Spectroscopy 2 Carbon-13 NMR: Nuclear Magnetic Resonance spectroscopy objectives

Question

Spectroscopy 2 Carbon-13 NMR: Nuclear Magnetic Resonance spectroscopy objectives Learn about the energy transitions that give rise to NMR signals. Learn how signals in C-13 NMR spectra relate to chemical structure. Learn how to use Spinworks software to generate in C-13 spectra from raw data, Reference Material The PowerPoint presentation is provided on eCampus Mohrig: p 348-366, 391-417. Much of this material is focused on proton N number will introduced in However, the basic principles that affect the do not of be a few weeks. similar. Integration and spin-spin splitting shift and chemical shifts are quite NMR. Chemical apply with 13 NMR: these will be introduced with proton orrelation charts can be found can be found on pages 413 and 414 Background Resonance (NMR) spectroscopy is the most powerful identification technique available to organic chemists. It detects only elements that have nuclear which means that (IH) and (a c) are in NMR, and this There are other nuclei that are active in NMR, but they will not be considered in Organic Chemistry l or IL We are introducing C-13 NMR first because C-13 interpretation is more traightforward than that for proton NMR, and our 400 MHz spectrometer is capable of recording both types of spectra. C-13 NMR is inherently less sensitive than proton NMR. Most of the carbon in the universe is 2c. which has no spin and therefore does not give NMR signals. Thus for this method we rely on the 1,1% natural abundance of 5C. This requires a very sensitive instrument, which uses the Fourier Transform (FT method of signal acquisition (Mohrig, pp 350-352) so that many scans can be averaged to enhance the signal. A relatively large sample size is also helpful. The low natural abundance of 15C means that it is very unlikely that two "C atoms are situated next to each other, which greatly simplifies 130 spectra but also makes them less informative The key piece of information provided NMR number of different signals, which corres ponds of chemical environments in a molecule 411) chemical environments are determined by the sorts of functional groups they are near or sited The spectrometer measures these differences in chemical environment as chemical to chemical are measured in parts per million (6 values). Fortunately for us values are related in useful ways that help to determine or confirm structures. Note that

Explanation / Answer

(1)

The overall spin of a nucleus makes it observable in the NMR spectroscopy.

(2)

When a nuclues containing inherent spin ( and thus inherent magnetic moment ) is placed in an external field, it absorbs energy and aligns its spin in an anti parallel direction as compared to that of the external field.

(3)

The powerful magnets help create a magentic field which is strong enough to cause the spin shift ( or the energy transition ) in the nucleus.

(4)

If all the NMR signals show up in the same place, this would mean that all the atoms in the molecule are identical, so there would be no way to distinguish between them.

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.