300 MHz proton magnetic resonance spectroscopy was applied to the determination of triad structures of three poly(alkyl a-chloroacrylates) of widely varying stereoregularities. Assign­ments and quantitative analyses were made for all of the tetrad peaks in the backbone methylene resonance of poly(methyl a-chloroacrylate), poly(ethyl a-chloroacrylate), and poly(isopropyl a­chloroacrylate). In addition the methyl singlet peaks of poly(methyl a-chloroacrylate), the methyl triplet peaks of poly(ethyl a-chloroacrylate) which had not been amenable previously to resolution at 220 MHz, and the methyl doublet peaks of poly(isopropyl a-chloroacrylate) were resolved, and the triad values which were obtained from these pendant ester group resonances compared favorably with triad values calculated from experimental tetrad values. As a demon­stration of the internal agreement of the triad and tetrad peaks assignments, statistical calcula­tions of the stereochemical structures of the atactic and syndiotactic polymers were generally de­scribed well or to a first approximation by random selection statistics (Bernoullian) while the stereochemical statistics of the moderately to highly isotactic polymers were consistent with a nonrandom statistical process (first-order Markovian), as expected.