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Flavour and Fragrance Models: Leffingwell Odour Threshold

Apr 26, 2018

Flavour and Fragrance Models: Leffingwell Odour Threshold

Apr 26, 2018

To be smelt a compound has to have a low enough vapour pressure to be in the gaseous state and have sufficient affinity/efficacy at olfactory receptors. A related measure of volatility is odour threshold.


A data set was collected from the web pages (accessed Jan2018) created by Dr John C. Leffingwell. It details the odour thresholds of various chemical classes where chirality modifies the odour descriptions of the enantiomeric pairs.

The full data set contains over 700 enantiomeric pairs, however, only 422 compounds had suitable data for modelling the odour threshold quantified in ppb. The data range for this set was extremely large, covering more than 10 orders of magnitude and so the log of the ppb data was modelled. Where compounds were listed as “odourless” a value of 7 was used as a default; ppb values of ‘-3’ and ‘1’ were used to classify the set. As the StarDrop descriptors are unaware of chirality the category boundaries were chosen to cope with the changes in threshold which were solely due to changes at the chiral centre(s).


The best model produced was a Random Forest model.

Using the Leffingwell Odour Threshold Model

The model can be downloaded for use within StarDrop from the following link:


To use this model within StarDrop, download and save the fil in a convenient place. Load it into StarDrop using the  button on the Models tab. Alternatively, the directory in which the model file has been saved can be added to the paths from which models are automatically loaded when StarDrop starts by selecting the File->Preference menu option and adding the directory under Models in the File Locations tab.