A theoretical NMR study of ortho and para-substituted benzenes compared with silabenzenes, pyridines and phosphabenzenes

Abstract

The experimental spin-spin coupling constants (SSCCs) for 1,3- and 1,4-difluorobenzene have been determined anew, and found to be consistent with previously determined values. SSCCs for 1,2-, 1,3-, and 1,4-difluorobenzene have been analyzed by comparing them with the coupling constants computed using the second-order polarization propagator approximation (SOPPA) and the equation-of-motion coupled cluster singles and doubles method (EOM-CCSD). Eighty experimental values have been analyzed using SOPPA calculations, and a subset of 40 values using both SOPPA and EOM-CCSD approaches. One-bond coupling constants (1)J(C-C) and (1)J(C-F) are better described by EOM-CCSD, whereas one-bond (1)J(C-H) values are better described by SOPPA. An empirical equation is presented which allows for the prediction of unknown coupling constants from computed SOPPA values. A similar approach may prove useful for predicting coupling constants in larger systems.

The structure of azines derived from C‐formyl‐1H‐imidazoles in solution and in the solid state: tautomerism, configurational and conformational studies

“…The following equations have been used to transform absolute shieldings into chemical shifts: δ 1 H = 31.0 – 0.97* σ 1 H, (reference TMS, 0.00 ppm) δ 13 C = 175.7 – 0.963* σ 13 C, (reference TMS, 0.00 ppm) δ 15 N = –152.0 – 0.946* σ 15 N , (reference ext. neat MeNO 2 , 0.00 ppm)…”

“…All the calculations have been carried out with the Gaussian-09 package. [26] The following equations have been used to transform absolute shieldings into chemical shifts: d 1 H = 31.0-0.97*s 1 H, (reference TMS, 0.00 ppm) [27] d 13 C = 175.7-0.963*s 13 C, (reference TMS, 0.00 ppm) [28] 0.00 ppm) [28] Solvent effects have been calculated within the PCM approximation. [29][30][31] Because no solvent model is available for hexamethylphosphoramide (HMPA) (the main solvent used experimentally), we have followed the advice of Wangg et al [32] and carried out our PCM calculations in methanol because it has a dielectric constant (eMeOH = 32.6) very similar to that of HMPA (eHMPA = 30).…”

2‐(Dimethylamino)phosphinin: Ein phosphorhaltiges Anilinderivat

“… [7] Phosphinin 1 repräsentiert das erste phosphorhaltige N , N ‐Dimethylanilin‐Derivat und zeigt eine einzelne Resonanz bei δ =126.5 ppm im 31 P{ 1 H}‐NMR‐Spektrum. Dieser Wert ist im Einklang mit der von Alkorta und Elguero berechneten 31 P‐NMR‐Verschiebung von 2‐Phosphaanilin (2‐H 2 N‐C 5 H 4 P, δ =130.0 ppm [25] ) und zeigt erneut die signifikante Wechselwirkung der stark π‐donierenden (CH 3 ) 2 N‐Gruppe mit dem π‐System des P‐Heterozyklus. Im Gegensatz dazu besitzt die Stammverbindung C 5 H 5 P eine chemische Verschiebung bei δ =206.6 ppm im 31 P{ 1 H}‐NMR‐Spektrum [7] …”

Theoretical NMR Study of the Hydrogen Bond and CH-π Interactions in FH Pyridine ┴ X-Benzene Complexes

“…They compared their results with silabenzenes, pyridines and phosphabenzenes. [23] Other authors investigated also the NMR properties of ternary complexes involving hydrogen bonds. [24] Cooperativity of the hydrogen bond and CH-π interactions has been previously reported and it was shown that there is a positive cooperativity between hydrogen bond and CH-π interactions in the modeled complexes formed from HF, pyridine and substituted-benzenes.…”