\starttext

    % pyrimidines

    \startchemical
        \chemical [SIX,SB123456,SR156,DR3,Z13456,CRZ35] [C,C,N,C,C,O,H]
        \chemical [Z2,RZ1,CRZ6] [\SL{N|NH},\SL{NH_2|O},H|CH_3] % C&T
    \stopchemical

    \startchemical
        \chemical [SIX,SB123456,SR156,DR3,Z13456,CRZ35] [C,C,N,C,C,O,H]
        \chemical [Z2,RZ1,CRZ6] [\SL{N|NH},NH_2|O,H|CH_3] % C&T
    \stopchemical

\stoptext
