Meaning of the numbers in nylon-66: what do the first and second “6” designate?

Introduction / Context:
Nylon nomenclature encodes the number of carbons in the monomers. Understanding this quickly identifies raw materials and links structure to thermal and mechanical properties.

Given Data / Assumptions:

• Nylon-66 is a condensation polyamide.
• Two integers refer to diamine and diacid, respectively.
• Monomers are standard industrial chemicals.

Concept / Approach:
In nylon-66, the first 6 corresponds to the 6-carbon diamine (hexamethylene diamine), and the second 6 to the 6-carbon diacid (adipic acid). The polymer results from amide formation between these monomers. Options that involve “rings” are distractors; nylon-66 is aliphatic.

Step-by-Step Solution:
Recall naming rule: first number = carbons in diamine; second number = carbons in diacid.Apply to nylon-66: HMD (6) + adipic acid (6).Select the matching option.

Verification / Alternative check:
Nylon family naming (e.g., nylon-6,10; nylon-11) follows the same convention, confirming the interpretation.

Why Other Options Are Wrong:
References to aromatic rings do not apply to nylon-66.“None of these” is invalid because a correct mapping exists.

Common Pitfalls:
Confusing nylon-6 (from caprolactam) with nylon-66 (from two monomers).

Final Answer:
Hexamethylene diamine and adipic acid (each has 6 carbons).