Cesium Ion Pair Acidities of some N,N-Dialkylacetamides and Aggregation of Their Cesium Enolates in Tetrahydrofuran.
Cesium ion pair acidities are reported of some N,N-dialkylacetamides at 25 degrees C in tetrahydrofuran. The cesium enolates of alpha-arylacetamides are essentially monomeric at concentrations of about 10(-)(4) M, but small amounts of dimers are present for the enolates of N,N-dimethyl- and N,N-diethyl(4-biphenylyl)acetamide (K(dimer) is approximately 400 M(-)(1)). The cesium enolate of N,N-dimethyldiphenylacetamide forms small amounts of dimers, but the dimerization constant of <100 M(-)(1) is near the limit of detection of our methods. The enolate of N,N-diethylacetamide has an average aggregation number of 3.3, consistent with a mixture of dimers and tetramers. The cesium ion pair pKs of the alpha-arylacetamides are about 25-26, and that of N,N-diethylacetamide is greater than 33.7. The acidity data are in good agreement with measurements that have been reported in the literature for similar systems.
Krom
James A.
JA
College of Chemistry, University of California, Berkeley, California 94720-1460.
Streitwieser
Andrew
A