\newbox\monomera\setbox\monomera=% \structure{\nopositioncheck\esingle\atom{C} \side{\nsingle\atom{C}\epin{H$_3$}} \atom{H}\esingle\atom{CH$_2$}}% \newbox\monomerb\setbox\monomerb=% \structure{\nopositioncheck\esingle\atom{C} \side{\ssingle\atom{C}\epin{H$_3$}} \atom{H}\esingle\atom{CH$_2$}}% \newbox\monomere\setbox\monomere=% \structure{\nopositioncheck\esingle\atom{C} \side{\nsingle\atom{C}\epin{H$_3$}} \atom{H}\esingle\atom{CH$_2$}\esingle\phantatom{}}% \vbox{ \centerline{\copy\monomera\copy\monomera\copy\monomera% \copy\monomera\copy\monomera\copy\monomere} \medskip \centerline{\copy\monomerb\copy\monomera\copy\monomerb% \box\monomera\box\monomerb\box\monomere} \medskip \centerline{\bf Figure~11. \rm Isotactic and syndiotactic polypropylene.} }