A correlation of substituent effects with proton chemical shifts in aromatic tetrazolic acids

Abstract

The effect of substbents on the proton chemical shifts and spin-sph coupling constants in ortho-, meta-and para-substituted 5-pbenyltetrazQles (tetrazQiic acids) in DMSO-CH,CN (l:l,v/v) was studied. With the meta-and para-substituted compounds the additivity rnle of chemical shifts was obeyed, thereby enabling increments characterizing the effects of individual substituents in monosubstituted benzenes to be determined. By employing the Smith and Pro& eqnation, the chemical shifts of the aromatic protons were correlated with the F, R and Q substituent constants. The values of these coDstants are 1.02, -0.004 and 5.49, respectively, for the tetrazolyl substitaent.N M R studies on 5-substituted tetrazoles (tetrazolic acids) have so far been non-systematic and incomplete.'-'' Consequently, there have been no literature reports on correlations between the structures of these compounds and their NMR parameters. In continuation of our studies on tetrazolic acids we have investigated the effect of substituents on the chemical shifts of the benzene protons in 5-phenyltetrazoles. XCorreIations of chemical shifts with systematic variations in the structures of mono-and poly-substituted benzenes have been extensively studied, as they provide convenient model compounds due to the limited contribution of conformational effects. This was found to facilitate both empirical and theoretical correlations of the NMR parameters with such molecular parameters as electron density, electronegativity of the elements and Hammett-type constants. The effect of substituents on hydrogen," carbon12 and fluorine13 chemical shifts has been extensively characterized in many review articles. An essential feature of such considerations is also the additivity of the contribution of individual substituents to the chemical shifts in meta-and para -substituted benzene~.'~ The additivity rules have generally been found to be obeyed.A modified three-parameter correlation based on the Swain and Lupton equation'' has recently been suggested:where F and R are substituent constants characterizing field and resonance effects, respectively, and Q is a semiempirical parameter.'" * Author to whom correspondence should be addressed. EXPERIMENTAL Synthesis 0-, m-and p-Substituted 5-phenyltetrazoles weresynthesized by methods reported e1se~here.I~ All compounds were purified by crystallization until constant melting points were obtained. NMR spectraThe NMR spectra were recorded on a Tesla BS 487 C spectrometer (80 MHz), at approximately 18 "C for 9% w/v solutions in DMSO-CH3CN (1 : 1, v/v). Hexamethyldisiloxane was used as the external reference. The sweep width was 100 Hz/5 cm and the sweep time 500 s. spectral analysisThe analysis of the AA'BB' spin system was calculated by inspection of the spectrum. The remaining fourproton systems and the five-spin [ABI2C system of 5-phenyltetrazole were analysed by employing the ALGOL-1204 version of the computer programme LAOCN 323 (LAO-1 and LAO-2 versions). RESULTS ~The results reported in this paper involve the absorption...

Engineering a Cu‐MOF Nano‐Catalyst by using Post‐Synthetic Modification for the Preparation of 5‐Substituted 1H‐Tetrazoles

“…FT‐IR, 1 H and 13 C NMR spectroscopies and melting points were used to confirm the structure of the products. The results were also compared with the corresponding reported spectral data …”

“…The results were also compared with the corresponding reported spectral data. [40,43,60,[65][66][67][68][69][70][71][72][73][74] A plausible mechanism for the synthesis of tetrazole derivatives catalyzed by the nano-scale Cu-MOF is suggested in Scheme 3. Cu-MOF as Lewis acid plays a role in increasing the electrophilic character of the nitrile Compounds via coordination to nitrogen atoms (Step 1).…”

Application of mass spectrometry to the study of prototropic equilibria in 5-substituted tetrazoles in the gas phase; experimental evidence and theoretical considerations

“…This should result in elimination of either a nitrogen molecule or with a slightly lower probability of the NH2' radical. A further factor supporting this fragmentation sequence is represented by the E#) values for tautomers (2) With 5-methyltetrazole, E45(1) assumes a positive value after ionization, thus revealing the antibonding nature of the association of this pair of atoms (Table 3). The next most weakly associated pair of atoms in the radical ion is C(5)-N(1), followed by N(2)-N(3).…”

“…From considerations of the stability of the molecule from this standpoint, it can be concluded that tautomers (2) are more prone to fragmentation in the mass spectrometer than tautomers ( 1). An analysis of the numerical values of the total bicentre energy, Eap, of tautomer (2) show that the C(5)-N(4) C(5)-N(1) and N(2)-N(3) bonds should be the most readily broken. This should result in elimination of either a nitrogen molecule or with a slightly lower probability of the NH2' radical.…”

Luminescence of 5-phenyltetrazole and its Derivatives. Part I. Absorption and Fluorescence Spectra

“…In particular, acid-base equilibria [1,2], infrared absorption spectra [3], ultraviolet spectra [4,5], chemical shifts [6] and mass spectra [7] have been studied to afford in general satisfactory correlations with Hammett's substituent constants. Luminescence of these compounds has not yet been studied, however.…”