Chapter 1, Problem 13EQ

This is done by removing an unshared pair from each of two adjacent atoms and adding one electron pair as a second bond between the atoms. Each such operation reduces the number of electrons in the trial structure by two. Removing the unshared pairs of electrons on the carbon atoms and adding a second carbon–carbon bond gives

a structure in which there are four electrons involved in a double bond between the carbon atoms. The trial structure now contains electrons ____ and is correct.