Note, however, that selective excitation isn’t perfect – some of the excitation goes outside the boundary you draw. In the process, you select a narrow range for excitation that corresponds to your peak the mechanics of this step are *just* like integrating. In a 1D NOESY, you’re selecting a single peak of interest to excite, aka “invert”. Step 2: Select the peak(s) you want to excite For best results, open the Topshim GUI, select “solvent suppression” as the shimming method, and in the TUNE section select “Z-X-Y-XZ-YZ-Z” for the “After” method (doing “Before” in also fine). Make sure your shimming is good, as it ensures the base of your excited peak will be narrow, thus improving excitation. A default Proton8 experiment will work fine as long as you can resolve your peaks. Degassing is best practice if you’re doing very careful absolute distance measurements, but most questions can be answered without it. Some texts suggest you should degas your sample to remove O 2, which is paramagnetic and promotes spin relaxation. It’s best to use a good NMR tube for the best shimming bring out the trusty Wilmad 528-PP from the velvet-lined box you keep for your personal special tubes. For reference, this blog post uses data taken on a 10 mg / 1 mL sample of carvone (MW 150). NOE signals are inherently weak (typically ~0.1-1.0% of regular peaks), so make sure you have a reasonable amount of material for answering the question at hand. Rotating Frame NOESY (ROESY) offers an alternative for these systems. Unfortunately, molecules with MW near 600-900 can tumble at rates that give rise to small or even zero NOE no matter how close the H atoms are. NOE intensity varies with molecular weight because size affects the rate of molecular tumbling.Though they look like they interfere, they integrate to zero across the whole peak, and oftentimes do not affect quantitative measurements. These are known as “zero-quantum coherence artifacts”. NOESY spectra often contain artifact peaks in which multiplets have both positive and negative peaks.The NOE is VERY sensitive to distance large NOE values for close protons drop in proportional to 1/r 6 as distance grows: Internuclear distances can be measured quantitatively in Å if calibrated with a 1H- 1H pair of known separation.NOESY with D8 of just 10 msec (very short) yields almost no magnetization transfer, so the integral of the excited peak in this 1D spectrum can be used for quantitative reference when compared to peaks in spectra acquired with the same parameters (but longer D8 values). Magnetization transfer by NOE between spins can be quantified.It is typically set to around 600 msec for small molecules. By convention, this delay is D8 in Bruker pulse sequences. The NOE builds up during a delay in the experiment called the “mixing time”. NOESY experiments always include a kinetic aspect.It is worthwhile to take as many scans as possible to reveal weak NOE peaks. NOE peaks are weak – typically less than 2% of the intensity of the excited peak, often as little as 0.01%.1D NOESY spectra of small molecules are displayed with the large excited peak phased negative and the NOE peaks phased positive.2D NOESY experiments generally run ~2.5 – 12 hours on typical organic samples, but 1D NOESY experiments can yield significant results in about ten minutes.Oftentimes one runs sets of 1D NOESY spectra, selectively exciting several peaks in separate experiments.
2D NOESY can be run without significant user intervention, but 1D NOESY requires manual selection of one peak for excitation.It can even be used to determine forward/backward rates for systems in equilibrium on the 0.1 – 5 second timescale (NOESY is called EXSY when used for this purpose). It’s good for answering qualitative structural questions like “is this H axial or equatorial?” and “which of these geminal vinyl Hs corresponds to which NMR multiplet?” It can also be used for structure determination, including quantitative 1H- 1H distance measurement (if done carefully). Please recall that the 1H- 1H NOESY shows which hydrogen atoms are close together in space (under 4 or 5 Å), regardless of the chemical bonds between them. Where to find QR codes at the spectrometer computer Why NOESY?