The temperature dependence of the Raman spectrum and gauche interactions of tri-N-butylamine: a conformational study

Abstract

M. S. LAMPREIA. Can. J . Chem. 65, 384 (1987).Raman spectra of tri-n-butylamine show pairs of bands whose temperature-dependent intensities clearly suggest their assignment to different conformers in simultaneous equilibria. These spectroscopic data are interpreted and correlated with structural information obtained from statistical analysis of gauche skeletal arrangements in tri-n-butylamine. The average numbers of gauche interactions in various tri-n-alkylamines are used to evaluate partial molal volumes which show excellent agreement with experimental data, thus imparting statistical meaning and usefulness to the concept of "average conformation".As the temperature decreases, the band at 904 cm-' in pure liquid tri-n-butylamine increases in intensity at the expense of the band at 880 cm-I. Both of these bands are ascribed to CH2 and CH3 rocking vibrations. In solution, the conformer represented by the band at 904 cm-' is favoured by polar solvents, whereas the conformer represented by the 860 cm-I band is favoured by non-polar solvents.The relative intensity changes with increasing temperature of the bands at 1456 and 1440 cm-is explained by an increase in the number of CH2 groups adjoining two gauche bonds and a decrease in the number of CH2 groups adjoining a trans and gauche bond.Temperature dependence of the relative intensities of bands in the CH stretching region suggest, by comparison with mono-and di-n-butylamine, that the increase in the number of alkyl chains around the nitrogen atom makes molecular packing less restrictive and unique, giving rise to mesophases, as the overall shapes of the molecules become more spherical. Chem. 65, 384 (1987).Les spectres Raman de la tri-n-butylamine prksentent des paires de bandes dont les intensitts dependent de la temperature; ces observations suggkrent clairement que l'on doit les attribuer a differents conformkres dans Cquilibres simultanks. O n interprkte ces donnCes spectroscopiques et on Ctablit une correlation avec les informations stmcturales obtenues a partir d'une analyse statistique des arrangements gauches du squelette de la tri-n-butylamine. On utilise les nombres moyens d'interactions gauches dans diverses tri-n-alkylamines pour Cvaluer les volumes molales partiels qui sont en bon accord avec Ies donnees expCrimentales; cette correlation permet d'attribuer une signification statistique et de dimontrer l'utilitk du concept de ccconformation moyenne n.Dans le cas de la tri-n-butylamine a 1'Ctat de liquide pur, une diminution de la temperature provoque une augmentation de l'intensitk de la bande A 904 cm-I, au detriment de la bande a 880 cm-I. On attribue ces deux bandes aux vibrations de balancement des CH2 et CH3. En solution, le conformere represent6 par la bande a 904 cm-I est favoris6 dans les solvants polaires alors que le conformkre represent6 par la bande a 860 cm-I est favoris6 par les solvants non polaires.On explique les changements d'intensitks relatives des bandes a 1456 et 1440 cm-', qui sont associCs a une augmentation de la tempCrature,...

Cavity-Enhanced Raman Scattering from 2D Hybrid Perovskites

“…23 Fundamental Raman modes of the BA cation fall in the R2 range (1200−1800 cm −1 ), which comprises the angular distortion of CH 2 , CH 3 , and NH 2 groups. 32,33 The observed Raman modes in our experiments in the R2 range at ≈1251 cm −1 correspond to CH 2 twisting, ≈1300 cm −1 to CH 2 wagging, ≈1458 cm −1 to a mixture of CH 2 scissoring vibration and CH 3 antisymmetric deformation, ≈1556 cm −1 to asymmetric NH 3 deformation, and ≈1584 cm −1 to NH 3 + degenerate deformation, while the mode at ≈1323 cm −1 marked with a blue asterisk is not reported in the literature (Figure S7). 23,29,32,33 A plausible explanation for the 1323 cm −1 mode could be that a strong interaction between BA and MA molecules of RP2 on gold with incoming photons has led to the splitting of mode at ≈ 1320 cm −1 into 1300 and 1323 cm.…”

“…32,33 The observed Raman modes in our experiments in the R2 range at ≈1251 cm −1 correspond to CH 2 twisting, ≈1300 cm −1 to CH 2 wagging, ≈1458 cm −1 to a mixture of CH 2 scissoring vibration and CH 3 antisymmetric deformation, ≈1556 cm −1 to asymmetric NH 3 deformation, and ≈1584 cm −1 to NH 3 + degenerate deformation, while the mode at ≈1323 cm −1 marked with a blue asterisk is not reported in the literature (Figure S7). 23,29,32,33 A plausible explanation for the 1323 cm −1 mode could be that a strong interaction between BA and MA molecules of RP2 on gold with incoming photons has led to the splitting of mode at ≈ 1320 cm −1 into 1300 and 1323 cm. −134 This further emphasizes that the enhanced light− matter interaction leads to an increase in the intensity of the nominally weak Raman modes of HOIP crystals in addition to the observation of hitherto unknown and unseen modes.…”

Theoretical study of internal rotational barriers of electrons donating and electrons withdrawing groups in aromatic compounds

“…In the experimental context, spectroscopic techniques with an emphasis on Raman spectroscopy, crystallography and microwave spectroscopy are the most used techniques to analyze the probable conformations of molecules of interest and then determine the values of rotational barriers [ 11 , 12 , 13 ]. On the other hand, computational studies have been frequently found in the literature, looking for elucidate the stereoelectronic effects responsible for the most stable conformations of different systems [ 14 , 15 ].…”