The use of inverse detected NMR for the analyses of diesel oil extracts

Proton detection of {dollar}sp{lcub}13{rcub}{dollar}C and {dollar}sp{lcub}15{rcub}{dollar}N NMR frequencies (reverse operation) affords an increase in sensitivity because their signals are detected through a high-{dollar}gamma{dollar} nucleus.; The results presented herein were the first ones attained with the current NMR system (Bruker AM300) operating in reverse configuration. With this NMR system, {dollar}sp1{dollar}H-{dollar}sp{lcub}13{rcub}{dollar}C two-dimensional inverse shift correlation was 3 times more sensitive than direct shift correlation, and {dollar}sp1{dollar}H-{dollar}sp{lcub}15{rcub}{dollar}N inverse shift correlation was 11 times more sensitive than INEPT (Insensitive Nuclei Enhanced by Polarization Transfer).; For the heterocyclic aromatic compounds studied, {dollar}sp1{dollar}H-{dollar}sp{lcub}15{rcub}{dollar}N HMQC experiments were carried out with a detection limit of less than milligram and {dollar}sp1{dollar}H-{dollar}sp{lcub}15{rcub}{dollar}N HMBC experiments were performed with a detection limit of 3 mg for compounds with proton {dollar}alpha{dollar} to the Nitrogen and 25 mg for compounds with CH{dollar}sb3 alpha{dollar} to the Nitrogen.; NMR experiments were carried out in nitrogenous extracts of diesel oil and Light-Cycle-Oil(LCO). The goals were to obtain {dollar}sp1{dollar}H-{dollar}sp{lcub}13{rcub}{dollar}C HMBC and {dollar}sp1{dollar}H-{dollar}sp{lcub}15{rcub}{dollar}N HMQC/HMBC of these extracts, thereby enabling the differentiation of heterocyclic compounds through their {dollar}sp{lcub}13{rcub}{dollar}C and {dollar}sp{lcub}15{rcub}{dollar}N frequencies. The {dollar}sp1{dollar}H-{dollar}sp{lcub}13{rcub}{dollar}C and {dollar}sp1{dollar}H-{dollar}sp{lcub}15{rcub}{dollar}N maps provided a methodology to distinguish extracts of diesel oil from extracts of LCO. {dollar}sp1{dollar}H-{dollar}sp{lcub}15{rcub}{dollar}N HMBC of the basic extract of diesel oil furnished {dollar}sp{lcub}15{rcub}{dollar}N responses in the 300-310 ppm region, where the tri-aromatic bases have their {dollar}sp{lcub}15{rcub}{dollar}N signals.; The 1D {dollar}sp1{dollar}H and {dollar}sp{lcub}13{rcub}{dollar}C NMR spectra provided qualitative and quantitative information of these extracts and their HPLC fractions. In these fractions, {dollar}sp1{dollar}H NMR was used to investigate average molecular structural changes as the complexity of the fractions increased.; Window functions were intensively employed to maximize the sensitivity of the experiments. This intense use led to research on the modification of the TRAF (Transform of Reverse Added FIDs) window functions, conceived by Traficante and coworkers. The changes made in those functions allow their use in FIDs (Free Induction Decay) acquired longer than the optimum measuring time ({dollar}3{lcub}cdot{rcub}Tsb2sp*),{dollar} for which these digital filters were originally designed. With proper choice of the parameter, it was possible to increase S/N ratio and, simultaneously, resolution of the NMR peaks.