Vibrational spectra and normal coordinate analyses of vinyl cyanamide in the planar conformation

Copper-Catalyzed Alkenylation of Cyanamides

An efficient procedure for the copper-catalyzed cross-coupling between a broad range of cyanamides and iodoalkenes is reported. Upon reaction with catalytic amounts of copper(I) iodide and 2,2'-bisimidazole in the presence of cesium carbonate in DMF at 80 °C, a fast, regioselective, and stereoretentive cross-coupling occurs. This reaction, which was found to have a broad substrate scope, provides the first general entry to N-alkenylcyanamides, building blocks that hold great synthetic potential.

ROTATIONAL BARRIERS AND VIBRATIONAL SPECTRA OF PHENYL KETENE, AZIDE, AND ISOCYANATE

Our interest in conjugation effects in substituted phenyl compounds has turned our attention to the highly reactive compounds phenyl ketene, azide, and isocyanate, which due to their reactivity are of utmost importance in organic synthesis. We performed local density functional theory (DFT) calculations using a 6-311G** basis set to calculate the structures and potential functions of the internal rotation. Further for the minimum structures we computed the vibrational infrared and Raman spectra of the three molecules. In order to confirm that DFT works rather well in these systems we performed the geometry optimizations also using ab initio Moeller–Plesset perturbation theory of second order (MP2) in the same basis set. As expected there exist just two minimum structures for each of the molecules which both correspond to planar structures and are identical due to the symmetry of the phenyl ring. The transitions states (TS) of the internal rotations are the perpendicular ones. We expect conjugation to play no major role in these molecules since extensive conjugation effects would imply a large reduction of the aromatic character of the phenyl ring which in turn would greatly destabilize the systems. However, although the rotational barriers appear to be rather small in these systems conjugation must play at least some role in stabilizing the planar ground state. As detailed later, the relative heights of the rotational barriers can all be explained naturally. Experimental vibrational spectra could be obtained only for phenyl isocyanate and azide, but not for the ketene because of the high reactivity of this molecule. Since in the former cases the calculated spectra agree fairly well with the measured ones, we present those of the other molecule as theoretical prediction, which could be useful to detect spectroscopically in a reaction mixture residual reactant. On the basis of potential energy distribution (PED) calculations we present a complete assignment of the vibrational lines to symmetry coordinates, where, for example, ring breathing must show up with rather large intensities in the Raman spectra of the molecules.

Rotational barriers in monomeric CH2=CX-COOH and CH2=CX-CONH2 (X is H or CH3) and vibrational analysis of methacrylic acid and methacrylamide

The internal rotations in acrylic and methacrylic acids CH2=CX-COOH and their amides CH2=CX-CONH2 (X is H or CH3) were investigated by DFT-B3LYP calculations with 6-311+G** basis set. The potential energy curves were consistent with two minima that correspond to planar cis and trans conformation in the case of the acids (or cis and near-trans forms in the case of the amides). Acrylic acid and acrylamide were predicted to have the cis form as the low and predominant conformation of the molecules. In the case of the methacrylic acid and methacrylamide, the conformational relative stability was predicted to reverse as going from the acrylic to the metha compounds. The trans conformer in methacrylic acid or the near-trans in methacrylamide were predicted to be thermodynamically low energy structures of the molecules. The CCCO rotational barrier was calculated to vary from 4 to 6kcal/mol in the four molecules. The OCOH and OCNH torsional barriers were calculated to be about 13 and 22kcal/mol in the acids and the amides, respectively. The vibrational frequencies of methacrylic acid and methacrylamide were computed at the DFT-B3LYP/6-311+G** level and reliable vibrational assignments were made on the basis of normal coordinate analyses and comparison with experimental data of both molecules in their low energy conformations.