I'm looking for a comprehensive reference of experimental specific rotation or optical rotation data. It can be a published literature review, a free web database with API access or one that permits scraping, or even a table on a web page with references.
ChemSpider pages link to outside sources (I think only chemical suppliers) for optical rotation, but this is problematic:
- it's unclear what molecules contain this information (not all stereoisomers do),
- not all the product specification pages on the suppliers' websites actually contain the data,
- the values aren't available through the ChemSpider API, and
- it's forbidden to screen scrape ChemSpider pages.
The story seems to be similar for PubChem, though they allow scraping within reason.
For example, here is a review collecting experimental electron affinities for a large number of small molecules and elemental clusters. It's fine that this isn't web-based, because all the values are together and in bulk; writing a PDF scraper is worthwhile because there are so many entries.
Also acceptable would be a book, such as the comprehensive reference from Huber and Herzberg that contains rotational constants, bond lengths, and other constants for diatomic molecules.