FOURIER TRANSFORM MICROWAVE SPECTRA OF N-METHYLFORMAMIDE
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Date
2002
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
In order to understand the dynamical behavior of the peptide bond in ``peptide molecules: $X-CONH-Y$'', we have chosen N-methylformamide $(N-MFA)$ as a simplest system with $X = H$ and $Y = CH_{3}$. The microwave spectrum of the most stable trans form of N-MFA was studied by Fantoni and $Caminati,^{a}$ who assigned and analyzed only the A state of the $CH_{3}$ internal rotation and thus reported an estimated potential barrier $V_{3}$. Kitano and $Kuchitsu^{b}$ determined the molecular structure of trans $N-MFA$ by using electron diffraction, but they could not detect the higher energy cis conformer. We report here the rotational spectrum of both the trans and cis forms of $N-MFA$ using $FTMW$ spectrometers at NIST and KAIT, in the frequency region from 5 to 36 GHz, with either $Ne$ or $Ar$ as a buffer gas in a reservoir nozzle maintained at about $50^{\circ}$C. We confirmed the assignment of Ref.a for the trans A state and extended the observation to low-J transitions. The spectra of four trans isotopomers $^{13}C, ^{15}N$, and $^{18}O$ were observed to derive an $r_{s}$ structure, which is in good agreement with the electron diffraction and ab initio results. The $V_{3}$ value of trans is approximately $60 cm^{-1}$, which is 4.5 times smaller than the value of cis form which was determined to be $279 cm^{-1}$.
Description
$^{a}$A. C. Fantoni and W. Caminati J. Chem. Soc. Faraday Trans. 92, 342 (1995).$^{b}$M, Kitano and K. Kuchitsu Bull. Chem. Soc. Jpn. 47, 631 (1974).
Author Institution: Department of Applied Chemistry, Kanagawa Institute of Technology; Department of Applied Chemistry, National Institute of Standards and Technology; Department of Applied Chemistry, The Graduate University for Advanced Studies
Author Institution: Department of Applied Chemistry, Kanagawa Institute of Technology; Department of Applied Chemistry, National Institute of Standards and Technology; Department of Applied Chemistry, The Graduate University for Advanced Studies