[MackTuesday]

The web has many online databases of properties of compounds locked behind search interfaces, but I can't find anything you can actually download.

I want a corpus of data that might allow me to, say, sort compounds by enthalpy of formation, or melting point, or other properties you'd encounter in a high school chemistry class. I don't need environmental impact properties, or toxicology data, or even molecular structure, and I don't need to know about exotic stuff hardly anyone's ever heard of. Just the basic simple things you would expect to be easily available like just about everything else on the web.

There are handbooks of general properties of compounds. Collections like these are perfect. Surely someone has put information that exists in a book into digital format.

I don't mind paying for it. But I can't even find it.

[Enthalpy]

Hi MackTuesday,

I don't know of any comprehensive database available legally on the Internet. For the most common compounds, try the NIST's one, whose data is more credible than others. There
http://webbook.nist.gov/cgi/formula/C8H16
you access a list of compounds through their formula, C₈H₁₆ in this case. But they are not ordered by properties, and most compounds are paywalled.

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As you don't mind paying, a good option would be the
CRC Handbook of Chemistry and Physics
whose latest edition on paper is a bit expensive, but used or older ones are affordable
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=CRC+Handbook+of+Chemistry+and+Physics
I got a but-latest edition, new, for <50€ on eBay.
The paper edition has lists of compounds ordered by melting point and by boiling point.
That's my recommendation for being more complete and convenient. It contains much more data, often useful.

The same CRC Hdbk is accessible online behind a paywall, I didn't try:
http://www.crchandbook.com/

Excerpts of the CRC Hdbk exist on the Internet as Pdf, especially the table for heat of formation, probably scanned and probably infringing copyrights. Though, I feel it morally acceptable to use these files if you already own a paper version.

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Chemister looks very interesting and is an online database:
http://chemister.ru/Database/search-en.php
Rather than the built-in search, I prefer to use Google:
compoundname site:chemister.ru
Free, organized by compound but not ordered by property, one mistake from time to time, very complete set of properties.

Egloff is a good book. Less complete than the CRC Hdbk, but credible.

FIZ is a good online database. I don't find the details right now.

Just Wiki is rather good. Organized by compound, but it also contains some lists of compounds and properties, for instance for branched alkanes.

Very few compounds for free at www.ddbst.de

Beilstein is a classical reference, too expensive for me, and seems difficult to use.
Comcast would be a spreadsheet, hence searchable, free to download, but inaccurate. For instance, the heat of formation refers inconsistently to the gas, liquid or solid, without telling.
Don't waste a cent on Yaws: it's a complete big book made by software estimation of properties, hence wrong.

You mentioned melting points: expect to be disappointed. Very few have been measured. The rest is estimated hence very wrong. Other properties too are often estimated on the Web, but boiling points for instance are less wrong. Check each and every time if the data is experimental; it's good practice to ask for isomers and observe if their data differs.

[MackTuesday]

Thanks. I'll see what I can do with your suggestions.