The infrared spectra of caffeine salts

1967 ◽  
Vol 45 (23) ◽  
pp. 2895-2897 ◽  
Author(s):  
Denys Cook ◽  
Zephyr R. Regnier
Keyword(s):  
Nitrogen Atom ◽  
Infrared Spectra ◽  
Imidazole Ring ◽  
Out Of Plane ◽  
Plane Bending ◽  
Bending Modes

The infrared spectra of caffeine and its salts show that protonation occurs at position 9, the free nitrogen atom in the imidazole ring. N+H stretching and in-plane and out-of-plane bending modes have been assigned with the help of the deuterated salts. Protonation causes changes in some ring modes, accompanied by shifts in the carbonyl stretching frequencies to higher values.

The infrared spectra of theobromine salts

1967 ◽  
Vol 45 (23) ◽  
pp. 2899-2902 ◽  
Author(s):  
Denys Cook ◽  
Zephyr R. Regnier
Keyword(s):  
Hydrogen Bond ◽  
Nitrogen Atom ◽  
Infrared Spectra ◽  
Imidazole Ring ◽  
Free Base ◽  
Absorption Bands ◽  
Out Of Plane ◽  
Stretching Vibrations ◽  
Deformation Modes ◽  
Infrared Absorption Bands

From the infrared spectra of theobromine salts it is concluded that the salts are probably arranged in hydrogen-bonded centrosymmetric pairs involving [Formula: see text] interactions. [Formula: see text] anion− hydrogen bonds are formed by protonation of the free nitrogen atom (N9) in the imidazole ring. Infrared absorption bands arising from the former hydrogen bond constantly appear near 3 000 cm−1, whereas those from the latter shift from 2 580 to 3 300 cm−1, depending on the anion. In-plane NH and N+H deformation modes give bands near 1 485 and 1 160 cm−1, respectively. Out-of-plane NH modes have been located, but precise assignments are not possible.The assignments for some other bands which show deuteration shifts are detailed, and the carbonyl stretching vibrations which increase in frequency on protonation of the free base are identified.

Investigation of Spectral Sensitization V. A Study of the Visible and Infrared Spectra of Some Very Pure 2-bis-Benzoxazolyl, 2-bis-Indolinyl, and 2-bis-Quinolyl Cyanine Iodides

1967 ◽  
Vol 21 (2) ◽  
pp. 71-80 ◽  
Author(s):  
A. Leifer ◽  
D. Bonis ◽  
M. Boedner ◽  
P. Dougherty ◽  
A. J. Fusco ◽  
...  
Keyword(s):  
Infrared Spectra ◽  
Absorption Maximum ◽  
Low Frequency ◽  
Cyanine Dyes ◽  
Visible Range ◽  
Bending Vibrations ◽  
Out Of Plane ◽  
Phenyl Rings ◽  
Plane Bending ◽  
Bending Modes

A detailed study of the visible spectra in solution and the infrared spectra in the solid state has been made for the following vinylogous series of cyanine dyes: [2-bis(3-ethylbenzoxazolyl)] cyanine iodides, [2-bis-(1-ethyl-3,3-dimethylindolinyl)] cyanine iodides, and [2-bis-(1-ethylquinolyl)] cyanine iodides. Each dye, to be acceptable for study, had to be chromatographically pure, give a correct microchemical elemental analysis, and be free of electron-spin-resonance (free-radical) signals. The characteristic red shift of the principal absorption maxima was observed for these dyes in the visible range as the number of methine linkages increased. A careful comparison of the visible spectral data of the [2-bis(3-ethylbenzoxazolyl)] cyanine iodides with those of the corresponding [2-bis(3-ethylbenzothiazolyl)] and [2-bis(3-ethylbenzoselenazolyl)] cyanine iodides, [Leifer et al., Appl. Spectry. 20, (1966)] indicates that the electronegativity of the atom S, Se, or O in the heterocyclic rings probably affects the wavelength of the principal absorption maximum. As the electronegativity of the Group VI.A atom increases, the principal absorption maximum shifts slightly toward the blue. Assignments of vibrational modes to separate absorption regions have been made for these vinylogous series of dyes. Each vinylog has a characteristic pattern of resonant-conjugated stretching modes in the region 1600–1400 cm−1. Some of these modes exhibit a low frequency shift as the resonant-conjugated chain increases. Comparison of the benzoxazolyl modes with those of the corresponding benzothiazolyl and benzoselenazolyl modes indicates that they are probably a function of the electronegativity of S, Se, or O in the heterocyclic rings. As the electronegativity of the VI.A atom increases, the resonant-conjugated stretching modes shift to higher frequencies. There are also characteristic bands in the 1600–1400 cm−1 region which are present in all the vinylogs of each series of these dyes. These bands have been assigned to the stretching modes of the fused phenyl rings present in these dyes. It appears that the fused phenyl stretching modes are a function of the groupings C(CH3)2, O, S, Se present in the indolinyl, benzoxazolyl, benzothiazolyl, and benzoselenazolyl heterocyclic rings, respectively. The sulfur and selenium atoms affect these modes the least while the oxygen atom affects these modes the most. Assignments have been made for the aromatic CH out-of-plane bending modes in the region 800–700 cm−1 for these vinylogous series of cyanine dyes. In the spectra of the 2-bis-indolinyl and 2-bis-quinolyl cyanine iodides, there is a band appearing in the region 1000–900 cm−1 which changes systematically with an increase in the number of hydrogens on the bridge. This band has been assigned to the out-of-plane bending vibrations of the hydrogens in a trans configuration on the bridge. No evidence of a cis isomer was observed in the spectra.

