For the systems involving SAMPL7 molecules SM30, SM33, SM34, SM36, SM37, and SM39, additional 100 ns NPT simulations were performed to generated sufficient statistics for structural analysis to better understand the effect of inclusion of water in the octanol-rich phase; we only considered TIP4P water which was used in our SAMPL7 entries. Here we focus on SM33, SM36 and SM39 to highlight the role of water. Structurally, the three molecules differ only in the sulfur group in the four membered ring. For SM33, SM36, and SM39 we have a sulfide, sulfoxide, and sulfone group, respectively. (See figure ). The difference between log 10 P o * /w 1 and log 10 P o/w 1 is -0.87, 2.05, and 0.61, for SM33, SM36, and SM39, respectively. For the case of SM36 this is the largest increase of all of the SAMPL7 molecules, and for SM33 this is the largest decrease of all of the SAMPL7 molecules. And interestingly SM39 falls in between close to the observed average change for the SAMPL7 set. The structural analyses were all performed using TRAVIS .