Question

Number of \[\pi \]- electrons in cyclobutadienyl anion ${{\text{(}{{\text{C}}_{4}}{{\text{H}}_{4}})}^{-2}}$ is:
(A) 2
(B) 4
(C) 6
(D) 8

Answer 1

Hint: For this problem, we have to understand the concept of pi - electrons first. And then we have to draw the proper diagram of cyclobutadienyl through which can easily count the total number of pi - electrons.

Complete step by step solution:
-In the given question we have to calculate the total number of pi - electrons which are present in the cyclobutadienyl anion.
-So, firstly we should know about the pi - electrons. As we know that two kinds of electrons are sigma and pi electrons.
-So, pi electrons are the type of electrons which are present in the pi - bond such as double and triple bond whereas sigma electrons are found in sigma bonds such as a single bond.
-Now, to calculate the total number of pi - electrons firstly we have to draw the structure of cyclobutadienyl anion that is:

-So, as we can see there is one double bond which means 2 pi electrons because we know that the one bond consists of two electrons and along with it two negative charges are also present.
-We know that each charge consists of a total of two electrons so a total of 4 pi - electrons will be present.
-Thus, there are a total of 6 pi - electrons present in cyclobutadienyl anion.
-And a total of 4 sigma bonds or 8 sigma electrons are present in the cyclobutadienyl anion.

Therefore, option (C) is the correct answer.

Note: The sigma and pi bond are different from each other due to the different types of overlapping because the sigma bond is formed from the head-on overlapping whereas pi bond is formed from lateral overlapping.