There is a very good article on the Royal Society of Chemistry [RSC] website on the chemistry of "whisky" and the theory behind adding a "bit" of water to "open up" our favorite beverage.
It can be viewed HERE.
OK, its geared towards Scotch whisky, but it explains why bourbon can have that hint of sweet vanilla. The article also has a "flavor" wheel, which lists what organic compound families can contribute to the nose and flavor profiles of whiskey.
As a new member, I tried to search and see if this link had been previously posted. If I missed it and it has, I apologize.