Tacticity

Generally, tacticity applies to addition polymers with one non-hydrogen substitute attached to the carbon chain for each monomer unit:

    H   H 
    |   |      
-(- C - C -)-
    |   |
    H   R

Tacticity has to do with which side of the chain the R group is placed (this contrasts with head-tail placement which has to with which carbon the R group is placed on.) Fischer projections can be used to show the three different types of tacticity:

Isotactic

Notice that all of the R groups line up on the same side.

Syndiotactic

Notice that the R groups alternate from side to side.

Atactic

Notice that the side to side positioning is random.

You will notice that in all the illustrations below, as you go along the carbon chain, one carbon has an R, the next carbon doesn't, the next carbon has an R, the next carbon doesn't. This has nothing to do with tacticity, but rather, concerns head/tail placement.

Last Update- March 14, 1995- wld