Which following assertions are true ?
- unanswered 13C NMR is more sensitive than 1H NMR because of the 1.1% natural abundance of 13C nuclei. 13C nuclei have a ½ spin and can be detected in NMR, opposite to more abundant 12C nuclei. 13C NMR requires a different equipment and cannot be done on the same machine as 1H NMR. 13C NMR is not quantitative. 13C NMR experiments are usually carried out with broadband 1H decoupling in order to simplify spectra.
To determine which of the following assertions about 13C NMR are true, we can go through each statement one by one and explain the reasoning behind them:
1. Unanswered 13C NMR is more sensitive than 1H NMR because of the 1.1% natural abundance of 13C nuclei.
The first part of this statement is true. Unanswered 13C NMR is generally more sensitive than 1H NMR due to the low natural abundance of 13C nuclei (about 1.1%) compared to the high natural abundance of 1H nuclei (about 99%). Since there are fewer 13C nuclei available for detection, higher sensitivity is needed to detect their signals.
2. 13C nuclei have a ½ spin and can be detected in NMR, opposite to more abundant 12C nuclei.
The second part of this statement is true. 13C nuclei have a nuclear spin of ½, just like 1H nuclei, which allows them to be detected in NMR. In contrast, the more abundant 12C nuclei are non-spinning (spin-zero) and do not give rise to NMR signals.
3. 13C NMR requires different equipment and cannot be done on the same machine as 1H NMR.
This statement is generally true. While it is technically possible to perform both 13C and 1H NMR experiments on the same NMR machine, in practice, most laboratories have separate instruments dedicated to each type of NMR. This is because the frequency ranges required for 13C NMR are usually different from those used for 1H NMR, so different equipment configurations are often necessary.
4. 13C NMR is not quantitative.
This statement is not universally true. 13C NMR can be quantitative, but there are certain limitations and challenges associated with it. One of the reasons for this is the lower sensitivity of 13C NMR due to the low natural abundance of 13C nuclei. However, with appropriate calibration and careful experimental techniques, quantitative measurements can be obtained.
5. 13C NMR experiments are usually carried out with broadband 1H decoupling in order to simplify spectra.
This statement is true. Broadband 1H decoupling is commonly used in 13C NMR experiments to simplify the spectra. By applying a strong radiofrequency pulse to selectively irradiate the 1H nuclei, their coupling with the 13C nuclei is removed, resulting in simplified spectra that primarily show the chemical shifts of the 13C resonances without any splitting patterns caused by 1H-13C couplings.
Therefore, the true statements about 13C NMR are:
- Unanswered 13C NMR is more sensitive than 1H NMR because of the 1.1% natural abundance of 13C nuclei.
- 13C nuclei have a ½ spin and can be detected in NMR, opposite to more abundant 12C nuclei.
- 13C NMR experiments are usually carried out with broadband 1H decoupling in order to simplify spectra.