1
is given priority over 
Is corrosion an electrochemical phenomena ??/
The IUPAC name of the compound with the structural formula CH3 - CH = CH - C CH is
(A)pent-2-ene-4-yne
(B)pent-1-yne-3-ene
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15 Answers
4@Manmay : Wahi tho doubt hai mera !! :(
Y is it electrochemical ???
@Ray : I know that is the priority order But c 2009 JEE nomenclature qs it says locant rule given more priority that priority order
11I feel the answer is b
because double bond given preference over triple bond only when they are at identical positions....
?????
4ya Sandipan even mine was the same doubt
Anyone having a confident ans plzz explain ??
1Hmmm...
Sandipan bhai, correct.
The answer shud be (B) coz it follows the lowest sum rule. Only wen both bonds occupy identical positions, priority rule is followed.
Such compounds are termed as alkenyne(not alkynene)
[IUPAC- 1993]
11http://www.cem.msu.edu/~reusch/VirtualText/nomexmp1.htm#exp6
see example 9,10,11
1For the first one,
Rusting is an electrochemical phenomenon coz just like in any electrochemical cell, here too oxidation and reduction takes place. Iron is oxidised (as in anode) and O2 is reduced (as in cathode), simultaneously. All this occur in presence of moisture.
11http://electrochem.cwru.edu/encycl/art-c02-corrosion.htm
for that corrosion one....
39That priority waala problem is well known...IUPAC has weird rules. You have to rattofy whatever answer there is.
1yes agree with ray on #10.
add to it that CO2 is needed as well to provide acid in water which gives H+ ions.
4Thanks everyone for 1st one
and second is still a MISTERY of CHE" MISTRY "
13Nah....there is a particular order fr NomenClature, i wrote it smwhere, will try n find out.
13Finally, there....
Mark my words, follow the steps below n u'll hardly ever find urself stuck in probs such as these... the sequence is 100% trustworthy. [1]
I- The Chain
Nomenclature mein the first step is finding the longest C-chain (or the one containing max. = n triple bonds)
II- Identifying nearest locants
The second step is finding the nearest locant position (regardless of its type)...(=/triple bonds r also considered as locants)
III- Proper Numbering
Agar chain ke dono end se nearest locant par diff. group hain THEN ONLY u will start assigning the Priority..... or agar same hi groups hain THEN u will go for the Lowest sum rule...
[NOTE: Lowest sum is not to be accounted for when there are different priority groups as nearest locants, then we got to go by priority ONLY.]
The most Imp Rule :: Without doing one step; u can't jump 2 the next..
Thts it! Though its not completely enuf, but fr now... :P
So, in the compound....main chain is the st. one with 5-C(s)...... then v have nearest locant @ C-1 frm right as compared to @C-2 frm left.
(Priority comparison ka sawaal hi nahi...!!)
Start numbering frm the RIGHT.
Finally name ----- Pent-3-en-1-yne