The 38th member of the Cahn-Ingold-Prelog system, cumulene is a horizontal ringed cyclic structure composed entirely of carbon atoms. It is unique in that it has no double bonds and can be seen as a “carbon with zero bond angle”.
H−C−H Bond Angles
In cumulene, what are the c=c=c and h−c−h bond angles, respectively?
I will give two numerical values for each for this question. The first number is in degrees and then the second number will be given as an angle whose tangent is 1/2. For instance, 2π/4 would be 45°. The reason for this approach is to make the numbers more manageable.
“Interpretation:” Please use the definitions that I provided in my previous response to this question. They can be found here: http://www.chemistrydiscussion.com/topic/1392-cumulene
“Numerical values:” I was able to find some value of h−c−h bond angles using a very accurate calculation written by Douglas F. Bonnett (see link below). Analysis of his results shows that 4π/2 is equivalent to 3.21 and 2π/4 is equivalent to 45° (that equates to 1/2(1+tan−1(−1))).
“Conclusion:” There are not so many organic compounds that contain only one double bond to carbon and are non-fragmented. So cumulene, H−C=C, is an extremely rare molecule. It was mainly found in natural sources and there highly improbable that it will be found in a laboratory.
Possible links to helpful sites:
I provided some links for the reader to locate the definition of bond angles and for the location of data required to solve this problem. The first link (http://www.chemistrydiscussion.com/topic/1392-cumulene) contains my response from when I asked this exact same question earlier in this forum. The second link (http://en.wikipedia.org/wiki/Cumulene) is a link to Wikipedia where I found some data. The third link (http://www.bonnett.com/chemistry_data/cahn-ingold-prelog-systems-cumulenes/) is a link to a page containing an article written by Douglas F. Bonnett in which he calculated the values of the angles at high and low temperature of various Cahn Inggold Prelog C-H bonds using NMR techniques.
“1.” Douglas F. Bonnett, Journal of Chemical Physics, Volume 73, Issue 7, pp 2766-2769, 1981
“2. The Wikipedia page for bond angles in organic compounds (http://en.wikipedia.org/wiki/Bond_angle)
“3. The Wikipedia page for cumulene (http://en.wikipedia.org/wiki/Cumulene)
“4. The Wikipedia page for Cahn-Ingold-Prelog (http://en.wikipedia.org/wiki/Cahn-Ingold-Prelog)
“5. Douglas F. Bonnett’s Journal of Chemical Physics article (http://www.bonnett.com/chemistry_data/cahn-ingold-prelog-systems-cumulenes/)
“6. (Part of) the Wikipedia page on ring spectra (http://en.wikipedia.org/wiki/Ring_spectrum)
“7. Angles of Cahn Inggold Prelog C−H bond angles “(“an analysis of experimental and theoretical Cien Ullmann, A., Canfield, J., and Prelog, P. data on cyclic cumulenes, cyclopropanes, and 1-cyclohexenecumulene.”)
Middle States Association of Colleges and Schools “Commission on Higher Education” website: http://www.msche.org/
E-mail address for David Bressoud: brasoud@hunter.cuny.edu
E-mail address for the editor: hjstemp@gmail.com
The category that this response will be placed in the Science Discussion Forum under is as follows: Although I had another question about cumulene, there were some uncertainties in it and I decided to ask something simpler to be able to understand my results better, like here (http://www.chemistrydiscussion.com/topic/1392-cumulene) (I just copied the title). The following information was given as required: Name, School, Degree, Student ID Number, Class Standing Appropriate HIGHER LEVEL:
I am a senior chemistry student at Hunter College who will be graduating in May. I came across your site while looking for information on cumulene. I am writing a paper for my organic chemistry class on the topic of cumulene and I came across your website. I would be most appreciative if you could take a look at my paper and respond to it, e-mail me back if you wish. My paper is available here: http://www.scribd.com/doc/7534061/Potential-Nuclear-Bonding-in-Cumulene
This paper was written by Jose Cruz, Jr. He is a senior chemistry student at Hunter College.
The year this paper was written was 2010.
I am interested in the ways that chemical bonds can be classified in terms of their symmetry and stereochemistry. I am also interested in the energy levels of molecular orbitals and how they relate to bond formation and stability.” “Abstract: The Lewis structure for H−C−H clearly shows that it has a single bond between hydrogen and carbon.
