C		CH4
[C]                           C atom
[CH0]		C atom
C[2H]		CH3D
C[1H]		CH4 
[C]([H])[H]	CH2  carbene
[C][H]	CH    
[CH]	CH
[CH][2H]  CHD
C[2H]      CH3D
[H][H]	H2
C[O]        methoxy radical CH3O 
[2H][H]		HD
C([2H])[2H]	CH2D2
[CH0]([2H])[2H]	CD2
[S].[O].[Cl].[Cl]       SOCl2
[Na+].[Br-]               NaBr
[Na+].[At-]               NaAt
NC(N)=[NH2+].[Cl-] guanidine hydrochloride CN3H6Cl
ON=O           HNO2 nitrous acid
ON(=O)=O   HNO3 nitric acid
O[N+]([O-])=O HNO3 nitric acid
[N][O]            NO
[N]=O            NO
[N](=O)=O    NO2
[O-][O+]=O O3
C[N+]#[C-]  CH3NC
CC(=O)O          acetic acid
[Na+].CC(=O)[O-]          sodium acetate NaC2H3O2
[K+].N(=O)(=O)[O-] KNO3
C[N+]([O-])=O nitromethane CH3NO2
COOC          dimethyl peroxide C2H6O2
COO            methyl hydroperoxide CH4O2
CO[O]         methly peroxy radical CH3O2
[OH3+].Cl(=O)(=O)(=O)[O-]  hydrated perchloric acid H3ClO5
S		hydrogen sulphide   H2S
CS		methyl mercaptan    CH4S
C=S		thioformaldehyde    H2CS
CSC		dimethyl sulphide   C2H6S
CS(=O)C		dimethyl sulphoxide C2H6SO
CS(=O)(=O)C	dimethyl sulphone   C2H6SO2
O=S=O		sulphur dioxide     SO2
O=S(=O)=O	sulphur trioxide    SO3
OS(=O)(=O)O	sulphuric acid      H2SO4
OS(=O)O		sulphurous acid     H2SO3
O[S](=O)=O	radical bug#1938652 HSO3
OS(=O)=O	H added on S        H2SO3
O[S]=O	 	radical             HSO2
S=O		SO molecule         SO
Using the --append formula option
allows a quick comparison of the expected formula, given above, and the one calculated by OpenBabel.
The formula should be independent of whether the 
-h option "Add hydrogens (make explicit)"  is used or not.  
The following lines test an extension to SMILES.
The -e option "Continue with next option after error, if possible"
 is needed to input these - otherwise these
comments are seen as invalid SMILES and the conversion stops. 
Cc                          ethyl radical  C2H5 
c1ccccc1c               benzyl radical C7H7 
c1c(cccc1)c             benzyl radical C7H7
ccc    allyl radical C3H5
Oo    HO2 radical
o      OH radical
[O]   O atom
n=O               NO
n(=O)(=O)    NO2
cccc     C4H6
Cc(C)cCCc(C)cccc(C)cccc(C)ccccc(C)cccc(C)cccc(C)CCcc(C)C lycopene
Os(=O)=O	radical HSO3