Peter…you comment

“PMR: This is a scientific experiement to see if Quantum mechanical methods can predict NMR shifts. The emphasis is on Quantum Mechanics. Does Quantum Mechanics agree with experimental data?”

That’s known I thought. There are tens of papers out there already where this has been shown. You’ve commented on this re. Hexacylinol yourself, a famous example of GIAO application. So, it’s at best a repeat experiment, one conducted many times.

The inclusion of spin-orbit coupling into GIAO NMR predictions has been discussed previously a decade ago:

http://www3.interscience.wiley.com/cgi-bin/abstract/5008678/ABSTRACT?CRETRY=1&SRETRY=0

Note the abstract re. normal halogen dependence

“Spin-orbit coupling is responsible for many heavy-atom effects on NMR chemical shifts, for example, normal halogen dependence. A simple but general model for spin-orbit-induced substituent effects has now been developed by analogy to the Fermi contact spin-spin coupling mechanism (see below). DFT calculations on some simple iodo compounds illustrate the scope and validity of the model.”

The upfield shifts you talked about here http://wwmm.ch.cam.ac.uk/blogs/murrayrust/?p=732 regarding the halogens are well-known effects. You commented “the effects can be calculated, and are somewhat basis set dependent. For our basis, Br should be corrected by -12 ppm (and approx -24 for two) and Cl by -3 ppm. S is probably -2ppm, and Iodine -28 ppm. That should probably suffice for the halogens.”

I’ve done a lot of heavy metal NMR over the years. One Chapter of my PhD focused on pressure and temperature dependent shifts of Co-59 (http://www3.interscience.wiley.com/cgi-bin/abstract/88511686/ABSTRACT). During that work I read a lot about the theory of chemical shifts and specifically the work of Cynthia Jameson. At the same time I was examining the temperature dependence of C-13 shifts in octyl halides …the temperature-based shift dependence of the Carbon alpha to the halogen was significant for all halogens increasing from F through to I. I recalled reading about the normal halogen dependence and it’s connection to spin-orbit coupling at that time.

A quick search on google on “spin orbit normal halogen dependence” gives as a top hit:

http://pubs.acs.org/hotartcl/cenear/980928/nmr.html

This contains the following nugget:

“…carbon-13 in iodomethanes, were shifted far upfield, way out of character for what was expected. This is called the normal halogen dependence.

Eventually, in 1969, Japanese theorists determined the effect was due to spin-orbit coupling… ”

Looks like the effect you’ve noticed was first explained about 40 years ago.

Ain’t the web great?

In regards to GIAO vs HOSE, Neural Net and Increment based methods we were hoping to get a good data set for comparison out of your work. What we’ve done in the meantime until the entire dataset is online for us to compare is to look in the literature for GIAO NMR calculations. We’ve got over 30 publications out of the literature to data and have done the comparable predictions. I’ll blog about it soon…it’s consistent with expectations.

A new article is now available on JCIM ASAP entitled, Toward More Reliable 13C and 1H Chemical Shift Prediction: A Systematic Comparison of Neural-Network and Least-Squares Regression Based Approaches 10.1021/ci700256n A very interesting read for those…