Cylindrical symmetry

[Mrudula Akkinepally]

In lecture 22, Dr. Lavelle says that sigma bonds are characterized by electron density with cylindrical symmetry and I was wondering if someone could illustrate what that means. Thank you!

[Hannah_Kim_1I]

I believe that just means that when each of the s orbitals are bonded, they create a sort of cylindrical shape.

[Marcus Lagman 2A]

Hello!

Adding onto what is said before this post, the cylindrical symmetry of sigma bonds allows the bond to be rotated any number of degrees due to bonding orbitals only meeting end to end. This is why sigma bonds are considered to be freer and less restrictive than pi bonds since pi bonds lack cylindrical symmetry.

I hope this helps!

[Nathan Tong 3G]

I believe that what Dr. Lavelle means by this is that the electron density is symmetric around the bond axis, and rotating it around this axis would not change how it looks. The pi bond on the other hand, does not have this kind of symmetry, because it overlaps side-by-side rather than head-to-head.

[Neel Sharma 3F]

Cylindrical symmetry in regard to sigma bonds is in relation to the symmetry of the electron density bonding regions relative to the internuclear axis. Regardless of the type of bond, s-s, s-p, p-p, the bonds are always cylindrically symmetrical. The diagrams on the lecture slides are helpful. Hope this helps!