Are there compounds that have the same SMILES code but are not stereoisomers? I am trying to find inconsistencies with SMILES code and currently I have that many compounds have multiples options for SMILES code but I want to find if there is a SMILES code that can represent multiple compounds.
Many SMILES for single structures
There are many, many valid SMILES for most organic structures. For example,
C(O)C are all valid SMILES for ethanol.
Many structures for single SMILES?
There are probably cases where the same SMILES can represent multiple compounds, but most of these probably involve transition metal complexes, which SMILES is (I think) widely regarded as not handling very well, or else cases where what is meant by "compound" is also ambiguous. E.g. are "ethenol" and acetaldehyde are arguably both represented by
C=CO, but in order to see that you need to know about keto-enol tautomerism.
The SMILES corresponds to the underlying molecular graph (with bonds being edges and atoms vertices). This means the question you are asking is "are there any molecules that are different, not stereoisomers, and have the same underlying molecular graph".
The answer to this is yes. One typical example is atropoisomers (due to conformational barriers), though this can also be considered stereoisomery depending on how strict you are. This is actually relevant, for example in the kinase field some biaryls will show atropoisomerism. Another example is topological isomery. Imagine a trefoil knot C100 cycloalkane vs the ordinary C100 cycloalkane. Same graph, so same SMILES. However, in most typical uses of SMILES, these type of issues can be considered purely curiosities.