Structural element

Structural elements marked in blue in the structural formulas of three polymers: polyethylene (top), polypropylene (middle) and polyethylene terephthalate (PET, bottom).

In chemistry, a structural element (also called a structural fragment) is a characteristic part of the structural formula of a larger molecule .

In a polymer , the smallest repeating grouping is called the structural element. The structural element can be smaller, the same size or larger than a basic module.

• Example:
  • In polyethylene , the monomer ethene forms the basic building block for the grouping (–CH ₂ = CH ₂ -) and the structural element is a methylene group (–CH ₂ -).
  • In polypropylene , the monomer propene is the basic building block of the grouping (-CH ₂ = CH (CH ₃ )) - and the structural element is the double-bonded grouping -CH ₂ = CH (CH ₃ ) -.
  • in polyethylene terephthalate (PET), ethylene glycol and terephthalic acid are the monomers. The basic building blocks are the –O – CH ₂ –CH ₂ –O– groups and the double-bonded diacyl radical of terephthalic acid.

Individual evidence

1. ^ Siegfried Hauptmann : Organic Chemistry , 2nd edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig 1985, p. 723, ISBN 3-342-00280-8 .