The chemicals that are reaching your nose are a complex mixture, the culmination of distillation and years maturation. But they are not a fixed set, you can still alter and change the bouquet that greets your nose and so the flavour of the whisky simply by adding water. Adding water to whisky changes the concentration of alcohol and so increases the volatility of alcohol-soluble hydrophobic or long-chain compounds such as the fruity esters, increasing the fruity aspects of the whisky's flavour.
In contrast, smoky phenolics and roasted nut and cereal-flavoured nitrogen-containing compounds are water-soluble, and the volatility of these is reduced with water addition and so the smoky aspect of the whisky's flavour is reduced. However, the addition of ice reduces the temperature of the whisky and hence reduces the volatility of all the compounds, leading to a reduced aroma and a diminished taste.
Which is why you should never, never add ice to your single malt.
I've just bought an eye-watering Bruichladdich single cask whisky. Single cask means the whisky has come straight from the cask it's matured in, and not mixed with anything. This whisky is undiluted, so it's a whacking 66% alcohol. The whisky you buy in the shops or most bars is always watered down to make it more palatable to the average imbiber. It's ready-diluted, at around 40%. The beauty of my whisky (from the Scotch Malt Whisky Society) is that I can water down the neat spirit to suit my tastes, releasing those delicious flavour molecules as I wish. Or not, if I'm feeling particularly masochistic.