title: The study of secondary effects in vibrational and hydrogen bonding properties of 2- and 3-ethynylpyridine and ethynylbenzene by IR spectroscopy.
abstract: Weak hydrogen bonds formed by 2- and 3-ethynylpyridine and ethynylbenzene with trimethylphosphate and phenol were characterized by IR spectroscopy and DFT calculations (B3LYP/6-311++G(d, p)). The structure and stability of ethynylpyridines and ethynylbenzene in the gas phase and in the complexes with trimethylphosphate and phenol are discussed in terms of geometry and electronic charge redistribution. Anharmonic effects are taken into account when calculating vibrational wavenumbers of these systems what lead to partial improvement of agreement with experiment. The changes in the electronic charge distribution are behind the frequency shifts of the CC stretching in opposite direction depending on the role the ethyne molecule has in a hydrogen bonded complex (Δν̃=+9 cm(-1) in trimethylphosphate complexes, Δν̃=-3 cm(-1) in phenol complexes). The association constants were determined by keeping the concentrations of proton donors approximately constant and low enough to avoid self-association and the proton acceptors were present in excess. The values obtained for the association constants and enthalpy changes in C2Cl4 (for trimethylphosphate complexes K≈0.5-1.0 mol(-1)dm(3) and -ΔrH≈6-8 kJ mol(-1), for phenol complexes K≈20-40 mol(-1) dm3-ΔrH≈17-22 kJ mol(-1)) are in good agreement with literature data.
authors.affiliation: Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička c. 54, 10001 Zagreb, Croatia.
authors.forename: Danijela
authors.initials: D
authors.lastname: Vojta
authors.affiliation: Theoretical Division, Los Alamos National Laboratory, NM 87545, USA.
authors.forename: Ivana
authors.initials: I
authors.lastname: Matanović
authors.affiliation: Division of Materials Physics, Ruđer Bošković Institute, Bijenička c. 54, 10001 Zagreb, Croatia.
authors.forename: Goran
authors.initials: G
authors.lastname: Kovačević
authors.affiliation: Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička c. 54, 10001 Zagreb, Croatia. Electronic address: goran.baranovic@irb.hr.
authors.forename: Goran
authors.initials: G
authors.lastname: Baranović
mesh_terms: D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry; D019281:Dimerization; D006860:Hydrogen Bonding; D007700:Kinetics; D011725:Pyridines / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013696:Temperature; D014732:Vibration
chemical_list: D011725:Pyridines; C507758:ethynylpyridine; C044736:phenylacetylene; D000114:Acetylene
keywords: Anharmonic wavenumbers; Ethynylbenzene; Ethynylpyridine; Hydrogen bonding; IR wavenumber shifts