Microwave spectrum, intramolecular hydrogen bonding, conformational properties and quantum chemical calculations for 3,3,3-trifluoropropanol

摘要

The microwave spectrum of 3,3,3-trifluoropropanol (CF3CH2CH2OH) has been investigated in the 7.5-60 GHz spectral region at a temperature of approximately -30 degrees C. Five all-staggered rotameric forms are possible for this compound. Two of these conformers denoted Gg- and Aa were assigned. Gg- is stabilised by a six-membered intramolecular hydrogen bond formed between one of the fluorine atoms and the hydrogen atom of the hydroxyl group. No such interaction is possible in Aa, in which both the O-C-C-C and H-O C-C chains of atoms is in the anti conformation. The internal hydrogen bond is weak, since the Gg rotamer is only 3.5(10) kJ mol(-1) more stable than Aa. The weak intramolecular hydrogen bond is also evident from the gas-phase infrared spectrum of the O-H stretching vibration. The microwave work has been assisted by ab initio computations at the MP2/6-311 + + G** (frozen core) level of theory, as well as density theory calculations at the B3LYP/6-31G* level. The structural parameters predicted in both these computational schemes are similar, Both methods predict that Gg- is several kJ mol(-1) more stable than other rotameric forms, in agreement with the present experimental findings. [References: 35]