Hi Ultima, may i ask you,
I know the priority of the functional groups for aliphatic
molecules as shown here :
https://www.dropbox.com/s/25ncr8p5i5y1e9x/20150107_153638-1.jpg?dl=0
However may i ask about the priority of the functional groups
for aromatic molecules?
I was confused about this :
https://en.m.wikipedia.org/wiki/2-Nitrotoluene
Its called 2nitromethylbenzene here, i.e. toluene has higher
priority?
Compared to
https://en.m.wikipedia.org/wiki/Chlorotoluene, 1-chloro-2-methylbenzene ,
i.e. chlorine has higher priority here?
As far as professional chemists are concerned, so-called priorities
of functional groups in naming organic molecules (in contrast,
Cahn–Ingold–Prelog priority rules are clear, logical and must
be consistently followed for uniformity and unambiguity's sake) are
merely IUPAC guidelines (not strict rules), what's far more
important (and critical) is that the species is unambiguously
identified. Which means there are multiple correct or acceptable
names for most organic molecules. For instance, look at the "Other
names" below the "IUPAC name" for 2-Nitrotoluene here : https://en.wikipedia.org/wiki/2-Nitrotoluene.
All these "other names" are also correct, IUPAC is a just a
guideline.
For A level purposes, Cambridge too, allows for flexibility in
naming as long as it is unambiguous. And on a more relevant and
practical note for JC students, is that Cambridge doesn't test
naming much at A levels, the question can give a complex name for
an organic molecule and the student must be able to draw it out,
but not vice-versa.
As a general rule (remember Chemistry, like real-life, must be
intelligent and sensible, not dogmatic and meaningless), instead of
memorizing priorities from your school lecture notes, just ask
yourself, which functional group is more chemically reactive (ie.
the most nucleophilic, electrophilic, lower Ea, etc), then such a
functional group should be highlighted first in the name (because
the most reactive functional group defines the molecule's most
important properties), and hence give it priority. Do this because
it makes intelligent sense to do so, not because your school
lecture notes dogmatically say so.
PS. Just like how you (ie. everyone reading this) are advised to
always be an intelligent, free-thinking
individual who is self-responsible for what you choose to believe,
be the captain of your own soul, instead of blindly following
religious dogma of any religion.
