Bazı Monoazo Türevlerinin Proton-Verme Davranışları Üzerinde Teorik Bir İnceleme

Yıl 2007, Cilt: 20 Sayı: 1, 113 - 136, 30.06.2007

Cemil Öğretir

Öz

 Beş monoazo bileşiğinin asitlik sabitleri, pKa, yarı-empirik PM3 yöntemiyle hesaplanmış ve elde edilen asitlik sabitleri ile deneysel olarak elde edilmiş olanlar arasındaki uyum araştırılmıştır. Uyumun en iyi olduğu durumlar seçilerek proton-verme merkezleri ve mekanizmaları saptanmaya çalışılmıştır. Bulunan asitlik sabitleri kullanılarak keto-enol tautomerik denge sabitleri teorik olarak, KT dengeleri, hesaplanmış ve incelenen tüm monoazo bileşikler için enol formlarının daha kararlı olduğu gözlenmiştir. Birinci proton-verme iki hidroksil grubu içeren aromatik halkanın para-konumundaki protonunu vermesi, ikinci proton-verme ise aromatik halkanın orto-konumundaki fenolik hidroksil grubundan olmaktadır. Ancak diğer halkada orto konumunda hidroksil grubu içeren iki molekülün.farklı mekanizma ile proton verdiği gözlenmiştir. 

Anahtar Kelimeler

Proton-verme, yarı-empirik hesaplamalar, PM3 metodu. .

A Theoretıcal Study On Proton-Loss Behavıor Of Some Monoazo Derıvatıves

Öz

The deprotonation acidity constants, (pKa) of five monoazo derivatives were calculated by using the semi-empirical PM3 method and the obtained pKa values were compared with the experimental ones. Taking into account of the best fit results, the deprotonation centers and deprotonation patterns were determined. Using the calculated acidity constants the equlibrium constants, for keto-enol tautomerizm KT, were calculated. The evaluation of the toutomeric equlibrium constant volues revealed that the enol forms are more stable. It was observed that both deprotonation takes place on the aromatic ring which has two phenolic hydroxy groups. Whith the exception two molecules which deprotonates at phenolic hydroxy group located at ortho position of the other aromatic ring. The first deprotonation for all seems to take place at the para positioned phenolic hydroxyl group. 

Anahtar Kelimeler

Proton-donor, semi-empirical calculation

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