Rotational spectra of o-, m-, and p-cyanophenol and internal rotation of p-cyanophenol

Abstract

Rotational spectra of p-, m-, and o-cyanophenol have been measured in the range of 10.5-21 GHz and fit using Watson's A-reduction Hamiltonian coupled with nuclear quadrupole coupling interaction terms for the (14)N nuclei. Ab initio calculations at the MP2/6-311++G(d,p) and CCSD(T)/6-311++G(d,p) levels predict the cis conformers of m- and o-cyanophenol to be more stable than the corresponding trans conformers. A natural bond orbital analysis of the hydrogen bonding interaction in o- and m-cyanophenol revealed an intramolecular hydrogen bond that preferentially stabilizes the cis conformer of o-cyanophenol but there was no evidence of hydrogen bonding interactions in cis m-cyanophenol. We recorded 25 a- and b-type rotational transitions for cis o-cyanophenol; the rotational constants are A = 3053.758(2) MHz, B = 1511.2760(3) MHz, and C = 1010.7989(2) MHz. The trans conformer of o-cyanophenol was not observed. We recorded 14 a- and b-type rotational transitions for cis m-cyanophenol and 16 a- and b-type rotational transitions for trans m-cyanophenol. The rotational constants are A = 3408.9200(2) MHz, B = 1205.8269(2) MHz, and C = 890.6672(1) MHz and A = 3403.1196(3) MHz, B = 1208.4903(2) MHz, and C = 891.7241(2) MHz for the cis and trans species, respectively. Rotational transitions of the p-cyanophenol monomer are split due to the internal rotation of the hydroxyl group with respect to the aromatic ring. We recorded 25 a- and b-type rotational transitions for p-cyanophenol; the b-type transitions are split by 40 MHz. The rotational constants are A = 5612.96(2) MHz, B = 990.4283(6) MHz, and C = 841.9363(6) MHz. The ground state spitting DeltaE is 20.1608(6) MHz and the barrier to internal rotation, V(2), is 1413(2) cm(-1) from a fit of the rotational transitions to an internal axis system Hamiltonian. The barrier to internal rotation was modeled at the MP2/6-311++G(d,p) level and the effects of substituents on the phenolic ring and the barriers to internal rotation are discussed.

Rapid capture of large amplitude motions in 2,6-difluorophenol: High-resolution fast-passage FT-MW technique

“…5. This value is in a good agreement with previously reported values (phenol [9] 1207(18) cm À1 ; p-fluorophenol [20] 1006(3) cm À1 , p-cyanophenol [21] 1413 (2)) for the proton tunneling in phenols.…”

Internal Rotation of the Acetyl Methyl Group in Methyl Alkyl Ketones: The Microwave Spectrum of Octan‐2‐one

“…0.00 [c] 1.21 [e] 1.76 [c] 0.00 [e] [a] Rotational constants obtained from the XIAM(1Top) fit, see ing rotational constants for assignment purposes in a variety of molecules, as shown in many of our own investigations [20][21][22] and studies in the literature. [23][24][25] Nevertheless, for methyl nalkyl ketones, [2][3][4] especially their C 1 conformers, the accuracy of the rotational constants predicted at this level does not satisfy the experimental requirements which are crucial for a successful assignment of the microwave spectrum (see Section 3). Therefore, geometry optimizations were repeated, applying different combinations of methods and basis sets to find better alternatives.…”

“…Nevertheless, a good agreement between X e and X 0 is often accidentally achieved at the MP2/6-311 + + G(d,p) level due to error compensation. [20][21][22][23][24][25] This does not apply for the C 1 conformers of methyl alkyl ketones. Good starting values for the rotational constants of octan-2-one can instead be determined with a semi-empirical correction using experimental data of other methyl alkyl ketones, like for example heptan-2-one, [4] and the following equation:…”

“…The MP2/6‐311++G(d,p) level of theory has been chosen for the geometry optimizations, since it has provided a good balance between speed of calculation and reliability in predicting rotational constants for assignment purposes in a variety of molecules, as shown in many of our own investigations and studies in the literature . Nevertheless, for methyl n ‐alkyl ketones, especially their C 1 conformers, the accuracy of the rotational constants predicted at this level does not satisfy the experimental requirements which are crucial for a successful assignment of the microwave spectrum (see Section 3).…”

Monitoring of optimized SERS active gel substrates for painting and paper substrates by unilateral NMR profilometry

“…[8] When considering the nowadays constraints of sampling artworks, surface enhanced Raman spectroscopy (SERS), another advanced Raman spectroscopic method has found a successful niche in this field and is fast becoming the technique of choice in cultural heritage laboratories through the continuous correlation and adaption of current methods and techniques from colleagues active across broad fields of Raman and SERS applications. [9,10] Since the turn of the century SERS has found a successful niche in art historical materials as a micro-invasive technique for the examination of historic and archaeological textile fibres, watercolours, pastels, paints and paintings through an array of methods adapted by many active groups from acid hydrolysis to extraction less in-situ measurements involving specifically prepared active substrates. [11][12][13][14] Coupled with specifically compiled in-house searchable databases [15] and the possibility to combine the chosen SERS method with further techniques such as TLC, [16] theoretical calculations [17] and chemometric approaches [18] amongst others render the SERS toolbox increasingly competitive to the more traditional established invasive methods.…”