Rotational spectra and conformer geometries of 2-fluorophenol and 3-fluorophenol

Abstract

The ground states of 2-fluorophenol (2FPh) and 3-fluorophenol (3FPh) and their 13 C isotopologues were investigated using Fourier transform microwave (FTMW) spectroscopy in the range of 6 to 26 GHz. Two planar conformers were observed for 3FPh, corresponding to cis and trans orientations of OH relative to F, while only the cis conformer of 2FPh was detected.The rotational constants determined were used to derive substitution (rs) and effective ground state (r0) structures of the lowest energy conformer of each compound: cis-2FPh and trans-3FPh.Geometry optimization at the MP2/6-311++G(2d,2p) level provided equilibrium (re) structures which are in close agreement with the experimental parameters. The derived structures along with results from natural bond orbital (NBO) calculations provide evidence of an intramolecular interaction in cis-2FPh between the fluorine atom and OH moiety that stabilize this conformer by 0.72 kcal/mol. .

Determination of the “Privileged Structure” of 8‐Hydroxyquinoline

“…The distance between H and N is 2.0738 Å, much smaller than the sum of the van‐der‐Waals radii of N and H (2.75 Å) which is commonly taken as a measure of H‐bond strength. The equivalent distance of H−F in cis 2 fluorophenol [35] is 2.212 Å compared with a vdW radii sum of 2.57 Å, indicating a stronger non‐covalent interaction in 8‐HQ.…”

“…There are limited opportunities to compare the structural parameters with the experimentally determined structures of similar molecules given the paucity of data for similar systems. A comparison with a similar structural arrangement, that of 2‐hydroxy pyridine, [33] shows essentially the same C−O−H angle (106 degrees versus 105.5 degrees for 8‐HQ) This angle is much smaller than that of 108.8 degrees in phenol [34] and cis‐2‐fluorophenol, where H bonding with the F reduces it to 108.1 degrees [35] . It appears that the N in 2‐hydroxy pyridine and 8‐HQ comes into play to reduce the C−O−H angle.…”

“…A comparison with a similar structural arrangement, that of 2hydroxy pyridine, [33] shows essentially the same CÀ OÀ H angle (106 degrees versus 105.5 degrees for 8-HQ) This angle is much smaller than that of 108.8 degrees in phenol [34] and cis-2fluorophenol, where H bonding with the F reduces it to 108.1 degrees. [35] It appears that the N in 2-hydroxy pyridine [35] is 2.212 Å compared with a vdW radii sum of 2.57 Å, indicating a stronger non-covalent interaction in 8-HQ.…”

Rotational Spectroscopic and Ab Initio Investigation of the Rotamer Geometries of 2-Fluoroanisole and 3-Fluoroanisole

“…10,11 In addition to characterizing the overall structures of increasingly complex molecules, modern high resolution Fourier transform microwave (FTMW) spectroscopy has proved invaluable for probing very subtle geometric changes that accompany the addition of a substituent in an organic compound. For example, the fluorinated ring compounds of benzene, [12][13][14] pyridine, 15,16 and cyanobenzene, 17 have served as simple prototypes in building a detailed understanding of the influence of fluorine on the ring geometry while studies of fluorinated phenol, 18 thiophenol, 19 and benzaldehyde 20 have extended this to also include the impact of fluorine on intramolecular interactions and conformer distributions. In these ring compounds, the largest geometric changes induced by fluorination are found in close proximity to the substitution site and typically involve an increase in the ring angle at that site by 3-4 o and a shortening of the adjacent C-C bonds by 0.005-0.010 Å.…”

Synthesis, Electronic and Spectral Properties of New 1,3,4-Thiadiazole Compounds and the Spectral Analysis of Their Conformers Using Density Functional Theory

“…However, conformational analyses have mostly been used to compare experimental and theoretical data and to understand the nature of experimental results. [15][16][17][18][19][20][21][22][23] Here we have considered the question, 'What is the relationship between the electronic and spectral properties of the conformers of a compound, and does the relationship have distinctive characteristics?' We also investigated how molecular conformations affected the minimum molecular energy, frontier molecular orbital (FMO) energies, some electronic parameters such as chemical hardness and electronegativity, and the UV, IR and NMR spectra.…”