Name: hbr selectivity in alkene addition thermodynamics
Uploaded: 2025-05-22T09:05:43.000Z
Duration: 1 min 32 s
Channel: JoVE

Anti-Markovnikov ilavesinin sadece HBr ile gözlendiğini hatırlayın. HCl ve HI ile radikal ekleme termodinamik olarak elverişsizdir.
Ama neden?
Radikal mekanizmada yer alan her bir yayılma adımı için termodinamiği inceleyelim.
Bir reaksiyonun kendiliğinden olması için, Gibbs serbest enerjisindeki ∆G'deki değişimin negatif olması gerekir.
İlk yayılma adımı için, ∆G'nin işareti, entalpi ve entropi terimleri arasındaki rekabet tarafından belirlenir.
HBr ve HCl durumunda, entalpi terimi düşük sıcaklıklarda baskındır ve ∆G negatif hale gelir, bu da termodinamik olarak uygun bir reaksiyon anlamına gelir.
Bununla birlikte, HI durumunda, hem entalpi hem de entropi terimleri pozitiftir, bu da sıcaklıktan bağımsız olarak ∆G'nin pozitif olduğunu ve termodinamik olarak elverişsiz bir reaksiyonu gösterdiğini ima eder.
İkinci yayılma adımı için, entropi terimi sıfıra yakındır çünkü reaktanların ve ürün moleküllerinin sayısı eşittir. Yani, entalpi terimi ∆G'nin işaretini belirler.
Açıkça görüldüğü gibi, ∆G, HCl için pozitiftir ve reaksiyonu termodinamik olarak elverişsiz hale getirir.
Genel olarak, iki yayılma aşaması yalnızca HBr durumunda termodinamik olarak elverişlidir.

alkenlere radikal anti-markovnikov İlavesi: termodinamik

Radical Anti-Markovnikov Addition to Alkenes: Thermodynamics

Hidrojen halojenürlerin bir alkene anti-Markovnikov eklenmesi termodinamik olarak yalnızca HBr ile mümkündür. HCl ve HI gibi diğer hidrojen halojenürlerle radikal katılma reaksiyonu termodinamik olarak elverişsizdir.

<img alt="Figure1" src="/files/ftp_upload/12904/12904_PT_Figure_1.svg" style="text-align: center; height: 125px;">

Termodinamik faktörler

Sıcaklık, bir reaksiyonun kendiliğindenliğini etkiler ve bu, Gibbs serbest enerjisindeki (ΔG) değişime dayalı olarak değerlendirilebilir. Gibbs serbest enerjisindeki ΔG değişimi negatifse reaksiyon kendiliğinden gerçekleşir. Aşağıda gösterildiği gibi, ΔG doğrudan iki terimin (ΔH ve −TΔS) değerlerinden değerlendirilebilir.

<img alt="Figure2" src="/files/ftp_upload/12904/12904_PT_Figure_2.svg" style="text-align: center; height: 14px;">

HBr ile anti-Markovnikov ilavesinin termodinamik fizibilitesi, radikal mekanizmada yer alan her yayılma adımından tahmin edilebilir.

Radikal reaksiyonun ilk yayılma adımında ∆G işareti, entalpi ve entropi terimleri arasındaki rekabetle belirlenir. Daha düşük sıcaklıklarda, HBr ve HCl ile radikal eklenmesi entalpi terimine hakimdir. Sonuç olarak ΔG'nin negatif olması reaksiyonun termodinamik olarak uygun olduğunu gösterir. Ancak yüksek sıcaklıklarda reaksiyon endotermiktir ve termodinamik açıdan uygun değildir. Bunun aksine, HI ile sıcaklıktan bağımsız olarak hem entalpi hem de entropi terimleri pozitiftir. Sonuç olarak ∆G pozitif hale gelir, bu da reaksiyonun termodinamik olarak uygun olmadığını gösterir.

İkinci yayılma adımında, reaktanların ve ürün moleküllerinin sayısı eşit olduğundan entropi terimi sıfıra yakındır, bu da ∆G işaretinin entalpi terimine bağlı olduğu anlamına gelir. HBr ve HI için entalpi terimi baskın olduğundan reaksiyon ekzotermiktir ve termodinamik olarak uygundur. Ancak HCl ile ∆G pozitiftir, yani reaksiyonun endotermik ve termodinamik olarak uygun olmadığı anlamına gelir.

Özetle, reaksiyondaki iki yayılma adımı yalnızca HBr için termodinamik açıdan uygundur.

Alkenlere Radikal Anti-Markovnikov İlavesi: Termodinamik

Hidrojen halojenürlerin bir alkene anti-Markovnikov ilavesi termodinamik olarak sadece HBr ile mümkündür. Diğerleri ile radikal ekleme reaksiyonu ...

radical-anti-markovnikov-addition-to-alkenes-thermodynamics

Education

JoVE Core

Organic Chemistry

Organik Kimya

Unit 1

Ünite 1

Radical Chemistry

Radikal Kimya

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

hbr selectivity in alkene addition thermodynamics

Anti-Markovnikov addition of hydrogen halides to alkenes depends on thermodynamics. In this radical reaction, only HBr makes the overall process feasible. With HCl and HI, the same addition is thermodynamically unfavorable.

Temperature affects whether the reaction is spontaneous. Spontaneity is measured with Gibbs free energy, or ΔG. When ΔG is negative, the reaction can occur on its own. ΔG is determined by two terms: ΔH, which is the enthalpy change, and −TΔS, which is the entropy term.

The first propagation step depends on the balance between enthalpy and entropy. At lower temperatures, radical addition with HBr and HCl is driven by the enthalpy term, so ΔG is negative and the step is favorable. At higher temperatures, the reaction becomes endothermic and thermodynamically unfavorable. With HI, both the enthalpy and entropy terms are positive at any temperature, so ΔG stays positive.

The second propagation step is different because the number of reactant and product molecules is equal. That makes the entropy term close to zero, so ΔG depends mainly on enthalpy. For HBr and HI, the enthalpy term makes the step exothermic and favorable. For HCl, ΔG is positive, so the step is endothermic and unfavorable. Taken together, both propagation steps are thermodynamically favorable only with HBr.

HBr Selectivity in Alkene Addition Thermodynamics

hbr-selectivity-in-alkene-addition-thermodynamics

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key terms and concepts

See why anti-Markovnikov addition to alkenes is thermodynamically favorable only with HBr, and how ΔG, enthalpy, entropy, and temperature affect each step.

HBr Selectivity in Alkene Addition Thermodynamics | JoVE K12

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JoVE Core Organik Kimya, kısa ve anlaşılması kolay animasyonlu video dersleri kullanarak stereokimya, reaksiyonlar ve mekanizmaların temel kavramlarını açıklar. Buna ek olarak, bilim insanlarının yer aldığı videolar, ilgili kavramların günümüz laboratuvarlarında gerçekleştirilen klasik ve orijinal araştırma deneylerinde nasıl uygulandığını göstermektedir.

HBr Selectivity in Alkene Addition Thermodynamics

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