V. A. Lopyrev

Specific effect of pentafluorophenyl fragment on electronic state of carbonyl group in ketones, amides, and hydrazides containing a pentafluorophenyl group

Conclusions1.The effect of the C6F5 group on the ΝC=0 frequency of C6F5COR compounds depends on the structural features of the R fragment; for ketones, amides, and hydrazides there is steric inhibition of resonance in the C6F5CO group and an increase in the role of the inductive effect from C6F5.2.In N-dimethylpentafluorobenzamide the decrease in resonance is compensated by p,π-conjugation in the CON group, and the inductive effect of the C6F5 ring appears to be weaker than in pentafluoroacetophenone.3.The presence of the second nitrogen atom and the change in relative orientation of the unshared electron pair when affected by substituents at N1 and N2 in pentafluorobenzahydrazide molecules leads to an increase in the torsion angle in C6F5-CO in comparison to N-dimethylpentafluorobenzamide, which increases the -I effect of C6F5 on ΝC=0 in pentafluorobenzhydrazides.

IR spectroscopic study of substituent effects in N,N-dimethylhydrazides of aromatic acids

ConclusionsAn IR spectroscopic study showed that the νC=0 values in the spectra of N,N-dimethylhydrazides of aromatic acids, RCONHN(Me)2, correlate linearly with a regression equation obtained for the unsubstituted hydrazides of aromatic acids, RCONHNH2. This dependence differs significantly from that for N-methyl-N-aroylhydrazines, in which π,π-conjugation in the RC(O)N group is more pronounced.

Spectroscopic study of the reaction of acids with 1-fluoroacetyl-1,2-dimethylhydrazines

Conclusions1.The reaction of 1-fluoroacyl-1,2-dimethylhydrazides with phenol and trifluoroacetic acid in a medium of CCl4 and MeCN takes place with the formation of a molecular H complex, and the oxygen atom in the C=O group is the H bond acceptor in the hydrazides.2.Decomposition of the three-component associates of 1-fluoroacyl-1,2-dimethylhydrazides and protonation of the nitrogen atom in a medium of MeCN take place in the reaction of these molecules with perchloric, picric, and hydrochloric acids.3.The ratio of the free forms and the forms of the hydrazides protonated with respect to the N2 atom is dependent on the inductive properties of the R substituent in the acyl fragment. The smallest contribution of the protonated form is observed with R=CF3, and the strength of the NH...N2 bond is highest.

Electron-impact fragmentation of mono- and diacylhydrazines of fluorocarboxylic acids

Abstract The mechanism of electron-impact dissociative ionization of mono- (I) and diacylhydrazines (II) of fluorocarboxylic acids RC(O)NHNHR 1 (I) and RC(O)NHNR 1 C(O)R (II) with RCH 3 , CH 2 F, CHF 2 , CF 3 , C 2 F 5 , C 3 F 7 , C 4 F 9 , C 6 F 13 ; R 1 H, CH 3 , C 2 H 5 , C 3 H 7 , iC 3 H 7 , C 9 H 19 , C 6 H 5 has been studied. The fragmentation of (I) with R 1 H involves direct cleavage of C(O)C and C(O)N bonds. The accumulation of fluorines in the molecule increases the portion of dissociates at the C(O)C bond and, starting from R 1 C 2 F 5 , no fragmentation at the C(O)N bond occurs. When an alkyl group is introduced into the hydrozine fragment some arrangements involving NN bond cleavage become prevailing processes. Elongation of perfluoroalkyl groups does not affect much the molecular ion fragmentation, the mass spectra pattern being dependent on only the size and character of the substituent R 1 attached to the nitrogen atom. The fragmentation of fluorine-containing diacylhydrazines (II) proceeds analogously to that of (I) with R 1 H, independently of substituent R 1 . The major contribution to the total ion current is from ions generated by dissociation of the perfluoroacyl fragment. The main trends in dissociation of parent ions and fragments have been considered and compared with fragmentation of some non-fluorinated analogs. Some mechanisms for the rearrangement processes have been suggested.

