DFT Reactivity Descriptors and Catalysis - Vrije Universiteit Brussel
DFT Reactivity Descriptors and Catalysis - Vrije Universiteit Brussel
DFT Reactivity Descriptors and Catalysis - Vrije Universiteit Brussel
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Results for the 4T cluster (1Al, 3Si) model<br />
• rate constants 300-800K E A<br />
• 2 mechanisms consecutive* vs direct<br />
E A<br />
193 127 kJmol -1<br />
* Pre-exponential factor is higher so that at higher T the two<br />
mechanisms become competing (400K) (effect of ∆S act )<br />
Direct mechanism in line with experimental data ( no stable intermediates) <strong>and</strong> confirmed<br />
in periodic boundary calculations by Van Santen (J.Am.Chem.Soc.123, 2799(2001))<br />
• Influence of substituents: the role of activation hardness (MHP at work)<br />
∆ η = η −η<br />
Z. Zhou, R.G.Parr, J.Am.Chem.Soc, 112, 5720 (1991)<br />
react<br />
TS<br />
obtained via HOMO –LUMO gap<br />
E A (kJmol -1 ) k (400K) ∆η (activation hardness)<br />
Benzene 127.1 (4) 5.6 10 -24 0.0597 (4)<br />
Toluene o 114.2 (1) 3.6 10 -23 0.0493 (1)<br />
m 123.9 (3) 3.1 10 -24 0.0536 (3)<br />
p 117.8 (2) 2.2 10 -22 0.0499 (2)<br />
• electrondonating character of CH 3 -group shows up in E A .<br />
• E A <strong>and</strong> activation hardness match<br />
Pag.<br />
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