No abstract

No abstract

An investigation employing the semiempirical molecular orbital MNDO method in the program package of the HyperChem 7.5 software to calculate ΔH f (M), ΔH f [M+H] + and local proton affinities (PAs) as well as the charge distributions for the two highly electronegative hetero atoms (O 11 and N 1) in six quinolone derivatives have been undertaken. The MNDO calculated values of PAs for the quinolone derivatives at site O 11 and at site N 1 indicate that the average energy separation between PA values at two respective sites is equal to about 164 kJ.mol-1. This allows the authors to conclude that the protonation at site O 11 is a more favoured process than at N 1. This conclusion can be explained as resulting from the presence of unsaturated carbonyl (C ═ O) double bond and ion pair electrons of the oxygen atom, which increase the influences of the protonation at O 11 site, which is known to be a good proton acceptor. The preferential protonation at site O 11 for the studied molecules have been confirmed by the calculated ΔH f [M+H] + values at sites O 11 and N 1 .

No abstract