Quantification of the push-pull effect in substituted alkynes. Evaluation of +/-I/+/-M substituent effects in terms of C[triple bond]C bond length variation.
(13)C chemical shifts of alkynes, published to date, were computed at the DFT (B3LYP/6-311G*) level of theory and compared with the experimental delta values, and the agreement was employed as a measure of quality for the underlying structures. For the corresponding global minima structures, thus obtained, the occupation quotients of antibonding pi* and bonding pi orbitals (pi*(C[triple bond]C)/pi(C[triple bond]C)) and the bond lengths (d(C[triple bond]C)) of the central C[triple bond]C triple bond were computed and correlated to each other. The linear dependence obtained for the two push-pull parameters d(C[triple bond]C) and pi*(C[triple bond]C)/pi(C[triple bond]C) quantifies changes in the push-pull effect of substituents while deviations from the best line of fit indicate and ascertain quantitatively to what extend the inductive (+/-I) substituent effect changes with respect to the bond length of the C[triple bond]C triple bond.
Kleinpeter
Erich
E
Chemisches Institut, Universität Potsdam, Karl-Liebknecht-Strasse 24-25, D-14476 Potsdam (Golm), Germany. kp@chem.uni-potsdam.de
Frank
Andrea
A
D000480:Alkynes / Q000737:chemistry*; D003198:Computer Simulation; D008956:Models, Chemical
D000480:Alkynes