The ASTM software Chemical Thermodynamic and Energy Release version 9.0, CHETAH 9.0, has many useful features for calculating thermodynamic values of substances.  My interest is in the (gas phase) calculation of ΔHf, limiting oxygen concentration, lower flammability level, Cp, entropy, ΔG, maximum heat of decomposition, net plosive density, ΔHc, and minimum ignition energy. The package claims to have the largest known database of Bensen group values at 965 entries.

I would have supplied links but the WordPress Editor is on the fritz. One more bloody software “issue”. – ‘th Gaussling

I recently upgraded from CHETAH 8.0 to 9.0 because 8.0 is incompatible with Windows 7.  These upgrades are a kilobuck a pop so they can be a budgetary surprise. After I upgraded I noted that 9.0 is not compatible with Windows 7 either!! Luckily I have a couple of lab computers that are still XP systems and therefore compatible with 9.0.  The folks at the University of South Alabama write and support CHETAH.

I understand from private communication that CHETAH 10.0 is in the works in anticipation of the release of Windows 8. Oh joy. I hope that some effort will be put into the user interface and general robustness. My question is this- what about those of us who will be using Windows 7 for the next few years? Will rev 10.0 be compatible? Will it have click and drag features or more of a DOS accent like the current rev?

One of the features that is nice about CHETAH is that it accepts SMILES strings as data input.  It parses the string into known Benson groups and flags unknown groups.  Previously I had been entering smiles strings from ChemDraw 7.0, an ancient but still useful version. Lately I have been evaluating ChemSketch freeware.  And lucky for me, I found another hole to stumble into.

SMILES is not inflexible in its syntax, apparently.  ChemDraw will convert a structure to a SMILES string that is different in its sequence from the identical structure drawn by ChemSketch.  I have found that CHETAH 9.0 will consistently accept SMILEs string entries from ChemDraw, but with only some ChemSketch SMILES strings.

Consider the following SMILES strings of the same structure-  5-Bromo-7-tert-butoxy-3-methyl-3H-isobenzofuran-1-one. The nomenclature is from Chemdraw. I do not use this compound- I dreamed it up as an example.

ChemDraw 7.0–  O=C2OC(C)C1=CC(Br)=CC(OC(C)(C)C)=C12

ChemSketch 12–  CC(C)(C)Oc1cc(Br)cc2c1C(=O)OC2C

The ChemDraw SMILES string is accepted by CHETAH 9.0 and parsed into Benson groups, but when you attempt to process the data it gives a “Run-time error 9” warning and then closes the program. From what I can tell, CHETAH 9.0 will only accept 9 Benson groups because when you clip off functional groups, it will accept the string for the next step. However, it still shuts down and indicates another error saying “subscript out of range”. I don’t know why this happens and the handbook does bnot seem to list errors. The programmer put the error routines in the program, but I guess was too busy to tell anyone what they mean.

The ChemSketch SMILES string above is not accepted at all.

I cannot justify switching to ChemSketch for several reasons and this is one of them.  The ChemSketch editor is generally balky compared to the smooth operation of ChemDraw. However, I must say that ChemSketch is very feature rich and has gotten much better. If I wasn’t already committed to ChemDraw (and Chem3D) I’d strongly consider it.

CHETAH seems to have limitations on the number of Benson groups it will accept for a molecule. It seems to require a particular edition of SMILES syntax. And, the user interface is is balky and antiquated.  I’ll try to uninstall CHETAH and reinstall it. That said, it still seems … brittle.

From what I can piece together by googling SMILES, the system has been evolving. Apparently, chemical graphics software out there has captured particular editions of SMILES at the time when their revision is released.  It would be nice if some international standard were in place to devise an enduring syntactical structure. Seems like something CAS could help with.