¹H, ¹³C, ¹⁵N NMR and Theoretical Study of Protonated Carbamic Acids and Related Compounds¹

Abstract

Mono-O-protonated carbamic acid, mono-O-protonated N-methyl carbamate, and mono-O-protonated methyl carbamate and di-O-protonated N,N-bis(carboxyl)-1,2-diaminoethane were prepared in FSO 3 H/SO 2 ClF and FSO 3 H:SbF 5 /SO 2 ClF at -78 °C and were characterized by 1 H, 13 C, and 15 N NMR spectroscopy. Persistent diprotonated carbamic acid, diprotonated N-methyl carbamate, and diprotonated methyl carbamate were not observed under these conditions. The structures, energies, and 13 C and 15 N NMR chemical shifts of mono-, and diprotonated carbamic acids as well as other protonated species were also calculated by ab initio/IGLO/GIAO-MP2 method and compared with the experimental results.

A theoretical study on NH bond dissociation enthalpies of oxo, thio and seleno carbamates and their N-protonated and N-deprotonated species

“…Following Scott and Radom rules [39] all scaled torsional modes below 260 cm À1 are replaced by classical rotational limit 1 2 RT. Since the H-atom has no rotational and vibrational contribution the expression for enthalpy for the H-atom becomes…”

“…The NAH BDEs for neutral carbamates, N-protonated and Ndeprotonated carbamates (1)(2)(3)(4)(5)(6)(7)(8)(9) are reported at ROB3LYP/6-311++G(d,p)//B3LYP/6-31+G * theoretical level in Table 2. As can be seen from the Table 2, the NAH BDEs of carbamates with X = O and Y = O, S, Se are higher than the NAH BDE of NH 3 at RO-B3LYP/6-311++G(d,p)//B3LYP/6-31+G * theoretical level.…”

“…Carbamates are biologically important as they are present as substructures in amino acids and many other biologically important molecules [1]. These are recognized for their usefulness in various industries [2][3][4] as agrochemicals [3][4][5] (herbicides, fungicides and pesticides), in pharmaceuticals industry [3,4,6] as drug intermediates, and in the polymer industry [3,4] in the synthesis of polyurethane and also in peptide syntheses [7].…”

Carbocations in Superacid Systems

“…685,686 There is, however, a notable exception. Dication 382a was calculated 694 to have a longer CÀN bond compared to protonated carbamic acid (1.478 versus 1.312 Å). 690 Protonated urea (uronium ion) is a resonance-stabilized cation.…”

“…N,N-bis(carboxyl)-1,2-diaminoethane 383 was also generated by protolytic ionization694 [Eq. (3.108)].…”