Matrix isolation infrared and ab initio study of the conformations of 2,2-dimethoxypropane.

Conformations of 2,2-dimethoxypropane (DMP) were studied using matrix isolation infrared spectroscopy. An effusive source maintained at different temperatures (298, 388 and 430 K) was used to deposit DMP in a nitrogen matrix. As a result of these experiments, spectrally resolved infrared features of the ground and first higher energy conformer of DMP have been recorded, for the first time. The experimental studies were supported by ab initio computations performed at B3LYP/6-31++G** level. Computationally, four minima were identified corresponding to conformers with G+/-G-/+, TG+/-, G+/-G+/- and TT structures. The computed frequencies at the B3LYP level were found to compare well with the experimental matrix isolation frequencies, leading to a definitive assignment of the infrared features of DMP, for the G+/-G-/+ and TG+/- conformers. At the B3LYP/6-31++G** level, the energy difference between the G+/-G-/+ and TG+/- conformers was computed to be 3.25 kcal x mol(-1). The barrier for conformation interconversion, TG+/--->G+/-G-/+, was calculated to be 1.29 kcal x mol(-1). The magnitude of this barrier is consistent with the experimental observation that the spectral features due to the TG+/- decreased considerably in intensity when the matrix was annealed.