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Density Functional Theory/GIAO Studies of the 13C, 15N, and 1H NMR Chemical Shifts in Aminopyrimidines and Aminobenzenes: Relationships to Electron Densities and Amine Group Orientations

“…The 1 H, 13 C, and 15 N NMR chemical shifts of nitrogen heterocyclic compounds have been the subject of a number of experimental and theoretical studies. − There have also been a number of NMR studies of chemical shifts in aminobenzenes , and aminopyrimidines. − An important aspect of magnetic shielding in amine-substituted aromatic compounds, which appears not to have been addressed in previous NMR studies, is the dependence of NMR chemical shifts on amine group orientations. Experimental and theoretical studies of amine substituted aromatic compounds show that the amine group hydrogens are out of the plane by an amount which depends on a balance between π-electron delocalization across the C−N bond and the tendency of the amine group to form strongly directed sp 3 -hybridized orbitals. − There are relatively few structural studies among these compounds because of spectral complexity arising from multiple, large-amplitude vibrations associated with low NH 2 torsion and inversion barriers.…”

“…[3][4][5][6] The 1 H, 13 C, and 15 N NMR chemical shifts of nitrogen heterocyclic compounds have been the subject of a number of experimental and theoretical studies. [7][8][9] There have also been a number of NMR studies of chemical shifts in aminobenzenes 10,11 and aminopyrimidines. [12][13][14][15][16][17] An important aspect of magnetic shielding in amine-substituted aromatic compounds, † Pharmacia and Upjohn Inc. X Abstract published in AdVance ACS Abstracts, September 1, 1997. which appears not to have been addressed in previous NMR studies, is the dependence of NMR chemical shifts on amine group orientations.…”

“…Presented here are experimental and calculated 13 C, 15 N, and 1 H isotropic NMR chemical shifts for benzene (1), pyridine (2), aniline (3), pyrimidine (4), 2-aminopyridine (5), 1,3-diaminobenzene (6), 1,3,5-triaminobenzene (7), 2-aminopyrimidine (8), 4-aminopyrimidine ( 9), 4,6-diaminopyrimidine (10), 2,4,6triaminopyrimidine (11), and 2,4-diamino-6-(1-piperidinyl)pyrimidine (desoxyminoxidil) (12). The computational methods for molecular structures and magnetic shielding are presented in the next section.…”

Additional insights from very‐high‐resolution 13C NMR spectra of long‐chain n‐alkanes

“…However, far more common have been reports of just four or five 13 C signals resolved in the spectra of long‐chain n ‐alkanes: four 13 C signals for n ‐nonadecane ( n ‐C 19 H 40 , 19 ) in CCl 4 ; four 13 C signals for 20 neat or in CCl 4 ; five 13 C signals for 11 neat, in CDCl 3 , or in 4.1/0.8/5.1 v/v/v 11 /indan/CCl 4 ; five 13 C signals for 12 neat, in CHCl 2 CHCl 2 , in C 6 D 6 , or in 4.1/0.8/5.1 v/v/v 12 /indan/CCl 4 ; five 13 C signals for 13 neat; five 13 C signals for n ‐tetradecane ( n ‐C 14 H 30 , 14 ) neat or in CDCl 3 ; five 13 C signals for n ‐pentadecane ( n ‐C 15 H 32 , 15 ) neat 13 or in CDCl 3 ; five 13 C signals for 16 neat, in CDCl 3 , or in 4.1/0.8/5.1 v/v/v 16 /indan/CCl 4 ; five 13 C signals for 17 in CDCl 3 ; five 13 C signals for 18 neat, in CCl 4 , in 4.1/0.8/5.1 v/v/v 18 /indan/CCl 4 , or in 1‐chloronaphthalene; five 13 C signals for 19 in CDCl 3 ; five 13 C signals for 20 neat, in CDCl 3 , in CCl 4 , or in 1‐chloronaphthalene; and five 13 C signals for n ‐docosane ( n ‐C 22 H 46 , 22 ) in CDCl 3 . Thus, one could reasonably infer from the 1986 report of at least partial resolution of the ten different 13 C signals of 20 in 10/90 v/v C 6 D 6 /1‐chloronaphthalene at just 9.4 T (100.56 MHz 13 C) that this mixed solvent, rather than either of the individual solvent components, and a field strength higher than those used to study 20 in 1‐chloronaphthalene (20.09 MHz 13 C) or 18 in C 6 D 6 (67.8 MHz 13 C) are required to achieve such resolution.…”