Structure and Bonding in Ethene The Pi Bond

Rule 7. Substituents containing a double bond are named alkenyl for example, ethenyl (common name, vinyl), 2-propenyl (allyl), and di-l-propenyl. 

As usual, the numbering of a substitnent chain begins at the point of attachment to the basic stem. The example in the margin constitntes an alkenol. However, we cannot incorporate both functional groups into the stem name. Therefore, the double bond is part of the substituent to the cyclooctanol. 

The carbon-carbon double bond in aUcenes has special electronic and structural features. This section reviews the hybridization of the carbon atoms in this functional group, the nature of its two bonds (a and 77), and their relative strengths. We consider ethene, the simplest of the alkenes. 

How much do the a and tt bonds each contribnte to the total donble-bond strength We know from Section 1-7 that bonds are made by overlap of orbitals and that their relative strengths depend on the effectiveness of this overlap. Therefore, we can expect overlap in a O bond to be considerably better than that in a rr bond, becanse the sp orbitals lie 

CHAPTER 11 Alkenes Infrared Spectroscopy and Mass Spectrometry 

---