A Study of 2-Iodobutane by Rotational Spectroscopy

Rotational transitions belonging to 2-iodobutane (sec-butyl-iodide, CH₃CHICH₂CH₃) were measured over the frequency range 5.5-16.5 GHz via jet-pulsed Fourier transform microwave spectroscopy. The complete nuclear quadrupole coupling tensor of iodine, was obtained for the gauche (g)-, anti (a)-, and gauche′ (g′)-conformers as well as the four ¹³C isotopologues of the gauche species. Rotational constants, centrifugal distortion constants, quadrupole coupling constants, and nuclear spin-rotation constants were determined for each species. Changes in of the iodine nucleus, resulting from conformational and isotopic differences, are discussed. Isotopic substitution of g-2-iodobutane allowed for an r_s structure to be determined for the carbon backbone. Additionally, isotopic substitution in conjunction with an ab initio structure allowed for a fit of various r₀ structural parameters belonging to g-2-iodobutane.