Radialenes protonation

The chemical shifts of exocyclic methylene protons are very close to the calculated value of 4.65 ppm for four-, five- and six-membered rings not surprisingly the three-membered ring proves to be exceptional. There are also some differences in the effect exerted by carbonyl substitution in rings of different size and in the chemical shifts of radialenes. 

In the case of 1,3-butadiene, the chemical shifts of inner (H2, H3) protons and outer (HI, H4) is large, while in the case of cycloalkadienes (e.g. 1,3-cyclopentadiene and 1,3-cyclohexadiene), the difference is very small. It is interesting to note that in 1,3,5-cycloheptatriene, the chemical shifts of three kinds of olefinic protons are very diverse. The effect of the ring size and in the chemical shifts of radialenes was also included. 

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