Hydroacridines: Part 33. An experimental and DFT study of the ¹³C NMR chemical shifts of the nitrosamines derived from the six stereoisomers of tetradecahydroacridine

Abstract

The paper presents the experimental and DFT-calculated values of the 13 C NMR chemical shifts of the six stereoisomers of tetradecahydroacridine and of the corresponding nitrosamines. Performing the DFT calculations using several combinations of functional and basis sets, it was found that the best experimental-calculated agreement was obtained for OPBE/6-311++G (dp) method. Considering the effect of N-nitrosation upon the 13 C NMR chemical shifts of the C-α carbons of secondary amines, it was found that if following nitrosation both C-α carbons are shifted upfield or both are shifted downfield, then the resulted nitrosamine will have a sterically strained ─N═O group. If, however, one of the C-α is shifted upfield and the other is shifted downfield, then the ─N═O group will be strain-free or weakly strained. Our calculations predict strain energies of about 10-15 kcal mol −1 in the first case and ≈0-6 kcal mol −1 in the latter.

DFT Approach for Predicting 13C NMR Shifts of Atoms Directly Coordinated to Nickel

“…NMR chemical shifts (CSs) of the ligand nuclei directly involved in coordination with the metal dramatically depend on the coordination type and carry information on the molecular and electronic structure. − Therefore, the calculations of NMR CSs of coordinated atoms for tentative structures and comparison with experimental data are promising for obtaining accurate information on the molecular and electronic structure. While the quantum chemical calculation of 13 C, 15 N, and 31 P chemical shifts for main-group compounds has reached a remarkable level of accuracy, − there are fewer reports for compounds including transition metals (TMs). ,− There are several reasons for this: electron correlation is especially important for transition metal (TM) complexes, , it is believed that relativistic effects may be important, particularly for 4d and 5d metals, ,,− ,− and exchange between a variety of structural forms with low transition barriers and medium effects may complicate the situation.…”

NMR “Finger Prints” of N-Heterocyclic Carbenes, DFT Analysis: Scopes and Limitations

“…On the other hand, in recent years there has been huge progress in methods of nonempirical estimation of NMR parameters. Particularly notable are advances in CS calculations of main group elements, such as 13 C, 15 N and 31 P [22][23][24][25][26][27][28]. 13 C and 31 P CSs in nickel and palladium complexes have also been calculated, including taking into account relativistic effects [29][30][31][32][33].…”