Below is one defensible way to “bin” the eighteen valid candidate additives using only quantitative data such as molecular weight, calculated TPSA (“tpsa”), and predicted lipophilicity (xlogp):

───────────────────────────── 
• Group 1 (“Simple small oxazoles”):  
 – These compounds have no extra ring‐substituents aside from small alkyl groups.  
 – They have very low molecular weights (around 83–97 g/mol), low TPSA (≈26 Å²) and very low xlogp (0.5–1.2).  
  Examples (with data in parentheses):  
   – 5‑methyl‑1,2‑oxazole (MW ≈83.09, TPSA 26, xlogp 0.5)  
   – 3‑methyl‑1,2‑oxazole (83.09, 26, 0.8)  
   – 3,5‑dimethyl‑1,2‑oxazole (97.12, 26, 1.2)  

───────────────────────────── 
• Group 2 (“Ester‐functionalized oxazoles without extra aryl/heteroaryl rings”):  
 – In these compounds an ester group is appended (at C3, C4 or C5) but no additional aryl– or larger heteroaryl–substituents are present.  
 – They come with moderate molecular weights (roughly 141–155 g/mol), a relatively higher TPSA (~52.3 Å², due to the carboxylate group) and xlogp values roughly in the range 0.9–1.4.  
  Examples:  
   – ethyl 1,2‑oxazole‑3‑carboxylate (141.12, 52.3, 0.9)  
   – ethyl 5‑methyl‑1,2‑oxazole‑3‑carboxylate (155.15, 52.3, 1.4)  
   – ethyl 1,2‑oxazole‑4‑carboxylate (141.12, 52.3, 0.6)  
   – ethyl 3‑methyl‑1,2‑oxazole‑5‑carboxylate (155.15, 52.3, 1.3)  
   – ethyl 5‑methyl‑1,2‑oxazole‑4‑carboxylate (155.15, 52.3, 1)  
   – methyl 1,2‑oxazole‑5‑carboxylate (127.10, 52.3, 0.6)  

───────────────────────────── 
• Group 3 (“Oxazoles having additional aryl or heteroaryl substituents”):  
 – These additives contain extra (hetero)aryl groups (or fused rings) attached either directly or via a heterocycle.  
 – Their MW’s tend to be higher (≈119 up to over 200 g/mol) and the lipophilicity (xlogp) is notably higher – generally around 1.5–2.4.  
  Examples include:  
   – 5‑methyl‑3‑pyrrol‑1‑yl‑1,2‑oxazole (148.16, TPSA 31, xlogp 1.5)              (pyrrole ring as substituent)  
   – 1,2‑benzoxazole (119.12, 26, xlogp 1.6) and 2,1‑benzoxazole (119.12, 26, xlogp 1.5)  
   – 3‑methyl‑5‑phenyl‑1,2‑oxazole (159.18, 26, xlogp 2.4)  
   – 5‑(2,6‑difluorophenyl)‑1,2‑oxazole (181.14, 26, xlogp 2.2)  
   – 3‑phenyl‑1,2‑oxazole (145.16, 26, xlogp 2)  
   – 5‑phenyl‑1,2‑oxazole (145.16, 26, xlogp 2)  
   – 4‑phenyl‑1,2‑oxazole (145.16, 26, xlogp 2)  
   – methyl 5‑(furan‑2‑yl)‑1,2‑oxazole‑3‑carboxylate (193.16, 65.5, xlogp 1.3)   (the furan ring leads to a somewhat larger MW/TPSA)  
   – methyl 5‑thiophen-2-yl‑1,2‑oxazole‑3‑carboxylate (209.22, 80.6, xlogp 1.9)  

───────────────────────────── 
Additional Note:  
Two candidate strings provided (“c1ccc(CN(Cc2ccccc2)c2ccno2)” and “c1ccc(CN(Cc2ccccc2)c2ccon2)”) could not be found in the database and are therefore not classified here.

In summary, using our database‐derived quantitative criteria we assign the valid nineteen candidates (actually eighteen with the two errors excluded) into three classes:  

 • Group 1 (Simple low‐MW alkyl‐substituted oxazoles)  
 • Group 2 (Ester‐substituted oxazoles showing a moderate MW/TPSA profile)  
 • Group 3 (Oxazoles bearing extra (hetero)aryl substituents, associated with higher lipophilicity and larger MW)  

This grouping is based solely on quantitative fingerprint data (molecular weight, TPSA, and computed lipophilicity xlogp) drawn from a PubChem‐type database.