What is conjugation in alkenes?
“The phenomenon of the existence of alternate double and single bonds among carbon atoms is called conjugation.”
Example of Conjugated Compound:
e.g. 1,3-butadiene CH2 = CH – CH = CH2 is a conjugated compound. In it all the four carbons are sp2 hybridized. Also, all carbons and hydrogens in this compound are in the same plane. All four carbons have an unhybridized p-orbital which is perpendicular to the plane of δ-bonds. The p-orbitals of carbon 2 and 3 overlap on either side so π-electrons are not restricted to two carbons rather they are attracted by all the four carbons. Thus delocalized π-bonds are formed in such conjugated compounds.
The delocalization of π-electrons is responsible for the greater stability of 1,3-butadiene. The C – C single bond length is 1.48Ao which is shorter than the normal C – C single bond length (1.54 Ao). Similarly, C = C double bond length is 1.37 Ao which is longer than normal C = C double bond (1.34Ao).