Ab initio study of anionic oxy – cope , thioxy- cope and seloxy-cope rearrangements

In this work ,ab initio quantum mechanic method (B3LYP/6-311++G**) was used to investigate the impact of the electronic resonance on the cope rearrangement reaction in hexa- 1,5- diene- 3- olate (1) , hexa- 1,5- diene- 3 thiolate(2) and hexa- 1,5- diene-3- selenolate (3) . B3LYP/6-311++G** results show that the energy barrier of the cope rearrangement reaction decreases fromcomound1 to compound 3 . Also, the NMR results obtained showed that the calculated NICS(0) values of the chair like transition state structures containing axial O- , S- and Se- groups are -14.7851 , -8.5457 and -5.5876 ppm , respectively. The calculated NICS(0) values for the chair like transision state structures containing equatorial O- , S- and Se- groups are -15.0750 , -14,1705 and 7.8536 ppm , respectively . Based on the NMR results obtained , NICS(0) increases from the transistion state structure of compound 1 to compound 3 . This fact explains the decrease of the aromatic character from the transition state structure of compound 1 to compound 3 . Accordingly , based on the results obtained from this work , the decrease of the aromatic character of the transition structures increases their corresponding energies and increases the cope rearrangement barrier heights from compound 1 to compound 3