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The SMARTS format is a language for matching substructures of chemical files and was created by Daylight Chemical Information Systems, Inc. alongside the SMILES format.

Specification URL

Limitations of the Open Babel SMARTS Implementation

The Open Babel implementation of SMARTS is not bug-free, nor does it support everything in the Daylight Toolkit. In particular, it is known to not currently support:

  • Cis/trans double bond stereochemistry. Feature Request
    • Note: The SMARTS '/' and '\' notation will be accepted, but will not restrict to cis/trans functionality. Instead these bond notations are treated equivalently to a single bond.
  • Tetrahedral stereochemistry involving a lone pair (e.g. at a sulfoxide)
  • Component-level grouping (i.e., "(C).(C)") Feature Request
  • Use of non-tetrahedral chirality Feature Request
  • Unspecified chirality (i.e., "@?") Bug Report

This list may not be complete. Please e-mail the openbabel-discuss mailing list if you have questions about the SMARTS support in Open Babel.

Open Babel Extensions to SMARTS Syntax

In addition to the Daylight Toolkit syntax, Open Babel also offers the following extensions to SMARTS which are not currently supported by Daylight:

  • Atom hybridization matching "^". For example [#6^3] matches a carbon atom (atomic number 6) with sp3 hybridization. Accepted hybridizations include:
    • 1 - sp e.g., [#6^1][#7]
    • 2 - sp2 e.g., [#6^2][#6^2]
    • 3 - sp3 e.g., [#8^3]