Bending vibrations in-plane

The v, i(b2) vibration featuring the asymmetric CC stretching vibration, which is strongly coupled with the asymmetric CH in-plane bending vibration (at 1061 cm- experimentally) is shifted by 20-25 cm towards lower frequencies, each time deuterium is incorporated in the molecule. The intensity ratio of V3 between the vs (ba) and the V4(a,) dominant feature is almost unchanged with deuteration. 

Figure 5. Pure torsional bands near the Si-So origin for three sixfold rotors as labeled. Band label my denotes a pure torsional transition from m = y in So to m = x in Si. The label bo denotes an increase from zero to one quantum of a low-frequency in-plane bending vibration.

Assignments have been made for a few of the more prominent and reliable in-plane bending vibrations. The vinyl group absorbs near 1416 cm-1 because of a scissoring vibration of the terminal methylene. The C—H rocking vibration of a cis-disubstituted alkene occurs in the same general region. 

In-plane bending vibrations Out-of-plane bending vibrations... 

The band near 700 cm. is assigned to the out-of-plane bending in since it shows an isotope shift, while the 650 cm. band is an in-plane bending mode without isotope effect. The weak band at 780 cm. may represent the remaining in-plane bending vibration. 

A few symbols are common to both NMR and IR literature one of these is S, meaning in NMR chemical shift and in IR an in-plane bending vibration. 

For the Zn salt, the broad absorbance between 1228 and 1240 cm is due to the asymmetric stretch of the SO anion. The symmetric stretch of the SOj anion appears as a shoulder at 1042 cm. A band at 1009 cm results from the in-plane bending vibrations of a benzene ring substituted with a metal sulfonate group. 

Tbe effect of hydration on the infrared spectrum of a 7.6 mole % H-SPS is shown in figure 3. After 19 hours the sample absorbed about 9% water, which corresponds to 9 moles H O per sulfonic acid group. This was accompanied by a ljirge decrease in the intensity of the absorbance band at 1176 cm and increases in the intensities of the bands at 1126 cm and 1007 cm. This result was expected, since upon hydration the acidic proton of the sulfonic acid is removed from the anion (1176 cm is characteristic of the S 0 symmetric stretch of the -SO.H and 1126 cm and 1007 cm are due to the ln-plane skeleton and the in-plane bending vibrations of a benzene ring with a SO, group attached). An absorbance at 1033 cm in the 19 hour sample is due to the symmetric stretch of the -SO and is further evidence of hydration Similarly, the decrease in intensity of the band at 1100 cm in the hydrated sample indicates that fewer -SO.H groups are present. 

The observed proton transfer times of the order of 50 fs have already been discussed in earlier work with respect to the importance of skeletal vibrations [16-18, 46[. It was proposed that a reduction in the distance between the proton donor and the acceptor results in a decrease in the energetic barrier between the enol-and the keto-form. At times when the barrier is suppressed the proton can tunnel or jump from its enol position to the keto site. In the case of HBO it was suggested that, in particular, the in-plane bending vibration modulates the donor-acceptor distance and thereby enables the proton movement [17]. This model was then applied to MS and to 2-(2 -hydroxyphenyl)-5-pheny]oxazole [18, 46]. However, due to insufficient time resolution of these experiments it was not possible to give experimental evidence for this model. 

Further transitions in the hydrogen bond stretch, donor torsion overtone, and in-plane bend vibrations were analyzed in [03Keul]. 

The principal infrared bands of rhodotorulic acid were at 3190,3095,2870,1682,1594, 1467,1447,1430,1339,1216,1164,969,827,797,and777crn i. The 1682 cm" band was assigned to amide I absorption. Characteristics of the cis-peptide bonds of the ring included a lack of N—H stretching bands higher than 3250 cm , lack of any bands in the amide II region, and presence of the in-plane-bending vibration near... 

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