We can “quantitatively‐group” these three very similar trifluoromethyl‐substituted benzenes by focusing on measured properties that differ appreciably between them—in this case, largely the molecular (exact) weight and the corresponding “exact_mass” value, which differ as a direct consequence of using a different halogen at the para‐position. (Other properties such as the number of accepted hydrogen bonds, heavy atom count, tPSA, and even the calculated logP [xlogp] are nearly identical.)

For example, from the PubChem data:
 • 1‐chloro‑4‑(trifluoromethyl)benzene: exact_mass ≈ 179.995 and molecular_weight ≈ 180.55  
 • 1‐bromo‑4‑(trifluoromethyl)benzene: exact_mass ≈ 223.945 and molecular_weight ≈ 225.01  
 • 1‑iodo‑4‑(trifluoromethyl)benzene: exact_mass ≈ 271.931 and molecular_weight ≈ 272.01

These quantitative differences are significant and directly reflect the identity of the halogen substituent. (The xlogp values vary only slightly—3.8 vs. 3.9 vs. 3.6—so they confirm overall similar lipophilicity rather than drive a grouping.)

Thus, using our quantitative “database‐like” criteria the substances can be classified into three groups:
 • Group 1 ("Chloro class"): 1‑chloro‑4‑(trifluoromethyl)benzene  
 • Group 2 ("Bromo class"): 1‑bromo‑4‑(trifluoromethyl)benzene  
 • Group 3 ("Iodo class"): 1‑iodo‑4‑(trifluoromethyl)benzene

Because the only major quantitative difference among these candidates is the identity (and resulting mass) of the halogen, we use the exact molecular weight as the primary classifier. This quantitative distinction justifies placing the three substances into three separate groups rather than lumping them all together in one class.