⁷⁷Se NMR Spectroscopy As a Sensitive Probe for Hammett σ Constants

Abstract

Herein we showcase the use of a combination of (1)H, (13)C, and (77)Se NMR spectroscopy as a sensitive tool for correlation analysis. A series of substituted O-aryl selenocarbamates [ArOC(Se)N(CH3)2] and Se-aryl selenocarbamates [ArSeC(O)N(CH3)2] have been investigated by means of (1)H, (13)C, and (77)Se NMR spectroscopy. We have determined the (1)H, (13)C, and (77)Se chemical shift values as well as both one- and two-bond heteronuclear (13)C-(77)Se coupling constants, and the changes in both the chemical shift values and the coupling constants were found to obey linear free energy relationships with Hammett's σ(p) and σ(p)(-) constants. For the eight studied O-aryl selenocarbamates, we observe linear free energy correlations with two of the (13)C and (77)Se chemical shift values and as well as one (13)C-(77)Se coupling constant. With the five examples of Se-aryl selenocarbamates, linear correlations are observed with three different (13)C-(77)Se coupling constants. The strong internal consistency validates the use of (77)Se NMR spectroscopy for correlation analysis.

Selenium‐NMR Spectroscopy in Organic Synthesis: From Structural Characterization Toward New Investigations

“…For this reason, the best option is to employ a sealed tube as an external standard. This approach was used by Pittelkow and co‐workers, in 2015, to carry out a relationship between 77 Se−{ 1 H} NMR chemical shift and Hammett σ constants, using an external standard of diphenyl diselenide in CDCl 3 [69] . The correlations between thermodynamic and kinetic parameters are important for elucidating reaction mechanism, and in this work, 13 C− 77 Se NMR coupling constants also demonstrated a linear free energy relationship with the Hammett's σ constants of the substituents.…”

A General Synthesis of Phosphorus‐ and Arsenic‐Containing Analogues of the Thio‐ and Seleno‐cyanate Anions

“…This value corresponds with previously reported 1 J CÀSe coupling constants in which the C À Se bond exhibits double-bond character (226-286 Hz, the latter for SeCO), and differ significantly from values expected for CÀSe single bonds (90-100 Hz). [21] The 77 Se NMR shift of the AsCSe À ion, d = 248.35 ppm, differs greatly from that of PCSe À (d = 84.3 ppm), which we attribute to the greater pacidity of the central carbon atom in AsCSe À relative to PCSe À . [22] Theinfrared spectra of the phosphorus-containing anions PCCh À (Ch = S, Se) reveal bands at 1374 and 1311 cm À1 , respectively,f or their n 1 ("antisymmetric") stretching modes (Table 4).…”

“…[21] The 77 Se NMR shift of the AsCSe À ion, d = 248.35 ppm, differs greatly from that of PCSe À (d = 84.3 ppm), which we attribute to the greater pacidity of the central carbon atom in AsCSe À relative to PCSe À . This value corresponds with previously reported 1 J CÀSe coupling constants in which the C À Se bond exhibits double-bond character (226-286 Hz, the latter for SeCO), and differ significantly from values expected for CÀSe single bonds (90-100 Hz).…”

Stereoelectronic Characterization and Catalytic Potential of a 1,3‐Bis(2,6‐terphenyl)‐Substituted N‐Heterocyclic Carbene

“…Spectra were referenced due to solvent residual signal, excepting 77 Se spectra which were referenced externally to a saturated solution of diphenyl diselenide in CDCl 3 at 25°C (δ Se 463 ppm). [51] Compounds for infrared spectroscopy (4000 to 400 cm À 1 ) were prepared as Nujol mulls or dichloromethane solutions and the spectra recorded on a Nicolet Avatar 320 FTIR spectrophotometer (NaCl windows). Spectra are reported in wavenumbers (cm À 1 ) and the intensity of the absorbances is denoted as strong (s), medium (m) or weak (w…”