We report a free jet microwave absorption study of 2-amino-1-phenylethanol and 2-methylamino-1-phenylethanol which are analogues of noradrenaline and adrenaline respectively. The conformational properties of the molecules have already been investigated [1,2] using different laser based techniques coupled with high level ab initio calculations. Band contour analysis allowed the structural assignment subsequently confirmed by double resonance experiments and quantum chemical calculations. Inspired by these studies and with the aim of obtaining more structural information from the rotational constants and eventually observe in the spectrum fine structures due to internal motions in the molecules, we performed our free jet microwave study. The spectra were recorded in different expansion conditions and with different carrier gases. Several conformational species were detected in the spectrum recorded with He and from the experimental rotational constants we could determine the main structural parameters. Our assignments basically confirm the ones already made in the previous studies, where two conformers for the analogue of noradrenaline and three for the analogue of adrenaline were observed. All conformational species are mainly stabilized by non bonded interactions and the principal forces modelling the shape of the flexible side chain are an intramolecular hydrogen bond between the hydroxyl and the amino group and a second interaction between the amino or methylic hydrogen and the  cloud. [1] Graham, R.J., Kroemer R.T., Mons M., Robertson E.G., Snoek L.C. and Simons J.P., J. Phys. Chem. A 103 (1999) 9706. [2] Butz P., Kroemer R.T., Macleod N.A., Robertson E.G. and Simons J.P., J. Phys. Chem. A 105 (2001) 1050.
Free jet microwave spectroscopy and conformational properties of Noradrenaline and Adrenaline analogues.
MELANDRI, SONIA;
2004
Abstract
We report a free jet microwave absorption study of 2-amino-1-phenylethanol and 2-methylamino-1-phenylethanol which are analogues of noradrenaline and adrenaline respectively. The conformational properties of the molecules have already been investigated [1,2] using different laser based techniques coupled with high level ab initio calculations. Band contour analysis allowed the structural assignment subsequently confirmed by double resonance experiments and quantum chemical calculations. Inspired by these studies and with the aim of obtaining more structural information from the rotational constants and eventually observe in the spectrum fine structures due to internal motions in the molecules, we performed our free jet microwave study. The spectra were recorded in different expansion conditions and with different carrier gases. Several conformational species were detected in the spectrum recorded with He and from the experimental rotational constants we could determine the main structural parameters. Our assignments basically confirm the ones already made in the previous studies, where two conformers for the analogue of noradrenaline and three for the analogue of adrenaline were observed. All conformational species are mainly stabilized by non bonded interactions and the principal forces modelling the shape of the flexible side chain are an intramolecular hydrogen bond between the hydroxyl and the amino group and a second interaction between the amino or methylic hydrogen and the cloud. [1] Graham, R.J., Kroemer R.T., Mons M., Robertson E.G., Snoek L.C. and Simons J.P., J. Phys. Chem. A 103 (1999) 9706. [2] Butz P., Kroemer R.T., Macleod N.A., Robertson E.G. and Simons J.P., J. Phys. Chem. A 105 (2001) 1050.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
