Theoretical Investigation on the Effect of Different Nitrogen Donors on Intramolecular Se⋅⋅⋅N Interactions

The effect of different donor nitrogen atoms on the strength and nature of intramolecular Se ⋅⋅⋅ N interactions is evaluated for organoselenium compounds having N , N ‐dimethylaminomethyl (dime), oxazoline (oxa) and pyridyl (py) substituents. Quantum chemical calculations on three series of compounds [2‐(dime)C 6 H 4 SeX ( 1 a – g ), 2‐(oxa)C 6 H 4 SeX ( 2 a – g ), 2‐(py)C 6 H 4 SeX ( 3 a – g ); X=Cl, Br, OH, CN, SPh, SePh, CH 3 ] at the B3LYP/6‐31G(d) level show that the stability of different conformers depends on the strength of intramolecular nonbonded Se ⋅⋅⋅ N interactions. Natural bond orbital (NBO), NBO deletion and atoms in molecules (AIM) analyses suggest that the nature of the Se ⋅⋅⋅ N interaction is predominantly covalent and involves nN→σ* SeX orbital interaction. In the three series of compounds, the strength of the Se ⋅⋅⋅ N interaction decreases in the order 3 > 2 > 1 for a particular X, and it decreases in the order Cl>Br>OH>SPh≈CN≈SePh>CH 3 for all the three series 1 – 3 . However, further analyses suggest that the differences in strength of Se ⋅⋅⋅ N interaction in 1 – 3 is predominantly determined by the distance between the Se and N atoms, which in turn is an outcome of specific structures of 1 , 2 and 3 , and the nature of the donor nitrogen atoms involved has very little effect on the strength of Se ⋅⋅⋅ N interaction. It is also observed that Se ⋅⋅⋅ N interaction becomes stronger in polar solvents such as CHCl 3 , as indicated by the shorter r Se ⋅⋅⋅ N and higher E Se ⋅⋅⋅ N values in CHCl 3 compared to those observed in the gas phase.