¹⁵N NMR, ¹H NOE difference spectroscopy and conformation of N‐(o‐aminophenyl)‐N′‐alkylureas

Abstract

The "N NMR spectra of five N-(o-aminopheny1)-N substituted ureas and their hydrochloride salts were recorded in DMSO. N-1 was more shielded in these ureas than in N-phenyl-N-methylurea. The shifts of N-3 varied with the substituents. Proton exchanges a t N-3 were observed when the spectra of the hydrochloride salts were recorded. The preferential trans-trans orientation of the protons with respect to the carbonyl in the ureido group was confirmed by NOE difference spectroscopy. In the solid, the conformation of N(o-aminopheny1)-N-methylurea, which was determined by x-ray diíüaction, was found to be similar to the suggested conformation in solution; the "N shifts of this compound in the solid state were determined by "N cross-polarization magic angle spinning NMR. KEY WORDS 15N NMR 'H N O E difference spectroscopy l-(o-Aminophenyl)-3-alkylureas X-ray structureReceived

Structure of N-(2-aminophenyl)-N'-methylurea

“…The geometry of the title compound in the solid is similar to that of one of its major conformations in solution, as confirmed by NMR spectroscopy results (Jean-Claude & Just, 1992).…”

Structural Similarities and Differences between N-Phenylureas and N-Phenylthioureas

“…42(1) C( 3) 14597( 8) 7568 (5) -1844 (5) 53(2) C( 4) 14102 (7) 8381 (5) -2673(4) 56(2) C( 5) 12392 (7) 8598 (5) -2888( 4) 50(1) C( 6) 11196 (6) 8015…”

“…The interactions within the urea fragment may be described using three resonance structures (Figure 5). Asa result of the conjugation of the lone electron pairs of N atoms with the -electrons of the C=0 bond, an equilization of CN bonds may be expected and also partial charges at the C (7), N(l), N(2), and 0(1) atoms should appear. The planarity of the urea fragmentis very helpful when delocalized molecular orbitals are considered.…”

Oxidation of thiourea and substituted thioureas: a review

“…In N-substituted thioureas, the substituents can adopt four different conformations with respect to the central C9S bond. The preferred conformations have been investigated using 1 H, 13 C, and 15 N NMR spectroscopy in solution (22)(23)(24) as well as in the solid state (25). The stability of different conformers has been predicted by using molecular mechanics (22).…”