DFT studies of conversion of methyl chloride and three substituted chloromethyl tetrahydrofuran derivatives during reaction with trimethylamine.

B3LYP/6-31+G** level computations were performed for the formation of four trimethylammonium salts in the reaction of methyl chloride ( 1a), ( S)-1,4-andydro-5-chloro-2,3,5-trideoxypentitol ( 2a), (2 S,5 S)-2,5-andydro-6-chloro-1,3,4,6-tetradeoxyhexitol ( 3a) and methyl 5-chloro-2,3,5-trideoxy-β-D-pentofuranoside ( 4a) with trimethylamine. All the structures were fully optimized in the gas phase, in chloroform and water. In addition, B3LYP/6-311++G** and MPW1K/6-31+G** level calculations were carried out to estimate activation barrier heights in the gas phase. A detailed description of all stationary points is presented, and the conformational behavior of the THF ring is discussed. B3LYP and MPW1K activation barriers indicate the reaction between methyl chloride and trimethylamine to be the fastest, whereas reaction 4 is the slowest one, both in the gas phase and in solvents. THF ring conformation changes were observed for reactions 2 and 3 along the reaction pathway, whereas it was almost unchanged for reaction 4, in the gas phase. In the case of reactions 2 and 3, different shapes of the THF ring were found for the transition state geometry in the gas phase and in water. The E→ E and E→ E conformational changes were observed for reactions 2 and 3, respectively. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]