Structure Elucidation by NMR in Organic Chemistry

Abstract

Symbols and Abbreviations 1 Short Introduction to Basic Principles and Methods 1.1 Chemical shift 1.2 Spin-spin coupling 1.3 Coupling constants 1.4 Signal multiplicity (multiplets) 1.5 Spectra of first and higher order 1.6 Chemical and magnetic equivalence 1.7 Continuous wave (CW) and Fourier transform (FT) NMR spectra 1.8 Spin decoupling 1.9 Nuclear Overhauser effect 1.10 Relaxation, relaxation times 2 Recognition of Structural Fragments by NMR

Synthesis of novel O-acylated-D-ribono-1,5-lactones and structural assignment supported by conventional NOESY-NMR and x-ray analysis

“…It is also worth noting that the very low values assigned for coupling between H-4 and H-5a/b in D-ribono-1,5-lactones 3-7 ( 3 J 4,5 <1.7 Hz), compared with those for D-ribono-1,4-lactones 1,8-10 ( 3 J 4,5 2.4-4.5 Hz), are probably associated with an adopted gauche conformation in solution with dihedral angles close to 60 o , leading to weak spin-spin interactions as expected by the Karplus-Conroy equation. 9,38 The NOESY experiments performed with selected lactones not only confirmed the results deduced from coupling constant analysis but also revealed other important structural features (Table 4). Besides the anticipated presence of cross-peaks between H-3 and H-4 in the D-ribono-1,5-lactones 4a-c and 7 (H-3 and H-4 are syn), and its absence in D-ribono-1,4-lactones 9 and 10 (H-3 and H-4 are anti), long-range contacts between H-2 and H-5b were also observed for all ribono-1,5-lactones but not for 1,4-lactones.…”

Criterious Preparation and Characterization of Earthworm-composts in View of Animal Waste Recycling: Part II. A Synergistic Utilization of EPR and ¹H NMR Spectroscopies on the Characterization of Humic Acids from Vermicomposts

“…Other weaker signals in the δ 7.1 to 6.2 range, more abundant in the COHA 1 H-NMR spectrum, can be due to the resonance of pyrrolic or indolic type heterocyclic hydrogens, in agreement with the high nitrogen content of the samples 3 . The presence of pyrrolic hydrogens is in agreement with the existence of porphyrin structures, as suggested by the EPR parameters for the Fe 3+ and Cu 2+ 16.0 Hz), these signals can be assigned to the resonance of trans hydrogens of conjugated double bonds of groups like C(=O)R (R = alkyl, ether), present in the pyrrolic structure 36 .…”

Conformational Preference and Spectroscopical Characteristics of the Active Pharmaceutical Ingredient Levetiracetam

“…Indeed, the quantum chemical calculations give a 2 J 22,23 coupling constant of 13.4 Hz, within the range characteristic for such couplings. 88 The nonequivalence of these protons is observed also in the splitting pattern of the H24 peak which is a doublet of doublets, due to the 3 J coupling of this proton with the H22 and H23 protons.…”

“…Indeed, the quantum chemical calculations give a 2 J 22,23 coupling constant of 13.4 Hz, within the range characteristic for such couplings. 88 The nonequivalence of these protons is observed also in the splitting pattern of the H24 peak which is a doublet of doublets, due to the 3 J coupling of this proton with the H22 and H23 protons.The 1D NMR spectrum (see Fig. 6, top side) shows that the peaks corresponding to the H13-14 and H17-18 pairs are triplets due to the vicinal 3 J coupling with the H15-16 protons, whereas the peak of the last pair is a quintet due to the almost equivalent coupling with the 4 protons of the neighbor methylene units.…”