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Ask iit jee aieee pet cbse icse state board community Community Discussion Question: Nomenclature-simple but doubful
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varshavallig (798)

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in the nomenclature of haloalkanes,which one shud b given more preference:Cl or Br.how do v know it?
i got this Question in my exam:
Cl-CH2-CH2-CH2-Br.
 
i wrote it as 1-bromo,4-chloro propane.
is it rite???????
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Varsha
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Greatdreams (3155)

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I think you are correct .Among the different halogens

preference is given alphabetically that is Br is preferred

over Chlorine which is preferred over Fluorine which is

further preferred over Iodine.


So the name of the compound is 1-bromo,3chloro propane


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Ashish (95)

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Hiiiiii

You are right. In case of two substituent groups that with equal preference and equal locants in the various options that are possible, the one higher up the alphabetical order is supposed to be listed first and given the lower locant.

Hope it helped!

'Your eyes show the strength of your soul.'
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varshavallig (798)

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thanx a lot!!!
but i read in a book that preference should be given to the heavier one.is it correct?
!!!!!!!!

Varsha
be cool,
tomorrow is what we make it today,
so if u can dream it , u can make it .
life is an ice cream ,eat it before it melts away!!!!!!!!!
varsha

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Ashish (95)

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I think not. Preference is given to the one higher up the alphabetical order only.

'Your eyes show the strength of your soul.'
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crack (380)

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hello........there is only 3 carbon atoms
how can it be 1 -bromo,4chloro propane...
shouldn't it be 1-bromo,3-chloro propane

<TABLE CELLSPACING="1" CELLPADDING="1" BORDER="0">
<TR><TD>


<DIV ALIGN="right">Glitter Graphics</DIV></TD></TR></TABLE>
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bhartibhanushali (249)

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there r 3C hence propane
it does not matter whether we write Bromo first or vice versa
but for sake of convenience we just take it in alphabetical order
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crack (380)

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sorry bharathi....
i am afraid you are wrong......
according to iupac the substituents should always be arranged in
alpabetical order......
there is a system that is given by an authority...... and we are suppose to follow it......

<TABLE CELLSPACING="1" CELLPADDING="1" BORDER="0">
<TR><TD>


<DIV ALIGN="right">Glitter Graphics</DIV></TD></TR></TABLE>
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faizameer (25)

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I agree with crack....
We should follow alphabetical order.It is there latest IUPAC naming system
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sweet_gal (0)

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the answer is 1-bromo 3-chloro propane.......
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saurabhpanda (36)

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crack is right but
what if an nitro grp is present which one will be prefered
no2 because of alphabet or because of  heaviness
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learner (325)

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There is a list of priority for functional groups...btw nitro and halo you'll have to check that and name accordingly..
The alphabetical order for functional groups comes into play only when you have different atoms of the same group...eg in halo, chloro,bromo have same priority,so here we see alphabetical order
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