Infrared spectra and hydrogen bonding in some methyl α-glycopyranosides

1975 ◽  
Vol 28 (2) ◽  
pp. 335 ◽  
Author(s):  
AJ Michell
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bonding ◽  
Infrared Spectra ◽  
Bending Vibrations ◽  
Ambient Temperatures ◽  
Out Of Plane ◽  
Stretching Vibrations ◽  
Plane Bending

Spectra in the OH stretching and out-of-plane bending regions of four methyl α-glycopyranosides of known crystal structure have been obtained at ambient and sub-ambient temperatures. Partial deuteration has been used to uncouple the stretching vibrations and assist in assignments of the out-of-plane bending vibrations.

Investigation of Spectral Sensitization IV. A Study of Visible and Infrared Spectra of Some Very Pure Bis—Benzothiazolyl and Bis—Benzoselenazolyl Cyanine Iodides

1966 ◽  
Vol 20 (5) ◽  
pp. 289-297 ◽  
Author(s):  
A. Leifer ◽  
D. Bonis ◽  
M. Boedner ◽  
P. Dougherty ◽  
M. Koral ◽  
...  
Keyword(s):  
Infrared Spectra ◽  
Low Frequency ◽  
Bending Vibrations ◽  
Crystal Field Effect ◽  
Spin Resonance ◽  
Visible Spectra ◽  
Out Of Plane ◽  
Phenyl Rings ◽  
Plane Bending ◽  
Cis Isomer

A detailed study of the visible spectra in solution and the infrared spectra in the solid state have been made for the following vinylogous series of dyes: [2-bis(3-ethylbenzothiazolyl)] cyanine iodides and [2-bis(3-ethylbenzoselenazolyl)] cyanine iodides. Each dye, to be acceptable for study, had to be chromatographically pure, give a correct microchemical elemental analysis, and be free of electron-spin resonance (free radical) signals. The characteristic red shift of the principal absorption maxima was observed for these dyes in the visible as the number of methine linkages increased. Assignments of vibrational modes to separate absorption regions have been made for these vinylogous series of dyes. Each vinylog has a characteristic pattern of resonant-conjugated stretching modes in the region 1600–1400 cm−1. These modes exhibit a low-frequency shift as the resonant-conjugated chain length increases. There are bands absorbing in the regions 1594–1572 cm−1 and 1470–1453 cm−1 which are present in all the vinylogs and which have been assigned to the aromatic stretching vibrations of the fused phenyl rings present in all these dyes. There is a band appearing in the region 1000–900 cm−1 which changes systematically with an increase in the number of hydrogens on the bridge and with substitution on the bridge. This band has been assigned to the out-of-plane bending vibrations of the hydrogens in a trans configuration on the bridge. No evidence of a cis isomer was observed in the spectra. There is a band near 760 cm−1 which is split into a doublet and has been assigned to the aromatic CH out-of-plane bending vibrations of the four adjacent hydrogens on the fused phenyl rings. This splitting has been attributed to a crystal field effect which gives rise to in-phase and out-of-phase vibrations of the same groups in two different molecules.

scholarly journals The CH out-of-plane bending modes of PAH molecules in astrophysical environments

2001 ◽  
Vol 370 (3) ◽  
pp. 1030-1043 ◽  
Author(s):  
S. Hony ◽  
C. Van Kerckhoven ◽  
E. Peeters ◽  
A. G. G. M. Tielens ◽  
D. M. Hudgins ◽  
...  
Keyword(s):  
Out Of Plane ◽  
Plane Bending ◽  
Bending Modes
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