\centerline{
\structure{\nopositioncheck\atom{C}\esingle\atom{C}\nnwsingle
\atom{C}\sswsingle\atom{C}}
\hskip 1truecm
\structure{\nopositioncheck\atom{C}\nsingle\atom{C}\sesingle
\atom{C}\swsingle\atom{C}}
\hskip 1truecm
\structure{\nopositioncheck\atom{C}\nsingle\atom{C}\esingle
\atom{C}\ssingle\atom{C}\wsingle\atom{C}}
\hskip 1truecm
\structure{\atom{C}\nwsingle\atom{C}\nesingle\atom{C}\sesingle
\atom{C}\swsingle\atom{C}}
\hskip 1truecm
\structure{\atom{C}\nnwsingle\atom{C}\nesingle\atom{C}\sesingle
\atom{C}\sswsingle\atom{C}\wsingle\atom{C}}
}
\medskip
\centerline{
\structure{\atom{C}\nwsingle\atom{C}\nsingle\atom{C}\nesingle
\atom{C}\sesingle\atom{C}\ssingle\atom{C}\swsingle\atom{C}}
\hskip 1truecm
\structure{\atom{C}\nnwsingle\atom{C}\nnesingle\atom{C}\esingle
\atom{C}\ssesingle\atom{C}\sswsingle\atom{C}\wsingle\atom{C}}
\hskip 1truecm
\structure{\atom{C}\nnwsingle\atom{C}\nnesingle\atom{C}\esingle
\atom{C}\sesingle\atom{C}\ssingle\atom{C}\swsingle\atom{C}
\wsingle\atom{C}}
\hskip 1truecm
\structure{\atom{C}\nwsingle\atom{C}\nnwsingle\atom{C}\nesingle
\atom{C}\esingle\atom{C}\sesingle\atom{C}\sswsingle\atom{C}
\swsingle\atom{C}}
}
\medskip
\centerline{
\structure{\atom{C}\nwsingle\atom{C}\nsingle\atom{C}\nesingle
\atom{C}\esingle\atom{C}\sesingle\atom{C}\ssingle\atom{C}
\swsingle\atom{C}\wsingle\atom{C}}
\hskip 1truecm
\structure{\atom{C}\nwsingle\atom{C}\nnwsingle\atom{C}\nsingle
\atom{C}\nesingle\atom{C}\esingle\atom{C}\sesingle\atom{C}
\ssingle\atom{C}\sswsingle\atom{C}\swsingle\atom{C}}
\hskip 1truecm
\structure{\atom{C}\nwsingle\atom{C}\nnwsingle\atom{C}\nnesingle
\atom{C}\nesingle\atom{C}\esingle\atom{C}\sesingle\atom{C}
\ssesingle\atom{C}\sswsingle\atom{C}\swsingle\atom{C}\wsingle
\atom{C}}
}
\medskip\centerline{\bf Figure~2. \rm 
Three- to ten-membered carbon rings.}