I.N. Juchnovski

IR spectra and structure of benzylidenemalononitrile and its cyanide, methoxide and heptylamine adducts: experimental and ab initio studies

Abstract The potassium cyanide, alkali-metal methoxide and heptylamine adducts of benzylidenemalononitrile were prepared as dimethyl sulphoxide (DMSO) and DMSO- d 6 solutions; their structures were studied by IR spectroscopy and ab initio force field calculations. The cyanide and methoxide adducts have a carbanionic structure, whereas heptylamine forms a zwitterion. The IR spectra of the adducts studied are characterized by very intense, low-frequency ν CN bands with a strong ν CN s – ν CN as splitting. The changes in the structure and force field of benzylidenemalononitrile accompanying its conversion into the adducts studied are essential and are spread over the whole molecule. The anionic charge is localized mainly within the dicyanomethide groups of the adducts.

Infrared spectra and structure of carbanions : V. Assignment of the nitrile group infrared bands of the phenyl acetonitrile and acetonitrile lithium derivatives

Abstract The structure of the lithium derivatives of phenyl acetonitrile and acetonitrile is discussed in terms of their IR spectra. It has been found from new and already-published data that the IR spectra [ν(CN) region] of the lithium, sodium, potassium and chlormagnesyl derivatives of phenyl acetonitrile in various solvents, and in the solid state, are similar. They are characterized by very strong ν(CN) bands in the 2068–2102 cm −1 region, and correspond to the mesomeric phenyl acetonitrile carbanion. The ν(CN) bands, found in the 2050–2071 cm −1 region, suggest the structure for lithium acetonitrile, both in solution and in solid state. The influence of the counter ion and the solvent is discussed in terms of the concept of ion-pairs. Some published data are reconsidered; it is shown that up to now, no reliable data on the presence of tautomeric forms of lithium acetonitrile either in solution or in solid state exist. Some odd bands in the spectra of samples of alkali-metal derivatives of phenyl acetonitrile and acetonitrile are assigned to the dimers of the nitriles mentioned above, and the metal derivatives of these dimers.

Infrared spectra and structure of phenylacetonitrile and of its carbanion: an ab initio force field treatment

Abstract The structures of phenylacetonitrile and of its carbanion have been studied on the basis of IR spectroscopic data (including literature results) and of ab initio force field calculations. The assignment (D. Croisat et al., J. Org. Chem., 157 (1992) 6435) of the IR bands of phenylacetonitrile, its d 5 analogue, and their carbanions has been confirmed. An excellent linear correlation ( R = 0.999) has been found between the theoretical and experimental IR frequencies of the species studied. The calculations predict well the strong increase in intensity (five to 42 fold) of the v CN , v S8 and v I9 bands which accompanies the conversion of the phenylacetonitrile molecule to its carbanion. The structures of both sodium and potassium derivatives of phenylacetonitrile in dimethyl sulfoxide are close to that of the kinetically free phenylacetonitrile carbanion. The carbanionic center is practically planar; the cyano group carries a considerable negative charge, but its influence on the carbanionic center is mainly inductive. The carbanionic charge is delocalized over the phenyl ring (0.42 e − ), methide (0.30 e − ), and cyano (0.28 e − ) groups.

Infrared spectra and structure of alkane- and cycloalkanecarbonitriles and of their carbanions: An ab initio force field treatment

Abstract The structure of alkane- and cycloalkanecarbonitriles (seven compounds) and of their carbanions has been studied by both infrared spectrometry and ab initio force field calculations. The carbanions (counter ions Li + , Na + and K + ) have been found to exist mainly as ionic aggregates in hexamethylphosphoric triamide solutions. The calculations describe well the marked decrease, by 124–214 cm −1 , in the nitrile band frequencies and also the strong increase, by 1–2 orders, in the nitrile band integrated intensities which accompany the conversion of the parent neutral molecules into carbanions. Cyclopropanecarbonitrile is remarkable as having the highest nitrile band intensity among all the neutral molecules and the lowest one among all the carbanions studied. This result has also been predicted by the calculations, and it can be explained by certain peculiarities in the structure of the particles. The conjugation of the carbanionic charge with the cyano group in the cyclopropanecarbonitrile carbanion is greatly hindered by the considerable deviation (estimated at 56°) of the cyano group from the ring plane. The carbanionic charges of the carbanions studied are delocalized over the cyano groups (0.30–0.41 e − ), carbanionic centres (0.08–0.29 e − ) and hydrocarbon moieties (0.34–0.63 e − ).

