Formation of a dual hydrogen bond in the N-H...C=O moiety in the indole-(N-methylacetamide)1 cluster revealed by IR-dip spectroscopy with natural bond orbital analysis.
IR-dip spectra in the NH stretch regions have been measured for the S(0) state of the indole/N-methylacetamide 1:1 clusters (Ind-NMA(1)). We identified two structural isomers of Ind-NMA(1) that possess an N-H...O=C hydrogen bond. The redshifts of the NH stretch fundamental of the indole moieties in Ind-NMA(1) are larger than that for Ind-(H(2)O)(1) [Carney, Hagemeister, and Zweir, J. Chem. Phys. 108, 3379 (1998)], indicating that the strength of the N-H...O=C hydrogen bond in Ind-NMA(1) is stronger than that of the N-H...O-H hydrogen bond in Ind-(H(2)O)(1). On the basis of the natural bond orbital analysis we suggest that two lone pair orbitals of the O atoms in the NMA moiety form a dual hydrogen bond with the NH group designated by N-H:::O=C. Owing to the dual nature of the N-H:::O=C hydrogen bond its strength in Ind-NMA(1) is larger than that of the N-H...O-H hydrogen bond in Ind-(H(2)O)(1).
Sakota
Kenji
K
Department of Chemistry, Faculty of Sciences, Graduate School of Science, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
Shimazaki
Yuiga
Y
Sekiya
Hiroshi
H
D000081:Acetamides / Q000737:chemistry*; D003198:Computer Simulation; D006860:Hydrogen Bonding; D007211:Indoles / Q000737:chemistry*; D008956:Models, Chemical; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared / Q000379:methods
D000081:Acetamides; D007211:Indoles; C018595:N-methylacetamide