Editing Tacticity (section)

===Triads===

The stereochemistry of macromolecules can be defined even more precisely with the introduction of triads.  An '''isotactic triad''' (''mm'') is made up of two adjacent m diads, a '''syndiotactic triad'''  (also spelled '''syndyotactic'''<ref>Webster's Third New International Dictionary of the English Language, Unabridged; Oxford English Dictionary.</ref>) (''rr'') consists of two adjacent {{nobr|r diads}}, and a '''heterotactic triad''' (''rm'') is composed of an {{nobr|r diad}} adjacent to an {{nobr|m diad}}.  The mass fraction of isotactic (''mm'') triads is a common quantitative measure of tacticity.

When the stereochemistry of a macromolecule is considered to be a [[Bernoulli process]], the triad composition can be calculated from the probability ''P''<sub>m</sub> of a diad being {{nobr|m type}}. For example, when this probability is 0.25 then the probability of finding:
*an isotactic triad is ''P''<sub>m</sub><sup>2</sup>, or 0.0625
*an heterotactic triad is 2''P''<sub>m</sub>(1–''P''<sub>m</sub>), or 0.375
*a syndiotactic triad is (1–''P''<sub>m</sub>)<sup>2</sup>, or 0.5625
with a total probability of 1. Similar relationships with diads exist for tetrads.<ref>{{cite journal|title = Configurational Sequence Studies by N.M.R. And the Mechanism of Vinyl Polymerisation|first = F. A.|last = Bovey|authorlink = Frank Alden Bovey|url = http://publications.iupac.org/pac/pdf/1967/pdf/1503x0349.pdf|year = 1967|journal = [[Pure and Applied Chemistry]]|pages = 349–368|volume = 15|issue = 3–4|doi = 10.1351/pac196715030349| s2cid=59059402 }}</ref>{{rp|357}}