International
Tables for
Crystallography
Volume A
Space-group symmetry
Edited by M. I. Aroyo

International Tables for Crystallography (2016). Vol. A, ch. 3.2, p. 774

Figure 3.2.4.1 

U. Müllerb
[Figure 3.2.4.1]
Figure 3.2.4.1

P-helix of isotactic poly-4-methyl-1-pentene (form I) with a 7/2 helix which corresponds to a [7_4] helix in Hermann–Mauguin notation. Large circles represent isobutyl groups (adapted from Natta & Corradini, 1960[link]).