senior constitutional repeating unit

initialism: S-CRU
https://doi.org/10.1351/goldbook.09015
More (most) senior CRU of a structure of a macromolecule or oligomer molecule containing two or more different types of CRUs.
Notes:
  1. The CRU beginning with the subunit of highest (higher) seniority is chosen as the S-CRU.
  2. If CRUs begin with an identical subunit, the choice depends on the seniority of the remaining subunits and the number and position of substituents.
Examples:
  1. −[O−CHA2CHA2]An− not −[N−CHA2CHA2]An−
  2. −[O−COCHA2]An− not −[O−CHA2CHA2]An−
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: 'senior 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.09015 RIS BibTex EndNote
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