Question

Question #4f738

Answer 1

Here's what I get.

Explanation:

Backbonding is the sharing of electrons between an atomic orbital on one atom with an antibonding π* orbital on another atom.
A banana bond is a type of covalent bond with a geometry that looks like a banana.
Backbonding

You see back bonding in the formation of metal-carbonyl compounds such as Ni(CO)₄.

The vacant π orbitals in CO are about the same size as the filled metal d orbitals, so the orbital overlap allows electron density on the metal to be donated from the metal back to carbon π orbitals.

This bonding is from the metal to the ligand rather than the usual ligand to metal, and it involves π orbitals. Thus, the phenomenon is called π backbonding.

Banana Bonding

A banana bond looks something like a banana.

You see this type of bond in small-ring compounds like cyclopropane (C₃H₆) and cyclobutane (C₄H₈) and in 3- and 4-membered heterocyclic rings.

In these compounds, it is not possible for the carbon atoms to assume the normal `sp^3` bond angle of 109.5 °.

Increasing the `p` character in the C-C bonding orbitals makes it possible to reduce the bond angles to about 104 °.

Cyclobutane is a larger ring. It still has bent bonds, but the maximum orbital overlap is not as far off the C-C axis as it is in cyclopropane.