Solvent dependence of rotational energetics and formyl-proton long-range spin-spin coupling behavior of 2,6-dichloro- and 2,6-dinitrobenzaldehydes using dipolar couplings and temperature dependence of long-range couplings

Abstract

The formyl rotational energetics, solvent effects on the energetics and formyl-proton spin-spin coupling behavior of 2,6-dichlorobenzaldehyde were studied by using dipolar couplings analysis and the temperature dependence of the spin-spin couplings. The general form of the rotational potential was taken from molecular mechanics and the conjugative sin2 Θ-type component (where Θ is the formyl-ring dihedral angle) was then optimized using the dipolar couplings obtained by analyzing 1H NMR and 13C proton satellite spectra in a liquid crystal solvent. The optimization based on the dipolar couplings gave the following rotational free energy potential: V(Θ) = 4.5 cos6 Θ + 10.7 (± 2.0) sin2 Θ, in kJ/mol. The analysis based on the temperature dependence of 6J data allowed estimation of solvent effects on the potential. For example, the potentials in acetone and in acetonitrile differ by a 1.0 sin2 2Θ (in kJ/mol). The chloroform solvent effect can be described by term of -1.0 cos6 Θ. When the formyl-proton six-bond coupling data was fit, assuming it obeyed the expression 6J(Θ) = 6J90 sin2 Θ + 6J0 and assuming 6J0 = 0.015 Hz, the analysis yielded 6J90 of -0.48 (± 0.03) Hz. The scalar coupling temperature dependence method was applied also to the conformational analysis of 2,6-dinitrobenzaldehyde.Key words: spin-spin coupling, dipolar coupling, solvent effect, rotational barrier, benzaldehyde.

1H NMR spectral analysis and conformational behavior of n‐alkanes in different chemical environments

“…It is obvious that for longer alkane chains, the effect that favors the t n conformations is more significant and can be termed a collaborative interaction between t n conformations. These observed solvent effects can be classified as packing effects, and their orders of magnitude are about the same (maximum 0.5 kJ/rotating bond), which we have reported before …”

“…These observed solvent effects can be classified as packing effects, and their orders of magnitude are about the same (maximum 0.5 kJ/rotating bond), which we have reported before. [26] Comment on approximate analysis of n-alkane spectra When the number of the spin particles is larger than five, the accurate quantum mechanical simulation of the signals is computationally slow, and the spectral analysis time increases. In addition, the information from the small 5 J and 6 J coupling constants cannot be obtained unambiguously.…”