Predicting ¹³C NMR Spectra by DFT Calculations

Abstract

C chemical shifts and n J CH coupling constants have been determined both experimentally (by means of J-resolved NMR spectroscopy) and theoretically (by DFT calculations) for a series of organic molecules. With the exception of halogen-bonded carbon nuclei, a good correlation is observed between experimental and calculated data. The magnitude of the most important contributions to the spin-spin coupling constant (Fermi-contact, diamagnetic, and paramagnetic spin-orbit contributions) has been determined. The spinorbit terms are negligible or cancel out ( 1 J CH and 3 J CH ), thus leaving the contact term as the only relevant contribution, but become important for 2 J CH in aromatic (but not in aliphatic) compounds. Relativistic effects on the 13 C chemical shift of carbon bonded to a fairly heavy atom (bromine) have also been investigated. Finally, conformational effects on the long-range n J CH coupling constants has been investigated in a model alkane derivative (n-butyl chloride). The implications to structure prediction and determination by NMR are discussed.

FT-IR, NMR spectroscopic and quantum mechanical investigations of two ferrocene derivatives

“…For the NMR calculations, molecular structures of optimized at B3LYP/6-31G(d) level in chloroform ( After optimization, 1 H and 13 GIAO method [23][24][25][26][27][28][29][30] in chloroform at the B3LYP/6 Relative chemical shifts were then estimated by using the corresponding TMS shieldings calculated in advance at the same theoretical levels isotropic chemical shieldings for TMS at the B3LYP/6 using the IEFPCM were 31.87 ppm and 183.76 ppm, respectively. Experimental chemical shieldings for TMS are given as pectroscopic and quantum mechanical investigations of two ferrocene derivatives Bull.…”

“…The standard 1D and 2D hetero and homonuclear NMR experiments are enough to afford complete assignment of compounds and very useful to clarify molecular structures [20][21][22]. For the theoretical NMR investigations, the gauge including atomic orbitals/density functional theory (GIAO/DFT) approach is widely used for various types of compounds [23][24][25][26][27][28][29][30][31]. The DFT/B3LYP method exhibits good performance on electron affinities, excellent performance on bond energies and reasonably good performance on vibrational frequencies and geometries of inorganic or ionic compounds [32,33] as well as organic and neutral compounds [34][35][36][37][38][39][40].…”

“…After the optimization, in order to confirm the convergence to minima on the potential energies, harmonic vibrational frequencies of the present compounds were determined using analytic second derivatives with the ) and 0.967 (under 1800 absence of imaginary frequencies confirmed that the optimized PED calculations were carried out by vibrational 3pica were first fully = 4.9) using the IEFPCM method [27][28][29][30].…”

The isotropic nuclear magnetic shielding constants of acetone in supercritical water: A sequential Monte Carlo/quantum mechanics study including solute polarization

“…Finally, we verify that all values reported here are statistically converged. For the QM calculation of the shielding constants, we use density functional theory ͑DFT͒ that offers a good compromise 25,50 between computational cost and accuracy for molecular properties in condensed phase.…”

Non‐empirical calculations of NMR indirect carbon–carbon coupling constants. Part 8—Monocycloalkanes

“…It is noteworthy that our present SOPPA and SOPPA(CCSD) calculations unambiguously confirmed the signs of 2 J C,C , 4 J C,H a and 4 J C,H e , which were assumed to be negative in the original experimental studies. 91,93 Recently, Bagno et al 96 performed DFT calculations of the eight possible J(C,H) in the frozen cyclohexane taking into account only three terms (Fermi contact, diamagnetic and paramagnetic spin-orbit contributions). Geminal, vicinal and four-bond couplings were well reproduced by those calculations whereas one-bond J(C,H) were considerably underestimated (by ca 9-13 Hz) owing to the too small Fermi contact contributions.…”