### 2.10. How does InChI differ from SMILES? 

Like InChI, the SMILES language allows a canonical serialization of molecular structure. However, SMILES is proprietary and unlike InChI is not an open project. This has led to the use of different generation algorithms, and thus, different SMILES versions of the same compound have been found.

In fact, one may find at least six different unique SMILES for caffeine on Web sites:

1. [c]1([n+]([CH3])[c]([c]2([c]([n+]1[CH3])[n][cH][n+]2[CH3]))[O-])[O-] 

2. CN1C(=O)N(C)C(=O)C(N(C)C=N2)=C12 

3. Cn1cnc2n(C)c(=O)n(C)c(=O)c12 

4. Cn1cnc2c1c(=O)n(C)c(=O)n2C 

5. O=C1C2=C(N=CN2C)N(C(=O)N1C)C 

6. CN1C=NC2=C1C(=O)N(C)C(=O)N2C 

 

![img](../media/02_10-1.png )