[orgo814]

Quick question. When you draw the formula for 1,4- dichloropentane, you are supposed to have the Cl branching out from the second carbon. If you look up an image of it, that's what it looks like. My question is why? It specifically says 1,4 so I would expect the Cl to be branching off of the first carbon not the second. It just does not make sense to me.

[Hunter2]

I dont understand what do you mean with second C-atom. 1,4-Dichloro-pentan is


Cl-CH₂-CH₂-CH₂-CHCl-CH₃

[orgo814]

My question is why is it not ClCH2CH2CH2CH2CH2Cl. If it is 1,4 dichloropentane, I do not understand why the Cl atom is not bonded to the first carbon.

[discodermolide]

Quick question. When you draw the formula for 1,4- dichloropentane, you are supposed to have the Cl branching out from the second carbon. If you look up an image of it, that's what it looks like. My question is why? It specifically says 1,4 so I would expect the Cl to be branching off of the first carbon not the second. It just does not make sense to me.

Here is 1,4- dichloropentane.
Look here for the rules; http://www.chem.qmul.ac.uk/iupac/class/

[Fluorine]

I'm not understanding either so let's visualizes this a bit and briefly review the basics. Here's the numbering of pentane. Since it's unsubstituted and has no distinct differentiation at any point you can begin numbering from either end.



However as soon as you add a substituent(s) you need to consider which side is the start and which is the end. Take 1-chloropentane. Since the chlorine as been added to first carbon, the opposite end can no longer be 1 and must be position 5.

Cl-CH₂-CH₂-CH₂-CH₂-CH₃ = 1-chloropropane


If you want to add a second substituent to 1-dichloropropane and make it, for example, 1,4-dichloropentane then you'll have to follow the numbering based off the "parent" 1-chloropentane.

CH₃-CHCl-CH₂-CH₂-CH₂-Cl = 1,4-dichloropentane


The molecule you wrote out is actually 1,5-dichloropentane. This is because one of the chlorines, in this case it's irrelevant which, is your first position and counting out to the next one it's on the fifth carbon.

Cl-CH₂-CH₂-CH₂-CH₂-CH₂-Cl = 1,5-dichloropentane



I hope this clears up any confusion. If I misunderstood your question let me know.

[Hunter2]

My question is why is it not ClCH2CH2CH2CH2CH2Cl. If it is 1,4 dichloropentane, I do not understand why the Cl atom is not bonded to the first carbon.

Because this is 1,5-Dichloropentane

[discodermolide]

My question is why is it not ClCH2CH2CH2CH2CH2Cl. If it is 1,4 dichloropentane, I do not understand why the Cl atom is not bonded to the first carbon.

The chlorine is bonded to the first C atom. Look at the drawing I provided.