preferred constitutional repeating unit

initialism: P-CRU
https://doi.org/10.1351/goldbook.09016
Constitutional repeating unit (CRU) written with the subunits in a linear series from the highest (higher) seniority to the lowest (lower) or as close as possible by the shortest path.
Notes:
  1. This definition is based on descriptions of methods to reach the P-CRU.
  2. The P-CRU is chosen with the lowest possible locant(s) for the substituents.
Examples:
  1. \(\ce{-[O-CH2CH2-S-CH2CH2]_{n}\bond{-}}\ \rm{not}\ \ce{-[S-CH2CH2-O-CH2CH2]_{n}\bond{-}}\)
  2. \(\ce{-[O-CH2CH2-O-CH2CH2CH2]_{n}\bond{-}}\ \rm{not}\ \ce{-[O-CH2CH2CH2-O-CH2CH2]_{n}\bond{-}}\)
Source:
PAC, 2021, 93, 963. (Structure-based nomenclature for irregular linear, star, comb, and brush polymers (IUPAC Recommendations 2020)) on page 966 [Terms] [Paper]
Citation: 'preferred constitutional repeating unit' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.09016 RIS BibTex EndNote
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