Conformational preferences of mono-substituted cyclohydronitrogens: A theoretical study

The conformational stability of mono-substituted six membered cyclic hydronitrogens (N6H5X) are investigated with the aid of electronic structure calculations. One or both hydrogens adjacent to the substituent bearing nitrogen move to the equatorial position to attain the global minimum depending on the electronegativity of X. For example, strongly electronegative substituent like F pushes both the adjacent hydrogens into equatorial position, whereas covalent bond forming amino group prefers both the hydrogens to be in the axial position. When chlorine is the substituent, it migrates to the other end of the ring and forms hydrogen bonds with two of the axial hydrogen atoms in that region. Natural bond orbital analysis indicates that all these phenomena are a manifestation of the anomeric effect to different degrees.