banner image
No data available.
Please log in to see this content.
You have no subscription access to this content.
No metrics data to plot.
The attempt to load metrics for this article has failed.
The attempt to plot a graph for these metrics has failed.
Conformers of β-aminoisobutyric acid probed by jet-cooled microwave and matrix isolation infrared spectroscopic techniques
Rent this article for


Image of Scheme 1.
Scheme 1.

Schematic representation of BAIBA with indication of its 4 internal torsional degrees of freedom which can give rise to conformational isomers.

Image of FIG. 1.
FIG. 1.

The 19 lowest energy conformers of BAIBA. Conformers A 1 , A 2 , B 1, and B 2 were observed experimentally by microwave spectroscopy in this study.

Image of FIG. 2.
FIG. 2.

MP2/6-311++G(d,p) calculated potential energy profile for interconversion between conformers B 2 and B 3. The calculated B 3B 2 energy difference ( ) is 1.9 kJ mol−1, while the zero-point corrected MP2/B3LYP/6-311++G(d,p) energy difference ( ) is 1.6 kJ mol−1 (see also Table I ). The barrier to conformational isomerization presented in the figure does not take into account the zero-point corrections.

Image of FIG. 3.
FIG. 3.

Broadband CP-FTMW rotational spectrum of BAIBA in the 6–18 GHz region. Top insets: (left) detail of the CP-FTMW spectrum showing the feature ascribed to the 303-212 transition for conformer B 1; (right) high-resolution LA-MB-FTMW spectrum of the same transition, showing the quadrupole components labeled for conformer B 1.

Image of FIG. 4.
FIG. 4.

Infrared spectrum of BAIBA in a N2 matrix at 13 K.

Image of FIG. 5.
FIG. 5.

Difference IR spectrum (near-IR irradiated BAIBA:N2 matrix at 6930 cm−1 minus as-deposited matrix) (top), compared with the difference simulated spectrum for conformers A 1 (bands pointing up) and B 1 (down) (bottom). In the simulated spectrum, bands were represented by Lorentzian profiles having a full-width at half maximum (FWHM) of 2 cm−1 centered at the calculated frequencies scaled by 0.993 (below 1650 cm−1), 0.965 (above 1650 cm−1) and 0.945 (νO–H and νNH2 stretching modes). Note that even after the applied scaling the calculated νO–H frequency in the O–H⋯N hydrogen bonded conformer A 1 is considerably overestimated (as evidenced by the arrow). The most characteristic new bands emerging upon irradiation are marked with a red asterisk, and are ascribed to conformer D 1 (see text and Figure 6 ).

Image of FIG. 6.
FIG. 6.

Schematic representation of the observed near-IR induced conformational isomerizations of BAIBA isolated in a N2 matrix upon irradiation at 6930 cm−1.

Image of FIG. 7.
FIG. 7.

Difference spectra of BAIBA monomers isolated in N2 matrix at 13 K, in the B 1 νO–H (left) and νC=O (right) stretching regions. The spectra shown correspond to consecutive irradiations. Profile in black is obtained after subtracting spectrum of the freshly deposited matrix from that obtained after irradiation 1 (λ = 6939 cm−1); profile in blue is the result of subtraction of the spectrum in black from the one obtained after irradiation 2 (λ = 6920 cm−1); and the one in red is obtained after subtracting the blue spectrum from the one obtained as a result of irradiation 3 (λ = 6930 cm−1).


Generic image for table
Table I.

Calculated relative energies (zero-point corrected; ΔEo) and Gibbs free energies at room temperature (RT = 298.15 K) (ΔGo), and predicted populations for the lowest energy conformers of BAIBA. a

Generic image for table
Table II.

Experimental spectroscopic parameters for the four observed conformers of BAIBA compared with those predicted at the MP2/6-311++G(d,p) level of theory. a


Article metrics loading...


Full text loading...

This is a required field
Please enter a valid email address
752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Conformers of β-aminoisobutyric acid probed by jet-cooled microwave and matrix isolation infrared spectroscopic techniques