Ch_322b_14.03 - levels an open shell system nonaromatic...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Huckel's Rule: The (4n + 2) ! -Electron Rule for Predicting Aromaticity : In 1931, the German physicist Erich Huckel carried out molecular orbital calculations on planar carbocycles in which each carbon has a p-orbital. His calculations showed that monocyclic systems containing (4n + 2) ! -electrons , where n = 0, 1, 2, 3..., have closed shells of ! -electrons like benzene. These systems have a single lowest bonding ! -molecular orbital followed by pairs of bonding ! -MOs. : The Huckel Formula Prediction : These closed shell ! -electron systems are predicted to be "aromatic" by the Huckel rule. : Total Number of ! -Electrons 2 6 10 14 n = 0 1 2 3 bonding MOs
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
A Second Prediction of Aromaticity A second way to evaluate aromatic systems is to inscribe a regular polygon inside a circle with one corner of the polygon at the bottom of the circle. Wherever a corner touches the circle, there is an energy level. Examples Benzene hexagon predicted energy levels a closed shell system "aromatic" Cyclooctatetraene octagon
Image of page 2
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: levels an open shell system nonaromatic Properties of Cyclooctatetraene In contrast to benzene, this nonaromatic compound is very reactive. It is a yellow liquid, bp 152 o C, that is stable at low temperatures, but polymerizes upon heating. It is slowly oxidized by air, and easily undergoes catalytic hydrogenation. Cyclooctatetraene is not planar, as required for an aromatic compound. It has a tub shape. 1.34 A o 1.48 A o The different bond lengths indicate localized bonds. Quiz 14.03 Use the polygon inside a circle to predict which of the the following species is aromatic or non-aromatic. H + H-H-solution Determine the number of ! electrons in each system. 4 2 4 6 Inscribe the polygon inside a circle and find the levels of the molecular orbitals. Then fill them, starting with the lowest energy MO. Determine if the electrons all lie in MOs that are stabilized. number of electrons 4 2 4 6 non-aromatic aromatic non-aromatic aromatic...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern