Can someone break down the steps for naming $\ce{CH3-C(Cl)=C(Cl)-CH2-CH3}$?

enter image description here

  • $\begingroup$ I redrawn your structure using free LaTeX package chemfig based on your comment and previous attempt to format it using source code markup tool. There are also numerous free GUI tools such as MarvinSketch to draw molecules if you cannot reach the wanted representation with ASCII graphics (which is understandable). $\endgroup$
    – andselisk
    Jul 23 '19 at 4:16
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    $\begingroup$ Also, for the reference, see How to ask and answer nomenclature questions?. I think there is a very similar question asked before, but I'm unable to find it for now; probably other users could help. $\endgroup$
    – andselisk
    Jul 23 '19 at 4:18



The longest carbon chain is a 5 membered chain with a carbon-carbon double bond. Since double bond must be given the least locant, we number it from the leftmost carbon as in your image. The substituents are named accordingly by indicating their positions.

For the stereochemistry aspect of the compound, we observe the following:

The highest priority group on the second carbon atom from the left, as per the Cahn–Ingold–Prelog priority rule is the chlorine atom, and on the third carbon atom from the left it is again chlorine. Clearly, both the higher priority groups (here chlorine atom) are opposite, and so the configuration is E. To learn about E-Z notation click here.

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    $\begingroup$ (E)-2,3-dichloropent-2-ene? $\endgroup$
    – PCK
    Aug 1 '19 at 10:54
  • $\begingroup$ It would be best to edit your answer to actually contain the correct answer. Please also see our guidelines on how to ask and answer nomenclature questions. $\endgroup$ Sep 3 '19 at 12:25
  • $\begingroup$ @Martin-マーチン, Could you please tell whether the answer is fine now. I have improved the answer to my best. This was my first attempt in answering. $\endgroup$
    – Vishnu
    Sep 3 '19 at 16:01

1-2 dichloro pent-2-ene

As per the rule:

  1. Longest carbon chain is to be considered.
  2. Numbering of carbon should start from the side which has lowest set of locants i.e from right side, locants are 3,4 and from left side, locants are 2,3.

So answer is 2-3-dichloro pent-2-ene.

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    $\begingroup$ I'm afraid without a the stereodescriptor this answer is incomplete. It would also benefit from a better formatting, i.e. correct spelling and punctuation, as well as an correctly rotated image. $\endgroup$ Sep 3 '19 at 12:21

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