Substitutent effects in hydrazides of fluorocarboxylic acids

Abstract Intramolecular interaction in hydrazides of fluorocarboxylic acids, R 1 F CON 1 R 2 N 2 R 3 R 4 (R 1 F = fluoroalkyl and pentafluorophenyl substituents, R 2 ,R 3 ,R 4 = H, Alk) was studied by UV and IR spectroscopy. The long wavelength absorption (230–250 nm) in the UV spectra of alkanefluorocarboxylic acids is mainly caused by electron transitions in NNCO groups. The absorption corresponds to the p,π-conjugation and interaction of lone electron-pairs in the molecule. Different substitution at nitrogen atoms changes the electron transition energy. The νCO band intensity and frequency reflect the change in the resonance interaction in CON group. The ability of hydrazides to self-association via NHCC and NHN bonds also depends on the substitution in the NN fragment. A remarkable stability of fluoroacyl-N 1 ,N 2 -dimethylhydrazine associates present as NHN bonded trimer structures even in the gas phase has been established. At the same time, the relative basicity of the oxygen atom of the compounds studied (Δν OH) is poorly susceptible towards substitution at the nitrogen atom. The Δν OH value is considerably lower in fluorocarboxylic hydrazides than that of their non-fluorinated analogs. The intramolecular mutual effect of C 6 F 5 and CONN groups in pentafluorophenylhydrazides manifests itself by lower π-order of the C 6 F 5 CO bond and higher torsion angle ζ as compared with hydrocarbon analogs.

Influence of substituents on IR and UV spectral parameters of 1-methylhydrazides of aromatic acids

Conclusions1.The absorption bands In the UV spectra of 1-methylhydrazides of aromatic acids have been assigned to specific types of electronic transitions. It has been shown that the amide fragment plays the decisive role in determining the nature of the electronic transitions of these molecules.2.It has been shown that strong intermolecular hydrogen bonds NH... N are present in these compounds. The center of basicity in the 1-aroyl-1-methylhydrazines when they interact with phenol is the oxygen atom of the C=O group. The independence of its electron-donor strength from any influence of the para substituent on the aromatic ring and from the frequency νC=O in the IR spectra indicates a partial breakdown of conjugation of the benzene ring and the carbonyl group in the molecules.

Hydrogen bonds in 1-acyl-1,2-dimethylhydrazines of fluorocarboxylic acids

Conclusions1.The molecules of 1-acetyl-, 1-trifluoroacetyl-, and 1-difluoroacetyl-1,2-dimethylhydrazines form hydrogen bonds, which remain in dilute solutions and, partly, in the gaseous state.2.Associations in 1-acetyl-1,2-dimethylhydrazine are evidently realized with the participation both of the unshared electron pairs of the oxygen atom and of the nitrogen at position 2.3.The introduction of fluorine atoms into the acyl fragment of the hydrazide molecule leads to the preferential formation of intermolecular hydrogen bonds of the N-H⋯N type.4.The low probability of the formation of an intramolecular hydrogen bond of the N-H⋯ O=C type was demonstrated.

Spectroscopic investigation of the intramolecular effects in the hydrazides of fluoro-substituted carboxylic acids

Conclusions1.The introduction of a phenyl or alkyl substituent at the β-nitrogen atom in the hydrazides of carboxylic acids and their fluorinated analogs leads to a trans orientation of the unshared pairs of electrons on the nitrogen atoms.2.The influence of fluorine atoms on the electronic state of the C=O group in molecules of 1-acyl-2-alkylhydrazines and 1-acyl-2-phenylhydrazines is due to the inductive effect of the substituent R and to the possibility of stabilization by the intramolecular NH...F hydrogen bond.3.The greatest electronic effect of a fluoroalkyl substituent on a hydrazide fragment is realized in the acylhydrazines and 1-acyl-2-phenylhydrazines.

Electronic absorption spectra of 3-chloro- and 3-amino-1,2,4-triazole derivatives

The manifestation of acid-base interactions in the electronic absorption spectra of 32 1,2,4-triazole derivatives was studied. Ionization of the heteroring does not have a substantial effect on the energies of the electron transitions of 3-chloro-5-substituted 1,2,4-triazoles but causes changes in the extinctions of the absorption bands of 3-amino-5-substituted triazoles.

Calculation of the electron structures and electronic spectra of 3-chloro- and 3-amino-1,2,4-triazole derivatives

Abstract3-Chloro- and 3-amino-1,2,4-triazole derivatives were subjected to a theoretical study by means of quantum-chemical calculation by the Pariser-Parr-Pople method. The experimentally observed electron transitions were assigned. The Cl atom and the NH2 group in the 3 position of 1,2,4-triazole subject the electron system of the heteroring to substantial perturbation.