lass="o">.</span><span class="n">get_special_carbon</span><span class="p">(</span><span class="n">elements</span><span class="o">=</span><span class="n">elements</span><span class="p">)</span>
        <span class="n">groups</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">link_marked_atoms</span><span class="p">(</span><span class="n">heteroatoms</span><span class="o">.</span><span class="n">union</span><span class="p">(</span><span class="n">special_cs</sp