PROTONATED Γ-Pyrones

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Salts of a~ltipyri~le (2,3-di1nethyl-l-p11enyl-5-pyrazolone) with halogen acids have been prepared and their infrared spectra froin 4000 to 650 cm-I recorded. Stoichiometrically they are normal 1 : l salts. Identification of bands due to vibrations of the protonating hydrogen atom has been aided by replacement with deuterium atoms. I t is concluded that protonation occurs a t the carbonyl group from the presence of a doublet (due to correlation field splitting) a t 1320 and 1220 cm-I, attributed to the in-plane hydrogen-bending mode. The OH stretching vibration gives rise to bands between 2278 and 2720 cm-1 in the different salts. Out-of-plane hydrogen-bending mode absorptions are observed between 840 and 770 cm-'.More complex acids (HAsFs etc.) give the anomalous 2 base: 1 acid salts, characterized by strong absorption below 1400 cm-', which probably contain strong, possibly symmetrical, hydrogen bonds. IXTRODUCTIONInfrared spectroscopic methods have been used recently to ascertain the protonation site in colnpounds containing carbonyl groups. 4-Pyrones (1) and 4-pyridones (2) were shown to protonate a t the carbonyl group oxygen atom, and not a t the heterocylic atom. The bending mode of the 0+-H group gives rise to absorption bands near 1260 cm-I _ (mean value of two components ascribed to correlation field splitting). Thus, while the OH stretching vibration absorption, which can be observed between about 2400 and 3400 cm-I depending on the anion, is diagnostically of little use, except to indicate that protonation has taken place, the bending mode, 80H, shows increasing dependable utility as an indication of the site of protonation.A recent study of the infrared spectra of N,N-dicyclohexylaceta~nide salts (3) showed the bending mode to absorb near 1287 cm-l, a rather higher value than in y-pyrones ( I ) and y-pyridones (2), and with a smaller shift on deuteration. The mesomeric system in amides which is responsible for much vibrational coupling (4) may also give rise to the same effects in the salts. I t is of interest therefore to investigate further systems containing the -NRCOgrouping. The salts of antipyrine (2,3-dimethyl-1-phenyl-5-pyrazolone) are described a t this time. RESGLTSThe infrared spectrum of the HCl salt of antipyrine is shown in Fig. 1, the broken line being the DCl salt. The bands in the spectra are collected in Table I , and the bands associated with vibrations of the protonating hydrogen atom are summarized in Table 11. DISCUSSION The broad strong band in the spectra near 2300 cm-I is associated with the OH stretching vibration of the protonated carbonyl group as in I. As Y -gets larger and the effect of its force field diminishes V O H gets larger, indicative of a decreasing interaction in the hydrogen bond 0+-H. . -Y-. In the deuterium substituted salts (I, H = D) the isotopic 'Contribution No. 107.

“…Thus the 1496 cm-I band is close in frequency t o other bands due to a protonated carbonjrl stretching vibration (1,2). These are listed under the heading VC=O+H in Table 111.…”

Section: Discussionmentioning

confidence: 71%

Protonated Carbonyl Groups: Iii. Antipyrine Salts

Cook¹

1963

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“…A further point became clear in that 4-pyrones protonate at the carbonyl oxygen atom, and not a t the heterocyclic oxygen atom (2).…”

Section: Introductionmentioning

confidence: 99%

Infrared Spectra of Complexes of 4-Pyridones

Cook¹

1963

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The infrared spectra of many complexes of Lewis acids with some 4-pyridones have been recorded. Large shifts t o lower frequencies of about 100 cm-I have been observed in a band near 1560 cm-1 as the Le~vis acid strength increased. Much srnaller shifts of about 5 to 10 cm-1 in a band near 1640 cm-I were noted. The former band has therefore been designated a s the carbonyl frequency, and the latter as a ring mode involving C C stretching.The donor site of 4-pyridones is therefore the carbonyl group, and not the nitrogen atom. Protonated 4-pyridones have similar spectra, and are consistent with 0 -, not N-protonation.

“…The first article in this series gave an interpretation of the infrared spectra of protonated 7-pyrones (1). The simplicity of the spectra, in particular the absence of deuteration shifts in bands other than those due to the OH group, made the assignments relatively straightforward.…”

Section: Introductionmentioning

confidence: 99%

PROTONATED CARBONYL GROUPS: V. Α-Pyridone SALTS

Cook¹

1965

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Salts of 1-methyl-2-pyridone and 1-methyl-2-quinolone with strong acids have been prepared and their infrared spectra recorded between 4 000 and 650 cm−1. Protonation of the carbonyl group occurs giving rise to OH stretching, in-plane and out-of-plane bending vibrations which absorb in characteristic regions of the spectrum, namely 1 900 – 3 300 cm−1 (depending on the anion), ~ 1 250 cm−1, and ~ 800 cm−1 respectively, with appropriate shifts on deuteration. Other tentative assignments are made.