Identify functional groups that cannot be identified by the Ertl method
        of get_special_carbon and get_heteroatoms, such as benzene rings, methyl
        groups, and ethyl groups.

        TODO: Think of other functional groups that are important enough to be
        added (ex: do we need ethyl, butyl, propyl?)

        :param func_groups: List of strs representing the functional groups of
            interest. Default to None, meaning that all of the functional groups
            defined in this function will be sought.
        :return: list of sets of ints, representing groups of connected atoms

def get_basic_functional_groups(self, func_groups=None):
        """
        Identify functional groups that cannot be identified by the Ertl method
        of get_special_carbon and get_heteroatoms, such as benzene rings, methyl
        groups, and ethyl groups.

        TODO: Think of other functional groups that are important enough to be
        added (ex: do we need ethyl, butyl, propyl?)

        :param func_groups: List of strs representing the functional groups of
            interest. Default to None, meaning that all of the functional groups
            defined in this function will be sought.
        :return: list of sets of ints, representing groups of connected atoms
        """

        strat = OpenBabelNN()

        hydrogens = {n for n in self.molgraph.graph.nodes if
                     str(self.species[n]) == "H"}

        carbons = [n for n in self.molgraph.graph.nodes if
                   str(self.species[n]) == "C"]

        if func_groups is None:
            func_groups = ["methyl", "phenyl"]

        results = []

        if "methyl" in func_groups:
            for node in carbons:
                neighbors = strat.get_nn_info(self.molecule, node)
                hs = {n["site_index"] for n in neighbors if n["site_index"] in hydrogens}
                # Methyl group is CH3, but this will also catch methane
                if len(hs) >= 3:
                    hs.add(node)
                    results.append(hs)

        if "phenyl" in func_groups:
            rings_indices = [set(sum(ring, ())) for ring in
                             self.molgraph.find_rings()]

            possible_phenyl = [r for r in rings_indices if len(r) == 6]

            for ring in possible_phenyl:
                # Phenyl group should have only one (0 for benzene) member whose
                # neighbors are not two carbons and one hydrogen
                num_deviants = 0
                for node in ring:
                    neighbors = strat.get_nn_info(self.molecule, node)
                    neighbor_spec = sorted([str(self.species[n["site_index"]])
                                            for n in neighbors])
                    if neighbor_spec != ["C", "C", "H"]:
                        num_deviants += 1

                if num_deviants <= 1:
                    for node in ring:
                        ring_group = copy.deepcopy(ring)
                        neighbors = self.molgraph.graph[node]

                        # Add hydrogens to the functional group
                        for neighbor in neighbors.keys():
                            if neighbor in hydrogens:
                                ring_group.add(neighbor)

                    results.append(ring_group)

        return results