Infrared interpretation

Saperstein, D.D. "A Scheme For Optimized Infrared Interpretations , paper // 216, 1985. Pittsburgh Conference Exposition on Analytical Chemistry and Applied Spectroscopy, Feb. 25-March 1, 1985. 

The current protot3rpe system includes three Expert modules, the IR Expert, the STIRS Expert, and the Human. All modules are written in Lisp. The IR Expert is a rule-based infrared interpreter which we have developed. The STIRS Expert is an interface to the STIRS program, a pattern-matching mass spectrum interpreter developed by McLafferty and coworkers at Cornell University, which is written in Fortran. () ) The interface translates the output of STIRS into a form palatable to our program, and handles the message-passing protocol required by the Controller. The Human module controls communication with the user. It allows user-supplied elemental or substructure information to influence the course of the analysis. The power of... 

The authors express their thanks to D. Young of these laboratories for his helpful infrared interpretations and to D. Campbell of the Research Triangle Institute for his contribution to the ESR studies. 

The microunit operation by B. Bicknell, gas chromatography analysis by J. stockinger, infrared interpretations by J. Ehlers and discussions with F. Krambeck on the equilibrium data are all acknowledged with thanks. 

A comparison of the infrared spectra of 4-pyridone and l-methyl-4-pyridone in the solid states shows that the bands at 1635 cm" are not much different but that the 1534 cm" band of 4-pyridone is shifted to near 1550 cm" and sharpens in l-methyl-4-pyridone, consistent with the expected shift from a hydrogen bonded to a nonhydrogen bonded carbonyl. However, a comparison of the spectra of 3,5-dihalo-, 3,5-dihalo-l-methyl-, 2,3,5,6-d, l-d-, and I-methyl-4-pyridones has led to the conclusion that both C=0 and C=C stretchings are extensively mixed to give composite vibrations at both frequencies. These difficulties have not negated the earlier structure assignments of 4-pyridones that have been based on infrared interpretations. 

M. E. Elyashberg, Infrared spectra interpretation by the characteristic frequency approach, in The Encyclopedia of Computational Chemistry,... 

Interpretation of spectra. The infrared spectrum of m-hydroxybenzoic acid (solid ground in Nujol) is shown in Fig. A, 7, 1. The more important bands may be interpreted as follows. 

Alkylidenehydrazinothiazoles (297) can be prepared either from 2-hydrazinothiazoles (549) or by direct heterocyclization (527). Their characteristic infrared bands have been reported (550). The main mass spectrometric peaks of (4-coumarinyl-2-thiazolyl)hydrazone (302) (Scheme 179) (134, 551) are situated at mle = 361. 244, 243, 118, 216, 202, 174, 117 the proposed interpretation of the fragmentation pattern should, however, be reconsidered. Scheme l80 summarizes some representative reactions of this class of compounds. 

Infrared and Raman spectra of A-4-thiazoline-2-thione and of isotopi-cally labeled derivatives (56. 59) were interpretated completely. (Table VII-41. 

Auto-association of A-4-thiazoline-2-thione and 4-alkyl derivatives has been deduced from infrared spectra of diluted solutions in carbon tetrachloride (58. 77). Results are interpretated (77) in terms of an equilibrium between monomer and cyclic dimer. The association constants are strongly dependent on the electronic and steric effects of the alkyl substituents in the 4- and 5-positions, respectively. This behavior is well shown if one compares the results for the unsubstituted compound (K - 1200 M" ,). 4-methyl-A-4-thiazoline-2-thione K = 2200 M ). and 5-methyl-4-r-butyl-A-4-thiazoline-2-thione K=120 M ) (58). 

Until 1962 the infrared and Raman spectra of thiazole in the liquid state were described by some authors (173, pp. 194-200) with only fragmentary assignments. At that date Chouteau et al. (201) published the first tentative interpretation of the whole infrared spectrum between 4000 and 650 cm for thiazole and some alkyl and haloderivatlves. They proposed a complete assignment of the normal modes of vibration of the molecule. 

The infrared and Raman spectra of many alkyl and arylthiazoles have been recorded. Band assignment and more fundamental work has been undertaken on a small number of derivatives. Several papers have been dedicated to the interpretation of infrared spectra (128-134, 860), but they are not always in agreement with each other. However, the work of Chouteau (99, 135) is noteworthy. The infrared spectrum of thiazole consists of 18 normal vibrations as well as harmonic and combination bands. 

A solubihty parameter of 24.5-24.7 MPa / [12.0-12.1 (cal/cm ) ] has been calculated for PVF using room temperature swelling data (69). The polymer lost solvent to evaporation more rapidly than free solvent alone when exposed to air. This was ascribed to reestabUshment of favorable dipole—dipole interactions within the polymer. Infrared spectral shifts for poly(methyl methacrylate) in PVF have been interpreted as evidence of favorable acid—base interactions involving the H from CHF units (70). This is consistent with the greater absorption of pyridine than methyl acetate despite a closer solubihty parameter match with methyl acetate. 

