High Resolution Spectroscopic Studies of 1-(1-Naphthyl)ethylamine in S0 and S1: Exploring the Dependence of Circular Dichroism on Conformational Structure

Published

October 1, 2002

Author(s)

David F. Plusquellic, R J. Lavrich, T Petralli-Mallow, S Davis, T M. Korter, R D. Suenram

Abstract

Rotationally-resolved spectra of gas-phase samples of 1-(1-naphthyl) -ethylarnine (NEA) and amine deuterated forms have been obtained in the microwave and ultraviolet regions, with the isotopomers initially prepared in their zero-pointvibrational levels by cooling in pulsed jet and molecular beam supersonic expansions. A single parameter set that includes inertial parameters and ¹⁴ N nuclear quadrupole constants has accounted for nearly all transitions observed in the Fourier-transform microwave spectrum at 2 K and indicates the preponderance of only one geometrical isomer in the jet-cooled expansion. The rotational constants, dipole moment orientation and the amine hydrogen atom positions have been used to identify the conformation of the attached chiral group from among nine possible isomeric forms. The S₁ rotational constantsand transition moment orientation have been obtained from high resolution molecular beam data of the band origin at31771.56(2) cm^-1. Excited state Agas phase@ predictions from ab initio theory at the CIS/6-3 I G* level are compared with the observed S₁ results and with circular dichroism (CD) data obtained for solution phase samples of (S)-NEA incyclohexane. Distinguishing spectral features are found in the calculated CD spectral of the three lowest energy rotamers arising from rotation about the C-CH(NH₂)CH₃ bond. Best agreement with the experimental CD spectrum is found for the lowest energy jet-cooled structure and suggests the solvent only mildly perturbs the conformational and electronic structure of the chromophore. These results provide for rigorous benchmark tests of approximate theoretical models and further elucidate the importance of the conformational structure for determinations of absolute stereochemistry from CD spectra.

Citation

Chemical Physics

Volume

283

Issue

No. 1-2

Pub Type

Journals

Keywords

High resolution Spectroscopic, stereochemistry

Citation

Plusquellic, D. , Lavrich, R. , Petralli-Mallow, T. , Davis, S. , Korter, T. and Suenram, R. (2002), High Resolution Spectroscopic Studies of 1-(1-Naphthyl)ethylamine in S₀ and S₁: Exploring the Dependence of Circular Dichroism on Conformational Structure, Chemical Physics (Accessed April 25, 2024)