A Microwave and Quantum Chemical Study of Cyclopropanethiol

Abstract

The microwave spectra of cyclopropanethiol, C(3)H(5)SH, and one deuterated species C(3)H(5)SD, have been investigated in the 20 - 80 GHz frequency range. The spectra of the ground vibrational state and of three vibrationally excited states of the parent species of a conformer which has a synclinal ("gauche") arrangement for the H-C-S-H chain of atoms, was assigned. The H-C-S-H dihedral angle is 76(5)° from synperiplanar (0°). The b-type transitions of the ground and of the vibrationally excited states of the parent species were split into two components, which is assumed to arise from tunneling of the proton of the thiol group between two equivalent synclinal potential wells. No splitting was resolved in the spectrum of C(3)H(5)SD. The tunneling frequency of the ground vibrational state of C(3)H(5)SH is 1.664(22) MHz. The tunneling frequency of the first excited-state of the C-S torsion is 52.330(44) MHz, whereas this frequency is 26.43(13) and 3.286(61) MHz, respectively, for the first excited states of the two lowest bending vibrations. The dipole moment of the ground vibrational state of the parent species is μ(a) = 4.09(5), μ(b) = 2.83(11), μ(c) = 0.89(32), and μ(tot) = 5.06(16) × 10(-30) C m. The microwave study has been augmented by high-level density functional and ab initio quantum chemical calculations.

Internal Rotation of Methylcyclopropane and Related Molecules: Comparison of Experiment and Theory

“…CCSD/cc-pVTZ values top row. MP2/cc-pVTZ values bottom row in parentheses and in italics. c Reference . d Reference . e Reference . f Reference . g Reference . h MP2/aug-cc-pVTZ values ref . i Reference . j MW, ref . …”

“…The Møllendal group has reported the microwave spectrum of cyclopropanethiol (CP–SH) and found that the molecule has two equivalent synclinal conformers. They also reported the ground-state torsional energy level splitting to be 1.664 MHz.…”

“…Table 6 compares the calculated transition frequencies for the three functions, and it can be seen that the refined function fits the experimental data very well. The Møllendal group 24 has reported the microwave spectrum of cyclopropanethiol (CP−SH) and found that the molecule has two equivalent synclinal conformers. They also reported the ground-state torsional energy level splitting to be 1.664 MHz.…”

“…In the present study we performed high-level ab initio calculations for each of these molecules and also for cyclopropanol (CP–OH) and cyclopropanethiol (CP–SH) to assess how well the theoretical calculations do for predicting the barriers and potential energy functions. Experimental microwave results have been previously reported for CP–OH and CP–SH, and low-level theoretical calculations were also performed on CP–OH . The far-infrared spectrum of cyclopropylamine (CP–NH 2 ) has previously been studied by Kalasinsky and co-workers, and a potential energy function was determined.…”

Synthesis, Microwave Spectrum, and Conformational Equilibrium of Propa-1,2-dienethiol (H2C═C═CHSH)

“…The present study also represents an extension of our recent investigations of the conformational properties of thiols such as 3-butyne-1-thiol (HSCH 2 CH 2 CCH), ( Z )-3-mercapto-2-propenenitrile (HSCHCHCN), cyclopropanethiol (C 3 H 5 SH), and 2,2,2-trifluoroethanethiol CF 3 CH 2 SH, using MW spectroscopy augmented with quantum chemical calculations.…”