Hydrogen-bonded complexes of phenylacetylene with water, methanol, ammonia, and methylamine. The origin of methyl group-induced hydrogen bond switching.
The infrared spectra in the acetylenic C-H stretching region for the complexes of phenylacetylene with water, methanol, ammonia, and methylamine are indicative of change in the intermolecular structure upon substitution with a methyl group. High-level ab initio calculations at CCSD(T)/aug-cc-pVDZ level indicate that the observed complexes of water and ammonia are energetically the most favored structures, and electrostatics play a dominant role in stabilizing these structures. The ability of the pi electron density of the benzene ring to offer a larger cross-section for the interaction and the increased polarizability of the O-H and N-H groups in methanol and methylamine favor the formation of pi hydrogen-bonded complexes, in which dispersion is the dominant force. Further, the observed phenylacetylene-methylamine complex can be tentatively assigned to a kinetically trapped higher energy structure. The observed methyl group-induced hydrogen bond switching in the phenylacetylene complexes can be attributed to the switching of the dominant interaction from electrostatic to dispersion.
Sedlak
Robert
R
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic and Center for Biomolecules and Complex Molecular Systems, Flemingovo nam. 2, 166 10 Prague 6, Czech Republic.
Hobza
Pavel
P
Patwari
G Naresh
GN
D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry; D000641:Ammonia / Q000737:chemistry*; D006860:Hydrogen Bonding; D000432:Methanol / Q000737:chemistry*; D008744:Methylamines / Q000737:chemistry*; D011789:Quantum Theory; D013696:Temperature; D014867:Water / Q000737:chemistry*
D008744:Methylamines; D014867:Water; C044736:phenylacetylene; D000641:Ammonia; C027451:methylamine; D000114:Acetylene; D000432:Methanol