IR studies in the substituted benzaldehyde series provide a new definition of sigma-plus constants of ionic substituents

Fourier-transform IR frequencies nu(C=O) and integrated intensities A(C=O) of the carbonyl groups of a series of benzaldehydes (53 compounds) have been measured in dimethyl sulphoxide. Excellent and satisfactory correlations have been found between nu(C=O) and sigma(+) substituent constants of the m- and p-substituted compounds. Diortho-substituted compounds deviate strongly from the correlation lines because of the steric ortho-effects mainly. sigma(+) constants of ionic substituents (10 examples) have proved satisfactorily valid in the series studied.

On the validity of the constants of ionic substituents. Substituent effects on the cyano stretching frequencies and intensities of trans-α-phenyl-β-arylacrylonitriles

Fourier-transform IR frequencies ν(CN) and integrated intensities A(CN) of the cyano groups of a series of trans-α-phenyl-β-arylacrylonitriles (51 compounds) have been measured. Both ν(CN) and the square roots of A(CN) of the neutral m- and p-substituted compounds (34 examples) have been found to correlate satisfactorily with σ1 substituent constants, as well as according to the equation of Yukawa-Tsuno. Diortho-substituted compounds deviate strongly from the correlation lines because of the steric ortho-effects mainly. σ+ (and other) constants of ionic substituents (seven examples) have proved satisfactorily valid in the series studied. The transmission coefficient of the CC double bond in the series has been estimated to be 0.7.

Vibrational assignment of benzil and its 18O substituted derivative

Abstract Vibrational spectra of benzil and benzil-18O in the solid phase and in the melt as well as in solution have been measured in the Raman (4000–20 cm−1) and the infrared (4000–100 cm−1). Their differential infrared linear dichroic spectra of oriented polycrystalline layers (4000–200 cm−1) have been also recorded and studied. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes. The presence of syn- and anti-phase vibrations of both phenyl rings is rediscussed. The previous assidnments of the in-plane and out-of-plane deformation of the carbonyl group and some fundamentals of bicarbonyl moiety are questioned and corrected.

LFER approach to the effects of neutral and anionic substituents on the νCO bands of ring_ substituted ethylbenzoates and acetophenones

Abstract Satisfactory correlations have been found between ν CO of ethylbenzoates and acetophenones (60 compounds, solvent DMSO) with σ + substituent constants. LFER approach has been checked to ν CO of ethylbenzoates and acetophenones with anionic substituents (17 compounds). σ + constants of anionic substituents, determined on the basis of nitrile infrared frequencies and intensities, have been found to be satisfactorily reliable in the series studied.

Infrared spectra and structure of carbanions: XVIII. A semiempirical study of carbanions of cyanoacetic acid derivatives1

Abstract The IR spectra of cyanoacetic acid, ethyl cyanoacetate and cyanoacetamide as well as those of related mono- and, whenever possible, dianions have been studied in dimethyl-sulphoxide (DMSO) and DMSO- d 6 .The observed nitrile and carbonyl absorption frequencies correlate linearly with the corresponding Wiberg bond indices given by CNDO/2 calculations with full geometry optimization. These calculations predict carbanionic structures throughout except in the case of the dinegative ion of cyanoacetamide, which could be considered as originating from the aminoacetylenic tautomer of NCCH 2 CONH 2 . Parallel MINDO/3 calculations, however, predict that the latter dianion is again a carbanion. This result is in reasonable agreement with normal coordinate calculations and the experimental isotopic shifts of vibrational frequencies of the dianion 15 NCCH − CONH − .

Infrared spectra and structure of carbanions : VIII. Mono- and di-alkali metal derivatives of some bis(cyanomethyl)arenes

Abstract Infrared spectral data were obtained for the mono- and di-alkali metal derivatives of 1,4-bis(cyanomethylbenzene, 1,4-bis(cyanomethyl)naphthalene and 9,10-bis(cyanomethyl)anthracene, as well as data for their electrochemically generated carbanions. It was found that the mono-alkali metal derivatives of the title nitriles exist as “free” carbanions in dimethyl sulphoxide and hexamethyl phosphoramide. The di-alkali metal derivatives are dicarbanions, and they can be considered as dianions of dicyano-quinodimethane and its polycyclic analogues.