Name: benzene π orbitals and electron delocalization
Uploaded: 2025-05-22T09:05:38.000Z
Duration: 1 min 18 s
Channel: JoVE

Moleküler orbital model, benzeni altı sp2 hibritleştirilmiş karbon içeren düzenli bir düzlemsel altıgen olarak tanımlar.
Bitişik karbon atomları, sp2–sp2 orbital örtüşmesi yoluyla σ bağlar oluşturur. Her karbon atomu ayrıca sp2-1 s orbital örtüşme ile hidrojen ile bir σ bağı oluşturur. Tüm yapıştırma açıları 120°'dir.
Ek olarak, her bir karbon, halkanın düzlemine dik olan yarı dolu hibritlenmemiş 2p atomik orbitaline sahiptir.
Bu altı 2p orbitali, üç bağ ve üç antibağ moleküler orbital oluşturmak üzere birleşir.
Bağ orbitalleri, altı π elektron tarafından tamamen doldurulurken, antibonding orbitalleri boştur ve benzene stabilite sağlayan kapalı bir kabuk konfigürasyonu verir.
Sonuç olarak, π elektron yoğunluğu, halka düzleminin üstünde ve altında halka şeklindeki bölgeler şeklinde delokalize edilir.
Delokalizasyon ayrıca, tipik karbon-karbon tek ve çift bağ uzunlukları arasında bir değere sahip benzen için neden sadece bir karbon-karbon bağ uzunluğunun gözlendiğini de açıklar.

benzenin yapısı: moleküler orbital model

Structure of Benzene: Molecular Orbital Model

Moleküler yörünge (MO) modeline göre benzen, altı sp^2 hibritleştirilmiş karbondan oluşan düzenli bir altıgen içeren düzlemsel bir yapıya sahiptir. Şekil 1'de gösterildiği gibi, her karbon, 120°'lik C–C–C ve H–C–C bağ açılarıyla diğer üç atoma bağlanır. C-H bağ uzunluğu 109 pm'dir ve C-C bağ uzunluğu 139 pm'dir; bu, sp^3 hibritlenmiş karbonların (154 pm) ve sp^2 hibritlenmiş karbonların (133 pm) tekli bağ uzunluğunun ortasındadır.

<img alt="Figure1" src="/files/ftp_upload/12451/12451_PT_Figure_1.svg" style="text-align: center; height: 190px;">

Karbon atomları ayrıca, halka düzlemine dik olan, komşu karbonların p yörüngeleri ile örtüşen ve halka düzleminin üstünde ve altında sürekli bir π elektron döngüsü oluşturan, bir elektronlu, hibritleşmemiş bir 2p atomik yörüngeye sahiptir. Moleküler yörünge (MO) teorisine göre, bu altı 2p yörüngesi birleşerek aşağıdaki şekilde gösterildiği gibi altı adet π siklik moleküler yörünge (MO) ψ_1, ψ_2, ψ_3, ψ_4, ψ_5 ve ψ_6 oluşturur. Bunlar arasında ψ_1, ψ_2 ve ψ_3 bağ oluşturan MO'lardır; ψ_4, ψ_5 ve ψ_6 ise bağönler MO'lardır. Genellikle MO'ların enerjisi ve düğüm sayısı ψ_1'den ψ_6'ya artarken bağlanma etkileşimi azalır. Ancak siklo sistemlerin bu MO'ları, iki dejenere MO'ya sahip olmaları nedeniyle 1,3-bütadien gibi doğrusal sistemlerden farklılık gösterir.

<img alt="Figure2" src="/files/ftp_upload/12451/12451_PT_Figure_2.svg" style="text-align: center; height: 250px;">

En düşük enerjili bağ MO, ψ_1'in, tüm yörüngelerin aynı fazda olduğu düğümleri yoktur. Bir sonraki en düşük MO'nun bir düğümü vardır ve düğüm düzleminin bir bağdan veya bir atomdan geçtiği iki şekilde temsil edilebilir. Bu iki bağlanma MO'su dejeneredir ve ψ_2 ve ψ_3 olarak temsil edilir. Benzer şekilde, iki düğüm düzlemi bağlardan veya atomlardan geçerek ψ_4 ve ψ_5'lik iki dejenere bağönler MO'su sağlayabilir. Son MO, ψ_6, tüm p yörüngelerinin faz dışı kombinasyonunu temsil eden üç düğüm düzlemi ile en yüksek enerjiye sahiptir.

Halka düzleminin üstünde ve altında delokalize π elektron yoğunluğunun kapalı bir kabuğunu oluşturan altı π elektronu, enerjileri izole edilmiş p yörüngesinden daha düşük olan üç bağlayıcı MO'yu (ψ_1, ψ_2 ve ψ_3) işgal eder, dolayısıyla benzenin alışılmadık kararlılığı.

Benzenin Yapısı: Moleküler Orbital Model

Moleküler orbital (MO) modeline göre, benzen, altı sp2 hibritleştirilmiş karbondan oluşan düzenli bir altıgen ile düzlemsel bir yapıya sahiptir. Şekil 1'de gösterildiği gibi, ...

structure-of-benzene-molecular-orbital-model

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benzene π orbitals and electron delocalization

Benzene has a planar ring structure with delocalized π electrons. Its six carbon atoms form a regular hexagon, and each carbon is sp2 hybridized. The C–C–C and H–C–C bond angles are 120°, which matches the flat shape of the ring.

Each carbon is bonded to three other atoms. The C–H bond length is 109 pm, and the C–C bond length is 139 pm. That C–C distance is midway between the single bond length of sp3 hybridized carbons, 154 pm, and the sp2 value, 133 pm.

Beneath and above the ring plane, each carbon also has one unhybridized 2p atomic orbital with one electron. These p orbitals stand perpendicular to the ring and overlap with neighboring p orbitals. Together, they form a continuous loop of π electron density above and below the ring.

In molecular orbital theory, the six 2p orbitals combine to make six cyclic π molecular orbitals: ψ1, ψ2, ψ3, ψ4, ψ5, and ψ6. The first three, ψ1 through ψ3, are bonding molecular orbitals. The last three, ψ4 through ψ6, are antibonding molecular orbitals.

The energy of the molecular orbitals rises from ψ1 to ψ6, and the number of nodes also increases. As the nodes increase, the bonding interaction decreases. Cyclic systems differ from linear systems such as 1,3-butadiene because they have two degenerate molecular orbitals, or orbitals with the same energy.

The lowest-energy bonding orbital, ψ1, has no nodes and places all orbitals in phase. The next bonding level has one node and can be drawn in two ways, with the nodal plane passing through a bond or through an atom. These two orbitals are degenerate and are labeled ψ2 and ψ3.

The same idea applies to the antibonding set. Two nodal planes can pass through bonds or atoms, giving two degenerate antibonding orbitals, ψ4 and ψ5. The final orbital, ψ6, has the highest energy and three nodal planes. It represents the out-of-phase combination of all p orbitals.

Benzene has six π electrons, and they occupy the three bonding orbitals, ψ1, ψ2, and ψ3. This creates a closed shell of delocalized π electron density above and below the ring. Because these electrons are in orbitals lower in energy than an isolated p orbital, benzene shows unusual stability.

Benzene π Orbitals and Electron Delocalization

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Explore benzene’s planar ring, sp2 carbons, and six π molecular orbitals. Learn how delocalized electrons and bonding orbitals give benzene its stability.

Benzene π Orbitals and Electron Delocalization | JoVE K12

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Benzene π Orbitals and Electron Delocalization

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