Green notes come in all shapes and sizes, and selecting the best combination for any given flavor profile is one of the most interesting challenges that flavorists routinely face. Green notes are usually, but not always, secondary to the key character recognition aspects of a flavor s profile, so they should provide an impression of, say, freshness, rather than imposing too much of their own character. trans-2,cis-6-Nonadienal (FEMA# 3377, CAS# 557-48-2) is a very powerful green note that is highly characteristic of fresh cucumbers. It is clearly an essential component of cucumber flavors and can also find a number of uses where a more subtle cucumber note is desirable, or at least acceptable. Outside this narrow field the use of this chemical is rather limited by its highly specific profile.
The most obvious alternative with a similar profile is trans-2,cis-6-nonadienol (FEMA# 2780, CAS# 28069-72-9). This chemical has, in my opinion, a vastly more attractive, soft and natural cucumber character and wider range of uses than the aldehyde. Nevertheless, it is still somewhat limited by its instantly recognizable affiliation to cucumbers.