Editing Tacticity (section)

===Diads===
Two adjacent structural units in a polymer molecule constitute a '''diad'''. Diads overlap: each structural unit is considered part of two diads, one diad with each neighbor. If a diad consists of two identically oriented units, the diad is called an '''{{nobr|m diad}}''' (formerly ''meso diad'', as in a [[meso compound]], now proscribed<ref name="danrotp">{{cite journal|title=Definitions and notations relating to tactic polymers (IUPAC Recommendations 2020)|journal=[[Pure and Applied Chemistry]]|year=2020|volume=92|issue=11|pages=1769–1779|doi=10.1515/pac-2019-0409|url=https://www.degruyter.com/document/doi/10.1515/pac-2019-0409/html|last1=Fellows|first1=Christopher M.|last2=Hellwich|first2=Karl-Heinz|last3=Meille|first3=Stefano V.|last4=Moad|first4=Graeme|last5=Nakano|first5=Tamaki|last6=Vert|first6=Michel|hdl=11311/1163218|hdl-access=free}}</ref>).  If a diad consists of units oriented in opposition, the diad is called an '''{{nobr|r diad}}''' (formerly ''racemo diad'', as in a racemic compound, now proscribed<ref name="danrotp" />).  In the case of vinyl polymer molecules, an {{nobr|m diad}} is one in which the substituents are oriented on the same side of the polymer backbone; in the Natta projection, they both point into the plane or both point out of the plane.