These are the meta atoms that are needed to define groups in the Benson rule definitions
cR2//o BensonAldehydeKetone co BensonAtom
oR2 BensonSP3Oxygen o BensonAtom
cR2//R BensonDoubleBondCarbon c/d BensonAtom
cR///R BensonTripleBondedCarbon c/t BensonAtom
nR3 BensonSingleBondedNitrogen n BensonAtom
cR4 BensonCarbonAtom c BensonAtom
nR3 BensonSingleBondNitrogen n BensonAtom
n(//nR)R BensonAzoNitrogen n/a BensonAtom
n(//R)R BensonIminoNitrogen n/i BensonAtom
n(//o)oR BensonNO2 no2 BensonAtom
n(//o)R BensonNO no BensonAtom
c(///N)R BensonCN cn BensonAtom
s(//o)2(/oR)2 BensonSO4 so4 BensonAtom
s(//o)2R2 BensonSO2 so2 BensonAtom
s(//o)2(oR)R BensonSO3 so3 BensonAtom
s(//o)2(oh)R BensonSO3H so3h BensonAtom
s(//o)R2 BensonCO so BensonAtom
sR2 BensonSP3S s BensonAtom
R/o/o/R BensonPeroxyGroup oo BensonAtom