Experiments designed to clarify the situation were carried out by Wittig and Mayer (40). It was shown that changing the molar ratio of amine (diethylamine, di- -butylamine, or diisobutylamine) to -butyraldehyde from 1 1 to 2 1 did not affect the yield of enamine (53- 64%, based on the aldehyde). Contrariwise, changing the ratio of amine (morpholine, piperidine, or pyrrolidine) to n-butyraldehyde from 1 1 to 2 1 boosted the yields from 52-57 % to 80-85 %. The authors interpret these data as indicating that the cyclic amines form aminals with n-butyraldehyde, while the open-chain do not. Infrared evidence is stated as having shown that the aminal originates not from attack of excess amine on the enamine, which is stable under the conditions of the reaction, but from the N-hemiacetal (17). 

The interpretation of these remarkable properties has excited considerable interest whilst there is still some uncertainty as to detail, it is now generally agreed that in dilute solution the alkali metals ionize to give a cation M+ and a quasi-free electron which is distributed over a cavity in the solvent of radius 300-340 pm formed by displacement of 2-3 NH3 molecules. This species has a broad absorption band extending into the infrared with a maximum at 1500nm and it is the short wavelength tail of this band which gives rise to the deep-blue colour of the solutions. The cavity model also interprets the fact that dissolution occurs with considerable expansion of volume so that the solutions have densities that are appreciably lower than that of liquid ammonia itself. The variation of properties with concentration can best be explained in terms of three equilibria between five solute species M, M2, M+, M and e ... 

Values for Ihe gas phase are sirtrilar bin there is a notice-able conlfaction in the cubic crystalline form (in parenlhe-ses). N - N 175 pm (164 pm). N - O 118 pm (117 pm), angle O-N-0 133.7 (126°). In addition, infrared studies on N2O4 isolated in a low-temperature matrix at liquid nitrogen temperature ( - 1%°C) have been interpreted in terms of a twisted... 

In tetrahedral fields the splitting of the free ion ground term is the reverse of that in octahedral fields so that, for d ions in tetrahedral fields A2g(F) lies lowest but three spin-allowed bands are still anticipated.In fact, the observed spectra usually consist of a broad, intense band in the visible region (responsible for the colour and often about 10 times as intense as in octahedral compounds) with a weaker one in the infrared. The only satisfactory interpretation is to assign these, respectively, as, wj = 7 i (P)-i A2(F) and ut = i(F)- A2(F) in which case U = ) should be... 

Vibrational frequencies Calculated vibrational frequencies are larger than measured values, typically by about 12%. Systematic scaling of calculated frequencies (by 0.88) leads to values which are generally suitable for assignment and interpretation of experimental infrared/Raman spectra. 

In 1951, Witkop et al. interpreted the infrared spectra of quinol-2-and -4-ones to favor the oxo formulation. Since then, many investigators, especially Mason, have reported that potential a- and y-hydroxy compounds show infrared absorption bands in the vN—H (3500-3360 cm ) and vC—O (1780-1550 cm ) regions of the spectrum and, hence, exist predominantly in the oxo form references to this work appear in Table I. A study of the bands which occur in the NH-stretching region of the infrared spectra of a series of substituted pyrid-2-ones and quinol-2-ones also supported an oxo formulation for these compounds. Detailed band assignments have been published for pyrid-2- and -4-one. Mason has reported that solutions of j8-hydroxy compounds in chloroform or carbon tetrachloride show... 

The infrared spectra of 2- and 4-hydroxy quinoline 1-oxide have been interpreted to favor forms 55 and 56,. respectively. Lehm-stedt has discussed the tautomerism of 10-hydroxyacridone (57 58) but reached no definite conclusions. Igeta investigated the... 

Pyrimidinones have been extensively investigated because of their importance in the chemistry of natural products. Initially, the infrared spectra of the hydroxypyrimidines were interpreted to favor their existence in the hydroxy form ° however, in 1952 Short and Thomp-goniso reinvestigated these compounds and concluded that pyrimidin-2- and -4-one probably exist in the oxo form. Solid-state infrared spectra were used in this early work which probably accounts for the difficulties encountered in their interpretation. Brown and his asso-... 

The structure of malonyl-a-aminopyridine (cf. 121) has been discussed by Snyder and Robinson/ who interpreted the infrared and ultraviolet spectra and the fact that it could be converted into a monochloro derivative (122, R = Cl) to indicate that the intra-molecularly hydrogen-bonded hydroxy form 122 (R = OH) was predominant. However, comparison of the basicities of the methoxy compound 122 (R = OMe), the mesomeric betaine 123 (R = Me), and the parent compound indicates that in aqueous solution the last exists mainly in the zwitterion form 123 (R = H), ... 

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