Browsing by Author "Bugalho, Susana C. S."
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- Low temperature matrix-isolation and solid state vibrational spectra of 5-chlorotetrazolePublication . Bugalho, Susana C. S.; Serra, Arménio C.; Lapinski, L.; Cristiano, Maria Lurdes Santos; Fausto, R.The vibrational spectra of 5-chlorotetrazole (CN4HCl) isolated in an argon matrix (T ¼ 8.5 K) and in the solid state (at room temperature) were studied. The infrared spectrum of monomers of 5-chlorotetrazole isolated in an argon matrix agrees well with the spectrum predicted theoretically (DFT(B3LYP)/6-31G*) for the 2Htautomer of the compound. The bands assigned to the 1H-tautomer appear in the experimental spectrum as very low intensity features. Based on the relative intensities of the bands in the spectra of the 1H- and 2Htautomers, the relative amount of the first tautomer in this matrix can be estimated as 1%. Three matrixes were deposited with different nozzle temperatures and the enthalpy difference between the tautomers DH ¼ 8.0 kJ mol 1 was estimated using the Van’t Hoff relation. The internal energy difference between the two tautomers was predicted theoretically (DFT B3LYP/6-31G*) as 12.6 kJ mol 1. This is in reasonable agreement with experimental observations. In the crystalline phase, this compound exists in its 1H-tautomeric form. Accordingly, the IR spectrum of polycrystalline 5-chlorotetrazole is well reproduced by the spectrum predicted theoretically for the 1H- tautomer.
- Low temperature matrix-isolation and solid state vibrational spectra of tetrazolePublication . Bugalho, Susana C. S.; Maçôas, Ermelinda M. S.; Cristiano, Maria Lurdes Santos; Fausto, R.Infrared spectra of tetrazole (CN isolated in an argon matrix (T \10 K) and in the solid state (at room 4H2) temperature) were investigated. In the crystalline phase, tetrazole exists in its 1H-tautomeric form and new assignments of the vibrational spectra (both infrared and Raman) of this phase are presented. The infrared spectrum of the matrix-isolated monomeric form of tetrazole is now reported and assigned for the Ðrst time, showing essentially the expected signature of the 2H-tetrazole tautomer. From relative intensities of the infrared bands ascribable to the two tautomers, the amount of the 1H-tautomer in the argon matrix was estimated to be ca. 10% of the most stable tautomer. Assuming that gas-phase relative populations of the two tautomers could be efficiently trapped in the argon matrix during deposition, the energy di erence between 1H- and 2H-tetrazole (*E was then obtained. The experimental value, kJ mol~1, 1Hh2H) *E1Hh2H\6.95^1.50 now determined for the Ðrst time, compares fairly well with the theoretical predictions for the molecule in vacuum (e.g., the zero point vibrational energy corrected energy di erence obtained at the B3LYP/6È31G* level of theory is 9.96 kJ mol~1).
- Vibrational spectra and structure of 1-phenyltetrazole and 5-chloro-1-phenyltetrazolePublication . Bugalho, Susana C. S.; Lapinski, L.; Cristiano, Maria Lurdes Santos; Frija, L.; Fausto, R.Infrared spectra of 1-phenyltetrazole (C7N4H6) and 5-chloro-1-phenyltetrazole (C7N4H5Cl) isolated in argon matrixes (T ¼ 8 K) and in the solid state (at room temperature) were studied. DFT(B3LYP)/6-31G* calculations predict the minimum energy conformation of 1-phenyltetrazole as being non-planar, with the two rings (phenyl and tetrazole) twisted by 298. For 5-chloro-1- phenyltetrazole, the optimized dihedral angle between the two rings is larger (488). The theoretically calculated IR spectra of both compounds fit well the spectra observed experimentally. This allowed a reliable assignment of observed IR absorption bands.