Is there an intramolecular hydrogen bond in guaiacol?

Is there a hydrogen bond between the $\ce{H}$ atom of $\ce{-OH}$ group and the $\ce{O}$ atom of the $\ce{-OCH3}$ group in ortho-methoxyphenol? I was told no. But I want to know why.




According to a quick calculation on the DF-BP86/def2-SVP level of theory, there is an intramolecular hydrogen bond with a strength of about $\ce{-26.6 kJ/mol}$ according to a quantum theory of atoms in molecule (QTAIM) analysis.


[![laplacian plot](https://i.stack.imgur.com/Sl2bd.png)](https://i.stack.imgur.com/Sl2bd.png)


For an explanation of the evaluation of the bond strength see: E. Espinosa, E. Molins, C. Lecomte. *Chem. Phys. Lett.* **1998,** *285*, 170-173.  

Analysis done with [MultiWFN 3.3.8](http://sobereva.com/multiwfn/). Calculations with Gaussian 09 D.01.


 4

Ortho-methoxyphenol actually can form an intramolecular hydrogen bond, but this can be altered by protic hydrogen acceptor solvents such as DMSO. See <https://www.ncbi.nlm.nih.gov/pubmed/19473035> (abstract available in front of the paywall).


 3

I recommend looking up the relevant bond lengths and seeing if the H and the O "match up" at the right distance to form a hydrogen bond, as dictated by the geometry of the molecule. H-bonds tend between 1.6 and 2 angstroms. 


Also note that the most effective hydrogen bonds have all three atoms co-linear (X-H~X); the hydrogen bond becomes weaker as the angle deviates from 180°. You could find the theoretical angle your three H-bonding atoms will share (assuming the distance is reasonable for an H-bond to occur in the first place), and consider how much this angle deviates from 180°. 


This [brief article](http://w3.iams.sinica.edu.tw/lab/jlli/thesis_andy/node5.html) mentions models that include the H-bond energy's dependence on the H-bond angle, where the H-bond energy is proportional to some power of the cosine of the angle:


$$U \propto \cos^n(\theta)$$


By this model, when the angle becomes a right angle (a "side-on" H-bond), the potential energy rises to zero. An H-bond in this perpendicular orientation is no longer a stabilizing interaction. So you will want your angle to be between 180° ($\pi$) and 135° ($3\pi/4$) or so to have an interaction worth calling a hydrogen bond.


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