Optically active (98% ee) (R)-1,1,3,4,4,5,5,5-octadeutero-1-pentene (1) was prepared and used to evaluate the stereoselectivity of Y-H and Y-n-pentyl additions for the optically pure C-2-symmetric (R,S)-(BnBp)Y-R(S,R)-(BnBp)Y-R and racemic (+/-)-(BnBp)Y-R isospecific polypropylene catalysts (BnBp = {(OC10H6C10H6O)Si(C5H2-2-SiMe(3)-4-CMe(3))(2)}). Deuteration and deuterodimerization of 1 mediated by (R,S)-, (S,R)-, and (+/-)-(BnBp)Y-D provide alkanes whose H-1 NMR spectra indicate the sense and magnitude of olefin facial selectivity for insertions into metal-hydride and metal-n-pentyl bonds. It is shown that useful information concerning the stereochemistry of olefin insertion can be deduced from the H-2 NMR spectra of 1-pentene deuterodimers without the requirement of a stereochemically labeled pentene or a resolved catalyst.