Etude par RMN du Proton et du Carbone‐13 de Pyrimidines Substituées. I—Effets de Substituant dans les Dérivés Méthylés et Aminés

Abstract

Substituent effects of methyl and amino groups on the chemical shifts of pyrimidine have been investigated by'H and "C n.m.r. and compared with similar data obtained for benzene and pyridine. Takbg into account pairwise interactions, the chemical shifts calculated by using an additivity relationship are in very good agreement with the experimental results, except for some hindered Pyrimidines. This study enabled us to assign the "C nmr. spectra of some trisubstituted pyrimidines.Les effets de substituant des groupes mCthyle et amino sur les denlacements chimiques de la pyrimidine ont CtC CtudiCs par RMN du proton et du carbone-13 et cornparts h ceux observes pour le benzkne et la pyridine. Compte-tenu des interactions mutuelles des substituants, les dkplacements chimiques calculCs B l'aide d'un schCma d'additivitb sont en trbs bon accord avec les dkplacements chimiques observCs, sauf dans quelques cas concernant des pyrimidines encombrbes. Cette Ctude des effets de substituant a permis l'attribution sans equivoque des spectres du carbone-13 de pyrimidines trisubstitukes.

Proton and carbon-13 nuclear magnetic resonance studies of substituted pyrimidines. 2. Monoprotonation of methyl- and aminopyrimidines

“…The values of ' , a'cH3, and a' calculated for the asymmetric methylpyrimidines (3,5) are in good agreement (different by less than 0.3 ppm) with the corresponding values for the symmetric methylpyrimidines (1,2,4,7,8,9). In order to calculate the populations of the monoprotonated forms in the asymmetric pyrimidines, one therefore uses the average values of the parameters a' and a' determined from the whole series of methylpyrimidines (see Table VIII).…”

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.…”

“…The theoretical basis for the correlations was addressed by several groups. [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.…”

“…[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. 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.…”

“…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.…”