Why can alkynes have cis and trans isomers?

1 Answer
anor277
Feb 13, 2016

Alkynes cannot exhibit cis / trans isomerism.

Explanation:

An alkyne linkage is linear: #R-C-=C-R'#; geometric isomerism across the triple bond cannot be supported. On the other hand, a suitably substituted olefin, #R_1R_2C=CR_3R_4#, can support such isomerism, as can suitably substituted cyclic structures. In each of the cases, the connectivity of each isomer is the same. #C1# is connected to #C2#, is connected to #C3# etc. but the spatial orientation, the geometry, is different.

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