Steric effects imino compounds

Imino-ethers can adopt theoretically the four conformations 179-182. In addition to the primary electronic effect, conformer 179 possesses two secondary electronic effects, conformers 180 and 181 only one whereas con-former 182 has none. Conformer 179 has a strong steric interaction between the two R groups and must be eliminated. Imino-ethers must therefore exist either in conformation 180 and 181. Meese, Walter, and Berger (40) have shown that the most stable conformation is 180. In some compounds where there is an important steric effect between the R1 and the RN group, conformation 181 is also observed. It was also found that in a polar solvent (CHjOH), there is a mixture of a major (180) and a minor (181) conformer. 

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