an> <span class="k">for</span> <span class="n">n</span> <span class="ow">in</span> <span class="n">neighbors</span> <span class="k">if</span> <span class="n">n</span><span class="p">[</span><span class="s2">&quot;site_index&quot;</span><span class="p">]</span> <span class="ow">in</span> <span class="n">hydrogens</span><span class="p">}</span>
                <span class="c1"># Methyl group is CH3, but this will also catch methane</span>
                <span class="k">if</span> <span class="nb">len</span><s