Quantification of the Push−Pull Effect in Substituted Alkynes. Evaluation of ±I/±MSubstituent Effects in Terms of C≡C Bond Length Variation

Abstract

(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.

The 13C chemical shift and the anisotropy effect of the carbene electron‐deficient centre: Simple means to characterize the electron distribution of carbenes

“…Because of the +M effect of the NR 2 substituent(s) at the ylide carbon atom of the corresponding N,C, bond(s) get(s) substantial partial C,N double bond character, measurable by dynamic NMR spectroscopy . We have useful experiences with the corresponding orbital occupations from examining the push–pull effect of substituted olefins and acetylenes as well: +M substituents donate π‐electron density into π*, the anti‐bonding orbital of the π bond, and −M substituents attract π‐electron density out of the π bonding orbital; the quotient quantifies the present push–pull character and proved to be quantitatively dependent on the 13 C chemical shift difference of the olefin carbon atoms (Δδ( 13 C)/ppm) . So, because in the carbene case only the push effect of the NR 2 substituent(s) is asked, we have correlated the occupation number of the π* orbital of the partial C,N double bond with the corresponding 13 C chemical shifts of the ylide carbon atom; the correlation is excellent and is given in Figure .…”

Hydroalumination versus Deprotonation of Alkynes with Sterically Demanding Substituents

“…In terminal fragments, monomeric compounds (c. f. compound 4 and ref. [17 -19]) or terminal alkynes [24,25] the difference is usually much smaller. The characteristic shifts δ ( 1 H) of the bridging hydride anions in compounds 2 and 3 are found between δ = 3 and 4.…”

A two-step MM and QM/MM approach to model AIEE of aryloxy benzothiadiazole derivatives for optoelectronic applications

“…Kleinpeter and his coworkers have quantified the push-pull effect in double bonds in organic compounds and have reported a linear dependence of the occupation numbers on the bond lengths. [49][50][51] Therefore, the push-pull effect in HB, FB, CB, NB, and CAB has been studied and is depicted in Fig. 5 for C9-C10, C10-C13, and C12-C13 bonds.…”