Influences of polarizability effect of alkyl group and homoring competition effect of substituents on the NMR spectra of salen‐type Schiff base

Abstract

Salen-type Schiff bases are a kind of important compounds and are widely used. In order to explore the effect of alkyl groups and substituents attached to aromatic ring on the chemical shifts, 63 title compounds were synthesized.Their 1 H NMR and 13 C NMR spectra were obtained; and the effects of the alkyl chain length and substituents on the chemical shifts (δ H (CH N), δ C (CH N), δ H (OH), and δ C (C OH)) were studied. The results show that (1) the alkyl polarizability effect index (PEI) has an important influence on the chemical shifts of the above four atoms, with the increase of PEI, the values of δ H (CH N) and δc(CH N) decrease, and the values of δ H (OH) and δ C (C OH) increase. (2) The influence of substituent X attached to aromatic ring on the chemical shift is related to its position by taking OH or CH N as reference. As for the effect of substituent on the chemical shifts, the effect of Hammett constant σ(X) OH and excited-state substituent parameter σ ex CC X ð Þ OH with OH as reference are different from that ofσ(X) CH N and σ ex CC X ð Þ CH N with CH N as reference, and there is a "homoring competition effect" of the substituent.(3) The effect of the cross-interaction between X and OH on the chemical shift is also significantly different due to the different position of X. Quantitative correlation equations against chemical shifts were built for the four atoms, and the stability and prediction ability of the obtained equations were confirmed by leave-one-out cross validation.

Modified NPOH Equation Showing Terminal Effect: Boiling point of homologs monosubstituted alkanes (RX)

“…In order to investigate the contribution of parameters used in Equation (12) to the boiling points, we, according to Equations ( 13) and ( 14), [18][19][20][21] calculated the parameter contributions. The ψ r and ψ f indicate the relative and fractional contributions of the parameter to Equation (12), respectively.…”

Influences of polarizability effect of alkyl group and homoring competition effect of substituents on the fluorescence emission spectra of salen‐type Schiff bases

“…The 63 samples of compounds as synthesized for the previous study [27] were used without purification. Taking anhydrous ethanol as the solvent, the target compounds were dissolved with a concentration of about 10 À3 mol/L, and all solutions were analyzed while fresh.…”

“…Recently, a quantitative study [27] has conducted focusing on the nuclear magnetic resonance (NMR) chemical shifts of 63 salen-type Schiff bases, in which the electronic effects of substituents and changes to alkyl chain length were analyzed. It was found that there is a "homoring competition effect" of the substituent on 1 HNMR and 13 CNMR and point out that the homoring competition effect occurs in conjugated organic molecules with multiple substituents in the same aromatic ring.…”

“…How the substituents' electronic effects and the change in diamine chain length change of the diamine affect the FL em of salen-type Schiff base, though, whether or not the homoring competition effect of the substituents exist in the FL em are issues that lack clarity and are thus worthy of attention. Therefore, in this work, the fluorescence emission spectra of the same 63 compounds, as reported in previous work, [27] were determined when in an ethanol solution, and the effects of the substituent electronic effect and alkyl chain length on the FL em of salen-type Schiff bases were investigated.…”