[lexi105]

I'm not sure that I have explained this through enough for understanding.

Geometric isomers exist in the alkenes but not in the alkynes. Explain why.

A geometric isomer is a rigid C = C double bond that can be found amongst the alkenes. It is found in the alkenes and not the alkynes because in the alkenes contain atleast 1double bonds whereas the alkynes contain atleast 1 triple bond. In alkenes there are four distinct positions where different molecules or groups can be. Switching the position of the two groups whether cis (opposite sides) or trans (across) will form a geometric isomer. However, in alkynes there are not two groups to switch, due to the triple bonding, which restricts them from having four extra bonds.

Thanks!

[AWK]

Discuss angles between substituents in sp2 and sp hybridization

[Dan]

A geometric isomer is a rigid C = C double bond that can be found amongst the alkenes.

No, a geometric isomer is not a bond!

http://en.wikipedia.org/wiki/Geometric_isomerism