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How to open .CAC files on Windows

To open .CAC files on Windows, confirm the file is intended as a chemical structure file (CAChe MolStruct) and not something from another unrelated app.

Step-by-step instructions

  1. Confirm the file is intended as a chemical structure file (CAChe MolStruct) and not something from another unrelated app.
  2. Use a chemistry converter that explicitly supports “CAChe MolStruct format (.cac/.cache)” to convert the file to a common format you can view (for example, MOL or SDF).
  3. If you use Open Babel tools, be aware the CAChe MolStruct format is documented as write-only in Open Babel, so conversion may require a different tool if you need to read/import .CAC.

Alternative methods

  • Open .CAC in a browser-based viewer if desktop apps fail.
  • Try opening .CAC on Windows with a secondary app to rule out app-specific issues.
  • Convert .CAC only with trusted tools when direct opening is not possible.

Common issues

No app will open the .CAC file

Many systems do not ship with chemical-structure tooling, and .CAC is not a general-purpose format. Also, some toolchains may recognize the type but not actually support reading it.

  1. Verify it is a CAChe MolStruct file (often associated with chemical/x-cache and sometimes paired with the .cache extension).
  2. Use a converter that explicitly lists “CAChe MolStruct format” support to convert it to a widely supported chemical format.
  3. If you attempted to use Open Babel to read/import it, note that Open Babel documents CAChe MolStruct as write-only and try a different tool for reading.

Open Babel (or an Open Babel-based app) cannot import the file

Open Babel documentation states CAChe MolStruct is write-only, so tools built on Open Babel may not be able to open/read .CAC files.

  1. Check the Open Babel CAChe MolStruct format documentation for the read/write limitation.
  2. Use a different converter or the originating CAChe workflow/application to export to another format, then open the exported file.

File type confusion: .CAC used for something else

The .cac extension can be ambiguous across the broader software world; opening it with the wrong kind of program will fail.

  1. Ask the sender what application produced the file and what it contains (chemical structure vs. unrelated data).
  2. Check whether your environment identifies it as chemical/x-cache; if not, treat it as an unknown binary/data file and obtain the correct originating software.

Conversion produces incorrect or incomplete structures

Chemical structure formats can differ in what metadata or structure features they store; conversions may lose information or map fields differently.

  1. After conversion, validate the resulting structure in your chemistry workflow (atoms, bonds, charges, stereochemistry).
  2. Try converting with a different converter/tool if the results look wrong, and compare outputs.

Security note

.CAC (CAChe MolStruct) files are data files, but they are still parsed by complex chemistry libraries; only open/convert files from trusted sources to reduce the risk of parser vulnerabilities.

Back to .CAC extension page