Experimental studies of the 13C NMR of iodoalkynes in Lewis-basic solvents.
The (13)C NMR spectra of two different iodoalkynes, 1-iodo-1-hexyne (1) and diiodoethyne (2), exhibit a strong solvent dependence. Comparisons of the data with several common empirical models, including Gutmann's Donor numbers, Reichardt's E(N)(T), and Taft and Kamlet's beta and pi, demonstrate that this solvent effect arises from a specific acid-base interaction. Solvent basicity measures such as Donor numbers and beta values correlate well with the alpha-carbon chemical shift of 1, but polarity measures such as E(N)(T) and pi do not correlate. The similarity of the solvent effect for 1 and 2 suggests that carbon-carbon bond polarization may not play a role in the change in chemical shift, as previously hypothesized.
Webb
Jeffrey A
JA
Department of Chemistry, State University of New York, Stony Brook, New York 11794-3400, USA.
Klijn
Jaap E
JE
Hill
Philip Aru
PA
Bennett
Jordan L
JL
Goroff
Nancy S
NS