FT-IR and FT-Raman spectra of 6-chlorouracil: Molecular structure, tautomerism and solid state simulation. A comparison between 5-chlorouracil and 6-chlorouracil

6-Aminouracil: Geometries and spectra in the isolated state and in the solid state simulation. A comparison with 5-aminouracil

“…This mode is scaled at 430 (IR) and 404 (Raman) cm À1 , in the tetramer form in agreement with the experimental strong IR band at 443 cm À1 and with the Raman band with weak intensity observed at 421 cm À1 . This assignment finds further support from that reported experimentally in 5-aminoU at 418 cm À1 (IR) and 418.9 cm À1 (Raman) [62], in 5-chlorouracil at 446 cm À1 (IR) and 457 cm À1 (R) [66], in 6-chlorouracil at 451 cm À1 (IR) and 443 cm À1 (R) [12], and in 5-fluorouracil at 419 cm À1 (IR) and 413 cm À1 (R) [65]. The experimental bands reported at 430 [25], 416 [26] and 450, 430 [27] cm À1 were reassigned to this inplane bending mode, instead of its assignment by these authors and 734 (Raman) cm À1 , and it was related to the experimental band at 764 cm À1 in IR and 768 cm À1 in Raman.…”

“…This feature together with the clear observation of n(C]O) modes as strong bands in the experimental spectra shows that in the solid state 6-aminoU is only in the keto tautomer. The strong coupling observed in the uracil spectrum continues highly constant for its 6-aminoU, and as well for other derivatives [12,62]. Table 5.…”

“…Moreover, these authors have assigned this mode to a band that they have observed at 1865 cm À1 , but that we have not detected, neither even something closely, in the present study. The wavenumber at 1865 cm À1 is far from those found experimentally by IR in related molecules, as example at 1757.5 cm À1 (uracil) [51], 1745 cm À1 (5-aminoU) [64], 1734 cm À1 (6-chlorouracil) [12] and 1720 cm À1 (5-fluorouracil) [65]. Consequently we have reassigned these experimental bands in 6-aminoU.…”

“…In 5-aminoU it was assigned to the band at 1675 cm À1 [62], in 6-chlorouracil at 1676 cm À1 [12] and in 5-fluorouracil at 1670 cm À1 [65].…”

“…[25e27]. In 6-chlorouracil [12] the very weak IR band detected at 3439 cm À1 was assigned to n(N1eH), while the very strong one at 3094 cm À1 was related to n(N3eH).…”