxylate” gave no PubChem record; thus, they are omitted from the grouping.
• The quantitative differences—especially the jump in tpsa from ~26 (non‐esters) to ~52+ (esters)—serve as our primary basis for the first (ester vs non‐ester) division, and the xlogp differences (near 2 for aryl‐substituted versus near 0.5–1.5 for simple alkyl derivatives) support a secondary division among the non‐ester structures.

This three‑group classification is entirely based on quantitative properties (e.g. tpsa, molecular weight, xlogp, and rotatable bond count) that one would expect to find in a comprehensive physicochemical property database.