What are the most number of consecutive double bonds carbon can have

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Discussion Overview

The discussion revolves around the maximum number of consecutive double bonds that carbon can have, exploring the implications of nomenclature, molecular structure, and potential limits. It includes theoretical considerations and references to specific molecular examples.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • Some participants mention the existence of various types of compounds with consecutive double bonds, such as dienes, trienes, and allenes, and question what limits their length.
  • One participant suggests that extremely long polymers of acetylene can exhibit this structure without specific end groups, referencing polyacetylene as an example.
  • Another participant argues that there is no inherent limit to the length of 'ene' structures and highlights the significance of conjugated systems in producing color, noting that the type of double bond can vary.
  • A participant raises a question about the geometry of allene and the configuration of carbon atoms in terms of pi molecular orbitals, seeking clarification on the bonding interactions between adjacent carbons.

Areas of Agreement / Disagreement

Participants express differing views on the limits of consecutive double bonds, with some suggesting no limits while others imply potential structural constraints. The discussion remains unresolved regarding the specifics of these limits and the implications of molecular geometry.

Contextual Notes

There are unresolved questions regarding the geometry and bonding interactions in molecules with consecutive double bonds, particularly in relation to allene structures and conjugation.

bananan
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as there are dienes, trienes, qua-enes, etc. allenes

and what limits it or prevents it from continuing on.

i.e
c=c
c=c=c diene
c=c=c=c triene-enes
(c=c=c=c=c=c=c=c)n

with each end "capped" by a -CN
 
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Longer than I think nomenclature could easily describe. Extremely long polymers of acetylene have this structure without the cyano caps of course.

You can read more here,

http://en.wikipedia.org/wiki/Polyacetylene
 
There is no limit to 'ene' length. One point of interest is that alternating 'enes' and 'anes' (aka, C=C-C=C-C=C) called conjugated 'enes' are the molecular basis for producing color. The longer the conjugated molecule is, the longer the wavelength of its emitted light. Of course, the doulbe bond doesn't have to be C=C, it could be C=N or C=x, as long as the molecule is conjugated.
 
bananan, you may want to understand the actual geometry of an allene.

http://wps.prenhall.com/wps/media/o..._Resources/Chapter_08/Text_Images/FG08_01.JPG

How would the carbon on the right be configured in terms of pi molecular orbitals to arrange for the second bond? Would this second pi molecular be uniquely bonded to the next adjacent carbon on the right, or would it also have some interaction with the carbon on the left?
 

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