SRU.java

    SmilesParser smipar = new SmilesParser(SilentChemObjectBuilder.getInstance());

    String smi = "*CCO*";
    IAtomContainer mol = smipar.parseSmiles(smi);

    Sgroup sgrp = new Sgroup();
    sgrp.addAtom(mol.getAtom(1));
    sgrp.addAtom(mol.getAtom(2));
    sgrp.addAtom(mol.getAtom(3));
    sgrp.addBond(mol.getBond(0)); // bond crossing bracket (xbond)
    sgrp.addBond(mol.getBond(3)); // bond crossing bracket (xbond)
    sgrp.setType(SgroupType.CtabStructureRepeatUnit);
    sgrp.setSubscript("n");
    sgrp.putValue(SgroupKey.CtabConnectivity, "ht");

    mol.setProperty(CDKConstants.CTAB_SGROUPS, Collections.singletonList(sgrp));

    SmilesGenerator smigen = new SmilesGenerator(SmiFlavor.CxSmiles);

    String cxsmi = smigen.create(mol);