Conformational analysis of chlorocholine analogues

The high-resolution proton magnetic resonance spectra of the methylene groups of 2-chloroethyl trimethyl ammonium chloride (I) and 2-chloroethyl dimethyl ammonium chloride (II) were studied by iterative computer calculation. From the values of the spectral parameter L it is concluded that in the case of compound (I) the enthalpy difference between the antiperiplanar and the synclinal conformers is very low, probably, emphasis lies on the antiperiplanar conformation. Compound (II) exists in a dominant synclinal conformation. PCILO calculations of 2-chloroethyl trimethyl ammonium yield the antiperiplanar conformation as the most stable one in agreement with experiment. The energy difference between the antiperiplanar and the syn/anticlinal conformation is 0.7 kcal mole^?1. 2-Chloroethyl dimethyl ammonium, 2-chloroethyl methyl ammonium and 2-chloroethyl ammonium in our PCILO calculations exist in a predominant synclinal conformation. The calculated charge distributions demonstrate that the quaternary nitrogen atom is approximately neutral, the “positive” charge is distributed among the methyl groups and hydrogen atoms attached to the nitrogen atom.