Hydrogens in Reactions:

• Hydrogens normally may be omitted from SMILES. Only for certain "special" cases must hydrogens be shown. These cases include:

• Charged hydrogens ([H+]),

• hydrogens connected to other hydrogens, ([H][H]),

• hydrogens connected to more than one atom,

• isotopic hydrogens ([2H]).

For reactions, if a hydrogen is mapped, it is also "special" and must be shown.

[CH2:1]=[CH:2][CH:3]=[CH:4][CH2:5][H:6]>> [H:6][CH2:1][CH:2]=[CH:3][CH:4]=[CH2:5]