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I have a difficulty in appointing cis trans isomer to an Alkene compound .

I have looked it up and drawn out a few -

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Which "point" should I look at to understand in order to allocate cis and trans ? I know it's between the first and last line . Thanks!

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closed as unclear what you're asking by airhuff, Todd Minehardt, M.A.R., jerepierre, hBy2Py May 16 '17 at 18:12

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ The last name is wrong. There is no cis/trans isomerism because the two methyl groups are identical. $\endgroup$ – Zhe May 15 '17 at 15:14
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You may think of the two lines representing the double bond like the bird's eye view on a door of a saloon: If the two wings, the one on the left of the double bond, and the one of right flap in the same direction, then the double bond is in cis-configuration. On the contrary, if the two flap in opposing directions, than the double bond is in trans-configuration.

For future reference -- taking into account the third picture shown by you -- cis and trans may be ambiguous; and triple and quadruple substituted double bonds' configuration are described only with E- or Z-configuration (cf. here). Eventually, as correctly pointed by @Zhe, in your last example, the double bond is neither E-, nor Z-configurated.

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