A, short C-H center dot center dot center dot N hydrogen bond with a very strong IR spectroscopic effect

The crystal structure of 3-methylthio-4-propargylselenoquinoline contains a very short C=C-H . . .N hydrogen bond with H . . .N and C . . .N distances of 2.17 and 3.225(4) Angstrom, respectively. The bathochromic shift of the infrared acetylenic. C-H stretching vibration v(CH) is 176 cm(-1). The geo metry as well as the spectral effects come close to the shortest well-studi ed C-H . . .N hydrogen bond, which occurs in solid HCN (C . . .N = 3.18 Ang strom, bathochromic shift 180 cm(-1)). The hydrogen bond energy is calculat ed as -3.4 kcal mol(-1). A correlation of v(CH), bathochromic shift against C . . .N distance is established for C=C-H . . .N hydrogen bonds.