Below is one way to classify these three candidate “base‐type” substances using a data‐driven approach. In a full physicochemical property database one would look at numbers such as the pKa of their conjugate acids (one of the most quantitative and commonly available measures of basicity), along with counts of available proton‐acceptor sites. For the purposes of this exercise, we assume that:

1. Acyclic amidine‐ or guanidine‐type bases (as in many common nitrogen‐bases) have conjugate acid pKa values typically in the 10–15 range. Quantitative database data (for example, measured conjugate acid pKa = 11–14) would support this.
2. Phosphazene–type bases (which feature P=N–linkages with highly electron‐rich nitrogen substituents) have very high conjugate acid pKa’s – often in the mid‐20s or higher (for example, pKa > 25).

Let’s briefly analyze the three supplied SMILES strings:

• Substance 1: “CN(C)/C(N(C)C)=N\\C(C)(C)C”
 – This structure shows an amidine/guanidine motif with N‐methyl groups and a bulky (t‑butyl–like) group on one end. In a quantitative database one would expect its conjugate acid pKa to fall in the moderate base range (roughly 11–14).

• Substance 2: “CN(C)P(N(C)C)(N(C)C)=NP(N(C)C)(N(C)C)=NCC”
 – In this structure the central atom is phosphorus and there are multiply N‐substituted P=N bonds. Phosphazene bases (which belong to this family) are known to have extremely high basicity (with conjugate acid pKa values in the mid‐20s or higher). Thus, quantitative data (for example, pKa ~30) would place this substance in a “superbase” category.

• Substance 3: “CN1CCCN2CCCN=C12”
 – This is a bicyclic guanidine-type system. Many bicyclic amidines/guanidines (such as DBU, DBN, or related compounds) show conjugate acid pKa values in the 11–14 range. A database lookup would be expected to provide numbers similar to substance 1.

Based solely on quantitative parameters (the conjugate acid pKa values being the key measurable property here), one can classify the candidates into two groups:
  Group A (“Moderate Nitrogen‐based Bases”): Substances 1 and 3, whose measured conjugate acid pKa values fall roughly between 10 and 15.
  Group B (“Phosphazene Superbase”): Substance 2, which has a much higher conjugate acid pKa (e.g., 25 or above).

Because we are allowed no more than three groups and because these three candidates do not spread out into more than two clearly distinct quantitative ranges, the quantitative evidence justifies partitioning the candidates into these two groups.

Thus, employing the quantitative “pKa‐of‐conjugate acid” criterion as the primary data we would conclude:

• Substances 1 and 3 (CN(C)/C(N(C)C)=N\C(C)(C)C and CN1CCCN2CCCN=C12) belong together as moderately basic compounds.
• Substance 2 (CN(C)P(N(C)C)(N(C)C)=NP(N(C)C)(N(C)C)=NCC) stands apart as a phosphazene superbase.

In summary, the three candidates can be classified in two groups based on their quantitative basicity data.