The ratio of the two tautomers is d

The ratio of the two tautomers is described by the equilibrium constant KT, (Eq.3). The computed absolute values of
KT >> 1 show a large preference for the keto tautomer relative to the enol one (Table 4). In the vapor state, the
highest stability is exhibited by the keto tautomer of cathinone. However, the absolute value of KT strongly depends
on the accuracy of the evaluation of the free energy. Table 4 contained the pKT of the equilibrium constants
calculated from the relation (4). Some pKT were low or high; that determinate the privileged direction of
equilibrium. If the pKT was high, equilibrium moved from right towards the left and when it was low, equilibrium
moved from left towards the right. By taking account of all these directions of displacement, we obtained the Keto –enol (Z) isomer is 1.0428 and Keto – enol (E) 3.1244, which proved to be the enol (Z) is more stable, which explain,
intramolecular hydrogen bond generates a five ring member ring. The intramolecular hydrogen bonding is between
O8-H17 donor and N11 acceptor of the enol (Z) isomer, but in case of the enol (E) no intramolecular hydrogen bond
generate.
The magnitude of the dipole moment is strongly related to the tautomeric stability. The calculated dipole moments
of the studied tautomers are listed in Tables 3. The dipole moment values for keto, enol (Z) and enol (E) are 3.0197,
2.3517 and 1.6852 respectively at the B3LYP level. In the gas phase, the highest value of dipole moment is found in
case of keto while the lowest dipolar one is enol(E) .The dipole moment order in gas phase is keto > enol(Z) >
enol(E).