Non-planarity of the aniline molecule

The p.m.r. spectra of 2-chloroaniline and 2-chloroaniline-15N in benzene and toluene solutions are analyzed at 60 and 100 MHz under conditions where the amino protons are exchanging intermolecularly and also where they are not exchanging. The spectrum of 2-chloroaniline-H15ND in the absence of amino proton exchange is observed between -48 and 80 "C. In all situations fast rotation about the C-N bond evidently occurs. Long-range couplings of the amino protons to all ring protons are observed and their signs are determined. The nonplanarity of the amino group is discussed in terms of the longrange couplings, of the one-bond 15N-H couplings, and of the two-bond H-H couplings in the amino group. The signs and magnitudes of the coupling constants between the ring protons and 15N are also determined.Les spectres de r.m.p. des 2-chloroaniline et 2-chloroaniline 15N dans des solutions de benzene et toluene sont analysts a 60 et 100 MHz dans des conditions telles que l'echange intermolCculaire des protons de l'azote ait lieu, ainsi qu'en absence d'echange. Le spectre de la 2-chloroaniline-HL5ND en l'absence d'tchange est observe entre -48 et 80 "C. Dans tous les cas, la rotation rapide autour de la liaison G-N est mise en evidence. Les couplages a longue distance entre les protons de I'azote et tous les protons du cycle sont determines avec leurs signes. La non-planearite du groupement amine est discutee en termes de couplages a longue distance, de couplage I5N-N et de couplages H-H a travers deux liaisons dans le groupement amine. Le signe et la valeur des constantes de couplages entre les protons du cycle et le noyau 15N sont aussi determines.

“…The estimated degree of nonplanarity is in broad agreement with the microwave data for aniline itself in the gas phase (19), but there is no doubt that the estimate is not very reliable.…”

Section: (2) Nonplanarity Of the Amino Group (A) Long-range Proton-prsupporting

confidence: 74%

Proton Magnetic Resonance Spectrum of 2-Chloroaniline-¹⁵N. Long-range Coupling Constants to Amino Protons from all Ring Protons

Wasylishen¹,

Schaefer²

1971

“…The major isomer, for which the aromatic resonances are easily discerned, is reported in Table I1 (entries 19 and 20). The minor isomer, representing 20% of the molecules in solution, showed methyl proton resonances which closely resembled those of its N-methyl analogue (with the exception of the N-methyl protons, of course) thus fixing its configuration as a trans one (9). The nlajor isomer, therefore, possesses the cis configuration (10) in which the acetyl methyl protons are little affected by the (now distant) benzene ring.…”

Section: B) N-metlzylproton Resotzancesmentioning

confidence: 87%

“…The sensitivity of the acetyl methyl protons to the bulk of the aromatic moiety requires that the N-methylacetanilides exist in a trans configuration about the CO-N bond (9) in order that the methyl group and the aromatic ring be proximate. The choice of type (9) over (10) is in accord with other findings for N-methylacetanilides (4a, 19, 63a,b).…”

Section: B) N-metlzylproton Resotzancesmentioning

confidence: 99%

Proton magnetic resonance spectra of some aromatic amines and derived amides

Brown¹,

Radom²,

Sternhell³

et al. 1968

The chemical shifts of ring protons in substituted anilines, N-methylanilines, some heterocyclic amines, and their derived acetamides and 4'-bromobenzamides are reported. The magnitude of the downfield shift accompanying acylation is related to the preferred configuration of the amide.Canadian Journal of Chemistry, 46, 2577Chemistry, 46, (1968 IntroductionIn connection with another project (1) we have commented on the relation between the downfield shifts of ring protons accompanying acetylation of anilines and the substitution pattern in the aromatic ring. The present work represents a systematic extension of these observations and rationalization of the principal effects observed.

“…Another calculation on aniline assumed complete planarity of the molecule with C-N and N-H bond lengths equal to those given (26) for the nonplanar molecule. Standard geometries were used in a planar (apart from the methyl protons) model of 2-aminoacetophenone.…”

mentioning

confidence: 99%

“…For aniline the geometry of the amino group was taken from the microwave results of Lister and Tyler (26), which give the angle 0 between the extension of the C-N bond and the bisector of the HNH angle as 37.7".…”

mentioning

confidence: 99%

The Geometrical Dependence of Experimental and Theoretical Nuclear Spin–Spin Coupling Constants in the ¹⁵NH₂ Fragment

Wasylishen¹,

Schaefer²

1973

Approximate molecular orbital theory at the INDO level of approximation has been used to examine 1J(15N,H) and 2(HNH) in ammonia as a function of the HNH angle. The couplings are very sensitive to the value of the HNH angle in the range from 110 to 120°. The computed trends are compared with those observed in other compounds containing the 15NH2 fragment. The signs and magnitudes of 1J(15N,H) and 2J(HNH) have been measured for 2-aminoacetophenone at temperatures where the amino protons are nonequivalent. The observed and calculated results suggest that the amino group lies in the plane of the benzene ring. In aniline the magnitude of 2J(HNH) lies between 1 and 2 Hz and on the basis of the trends in the calculated and experimental values the sign can be confidently taken as negative.