The rotational spectrum and molecular geometry of the cyclopropane–HF dimer

Abstract

Four isotopic species of a hydrogen-bonded dimer formed between cyclopropane and HF have been observed through assignment of their rotational spectra using a pulsed, Fourier-transform microwave spectrometer in which a gas mixture is pulsed into an evacuated Fabry–Perot cavity. The geometry of the dimer has unambiguously been shown to have HF perpendicular to the cyclopropane edge and in the plane of the ring. HF, on average, lies on the C2 symmetry axis of the dimer which is additionally the a principal axis. Hyperfine structure due to the spin–spin interaction in HF and DF was resolved as well as the hyperfine structure due to the nuclear quadrupole moment of deuterium in the cyclopropane–DF species. The following spectroscopic constants have been obtained for the cyclopropane–HF species: The rotational constants are A = 19 948(60), B = 2753.706(2), and C = 2539.115(2) MHz, the HF spin–spin constant is 121(43) kHz, and the centrifugal distortion constants are DJ = 5.08(27) and DJK = 43.5(36) kHz.

Accurate dissociation energies of two isomers of the 1-naphthol⋅cyclopropane complex

“…The H atom of the OH group is nearly 0.4 Å closer to the nearest CC bond than the H atoms in the face-on isomer. This OH · · · cyclopropane bonding motif is very similar to that of the F-H · · · cyclopropane complex, 29 and is also similar to the crystallographically observed CH · · · π (alkene) interaction geometries. 24 The B ′ structure can be converted to B by translating the cyclopropane in-plane across the naphthalene ring and rotating it by ∼60 • .…”

“…On the other hand, the OH group of 1-NpOH may act as an H-donor to a C-C bond of cyclopropane, analogous to the structure of F-H·cyclopropane. 29 Below, we show that both isomers are formed; we can determine the D 0 (S 0 ) values of both isomers separately within ±3 cm −1 and ±10 cm −1 , making these measurements among the most accurate experimental intermolecular dissociation energies to date. 9,[30][31][32] These measurements on isomers of the same complex represent useful benchmarks and a special challenge for theory.…”

“…24 However, gas-phase spectroscopic evidence of H-bonded cyclopropane is rather sparse. [27][28][29] A paradigmatic example is the F-H·cyclopropane complex, in which the HF moiety forms an H-bond to the C-C bond of cyclopropane. 29 In 1-NpOH·cyclopropane, a structure can occur with cyclopropane adsorbed to one face of the naphthalene π-system, giving rise to CH · · · π interactions.…”

“…[27][28][29] A paradigmatic example is the F-H·cyclopropane complex, in which the HF moiety forms an H-bond to the C-C bond of cyclopropane. 29 In 1-NpOH·cyclopropane, a structure can occur with cyclopropane adsorbed to one face of the naphthalene π-system, giving rise to CH · · · π interactions. On the other hand, the OH group of 1-NpOH may act as an H-donor to a C-C bond of cyclopropane, analogous to the structure of F-H·cyclopropane.…”

The microwave spectrum of cyclopropane · ammonia. A novel structure for cyclopropane complexes

“…(CYC) complexes, such as CYC-HCl [I], CYC-HF [2], CYC-HCN [3], and CYC-Hz0 [ 4 1, have been thoroughly investigated by Fourier-transform microwave (FTMW) spectroscopy in order to determine their structure. In each case the HX lies in the heavy atom plane and is hydrogen bonded to the center of one of the C-C bonds.…”