A quantum chemical and TST study of the OH hydrogen-abstraction reaction from substituted aldehydes: FCHO and ClCHO

In the present study, ab initio methods have been used to study the OH hydr ogen-abstraction reaction from two substituted aldehydes: FCHO and ClCHO. A complex mechanism in which the overall rate depends on the rates of two co mpetitive reactions, a reversible step where a reactant (or prereactive) co mplex is formed, followed by the irreversible hydrogen abstraction to form the products, is corroborated. This mechanism was previously shown to descr ibe accurately the kinetics of the OH hydrogen-abstraction reaction from fo rmaldehyde, and acetaldehyde. Classical transition state theory (TST) rate constants calculated with tunneling corrections, assuming an unsymmetrical Eckart barrier, agree very well with experimental upper bound values. Activ ation energy barriers and enthalpies of reaction hav e been estimated throu gh CCSD(T) single point calculations using MP2 geometries and frequencies a nd the 6-311++G(d,p) basis set.