Name: frost circle for pi orbital energies
Uploaded: 2023-04-30T10:31:15.000Z
Duration: 1 min 8 s
Channel: JoVE

Okrąg Frosta lub metoda wielokąta wpisanego to metoda graficzna oparta na regule Hückla do określania liczby i względnych energii π orbitali molekularnych układów płaskich, monocyklicznych i sprzężonych.
Okrąg Frost jest rysowany przez wpisanie wielokąta, reprezentującego związek cykliczny, wewnątrz okręgu, którego jeden z wierzchołków jest skierowany w dół.
Przecięcia, w których okrąg styka się z wielokątem, są oznaczone krótkimi poziomymi liniami reprezentującymi liczbę i względne energie π orbitali molekularnych.
Następnie przez środek okręgu rysowana jest przerywana linia pozioma, przecinająca wielokąt na pół. Linia ta reprezentuje energię uczestniczących orbitali p.
Wszystkie orbitale molekularne o energiach poniżej tej linii łączą się, te powyżej linii są antywiążące, a te na linii są orbitalami molekularnymi niewiążącymi.
Wreszcie, π elektronów są dodawane do poziomów energetycznych zgodnie z regułą Hunda i zasadą wykluczenia Pauliego.

schemat reguły hückla dla π mo: o krąg frosta

H&uuml;ckel's Rule Diagram of &pi; MOs: Frost Circle

Okrąg Frosta lub metoda wpisanego wielokąta to graficzna metoda określania względnych energii orbitali molekularnych π

Metoda koła Frosta lub metoda wielokąta wpisanego to graficzna metoda określania względnych energii orbitali molekularnych π (MO) dla związków planarnych, w pełni sprzężonych i monocyklicznych. Metodę tę po raz pierwszy opisali A. A. Frost i Boris Musulin w 1953 roku.

Okrąg Frosta konstruuje się poprzez narysowanie wielokąta, którego liczba krawędzi jest równa liczbie atomów węgla w danym układzie cyklicznym, z jednym z wierzchołków skierowanym w dół. Następnie rysowany jest okrąg obejmujący wielokąt tak, że wszystkie wierzchołki wielokąta stykają się z okręgiem. Punkty styku okręgu z wielokątem zaznaczono krótkimi poziomymi liniami, reprezentującymi poziomy energii orbitali molekularnych π.

<img alt="Figure1" src="/files/ftp_upload/12454/12454_PT-Figure_1.png" style="text-align: center; height: 250px;">

Następnie przez środek okręgu rysowana jest przerywana pozioma linia, przecinająca wielokąt na pół. Poziomy energii poniżej tej linii reprezentują orbitale molekularne wiążące, a powyżej tej linii reprezentują orbitale molekularne antywiążące. Poziomy energii na linii reprezentują niewiążące orbitale molekularne, z energią równą orbitalom p, z których powstają orbitale molekularne.

Na koniec elektrony π są dodawane do poziomów energii, zaczynając od najniższego i przesuwając się w górę. Zdegenerowane orbitale są najpierw wypełniane pojedynczym elektronem, a następnie łączone w parę z innym elektronem, jeśli jest dostępny, zgodnie z zasadą wykluczenia Pauliego i regułami Hunda.

Schemat reguły Hückla dla π MO: o krąg Frosta

Okrąg Frosta lub metoda wielokąta wpisanego to graficzna metoda określania energii względnych π orbitali molekularnych (MO) dla ...

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frost circle for pi orbital energies

The Frost circle is a graphical method for showing the relative energies of pi molecular orbitals in planar, fully conjugated, monocyclic compounds. It is also called the inscribed polygon method. A. A. Frost and Boris Musulin first described this method in 1953.

To build a Frost circle, draw a polygon with the same number of edges as the number of carbons in the cyclic system. Place one vertex pointing downward. Then draw a circle around the polygon so that every vertex touches the circle. Mark the touch points with short horizontal lines. These lines show the energy levels of the pi molecular orbitals.

Next, draw a dashed horizontal line through the center of the circle. This line divides the energy levels into bonding, non-bonding, and antibonding orbitals. Levels below the line are bonding molecular orbitals. Levels above the line are antibonding molecular orbitals. The levels on the line are non-bonding molecular orbitals, and they have the same energy as the p orbitals that form them.

Finally, place the pi electrons into the energy levels from lowest to highest. If two orbitals have the same energy, they are degenerate orbitals. Fill each degenerate orbital with one electron first, then pair the electrons if more are available. This follows Pauli’s exclusion principle and Hund’s rules.

Frost Circle for Pi Orbital Energies

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Aromatic rings follow H&amp;uuml;ckel’s rule, also called the 4n + 2 rule. This rule helps identify which unsaturated cyclic compounds are aromatic and why some ring systems are unstable instead. Benzene is the classic example, while cyclobutadiene and cyclooctatetraene show different behavior and are not aromatic. Eric H&amp;uuml;ckel, a German chemical physicist, first described the structural features needed for aromaticity. An aromatic compound must be cyclic, planar, and continuously...

h&uuml;ckel's rule diagram of &pi; mos: frost circle

The Frost circle is a graphical method for showing the relative energies of pi molecular orbitals in planar, fully conjugated, monocyclic compounds. It is also called the inscribed polygon method. A. A. Frost and Boris Musulin first described this method in 1953. To build a Frost circle, draw a polygon with the same number of edges as the number of carbons in the cyclic system. Place one vertex pointing downward. Then draw a circle around the polygon so that every vertex touches the circle.

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key terms and concepts

Learn how the Frost circle maps pi molecular orbital energies in planar conjugated rings, from drawing the polygon to filling bonding, non-bonding, and antibonding levels.

Frost Circle for Pi Orbital Energies | JoVE K12

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Frost Circle for Pi Orbital Energies

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