I'm not looking for answers that are based on 2013 IUPAC recomendation based rules. But rather the old 1993 rules of IUPAC.

The two names are : 1.) Penta-1,2-dien-5-ol 2.) Penta-3,4-dien-1-ol

would we start numbering from the carbon attached to the main functional group [i.e.,secondary suffix] which would give us locants at 1,3 and 4 or just simply follow the lowest locant rule giving us locants 1,2 and 5 ?

Again, I'm specifically looking for name that be accurate on basis of 1993 IUPAC rules and not the PIN.

What rules to keep in mind while naming this ?


1 Answer 1


Concerning numbering of locants according to the recommendations of 1979, 1993, as well as 2013, the lowest locant is given first to the principal group that is named as suffix (here: -ol) and then to unsaturation (ene/yne).

Thus, the correct name according to the 1993 and 2013 recommendations is penta-3,4-dien-1-ol. (The 1979 recommendations had a different placement of locants in the name.)

See also this example given in the 1993 recommendations: pent-4-en-2-ol


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