head-tail isomerism

synonyms: HT-isomerism, regioisomerism
https://doi.org/10.1351/goldbook.08824
Constitutional isomerism of polymeric (oligomeric) chains composed of identical non symmetric repeating units consisting in different orientations of the units.
Notes:
  1. In the repeating unit of a vinyl polymer: −CHR−CHA2−, the substituent-bearing group CHR is denoted 'head' (H) while the other one 'tail' (T). There exist three modes how two such units can be linked in a chain: head-to-tail (HT), head-to-head (HH) and tail-to-tail (TT).
  2. The uniformity/non-uniformity of repeating units’ orientation determines the regularity/irregularity of macromolecules.
See also: regioregular polymer
Source:
PAC, 2022, 94, 15. (Glossary of terms relating to electronic, photonic and magnetic properties of polymers (IUPAC Recommendations 2021)) on page 34 [Terms] [Paper]
Citation: 'head-tail isomerism' 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.08824 RIS BibTex EndNote
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