Why do carbon and hydrogen atoms resonate at different frequencies?

The different local chemical environments surrounding any particular nuclei causes them to resonate at slightly different frequencies. This is a result of a nucleus being more or less shielded than another. This is called the chemical shift (δ).

Which of the nuclei do not show the nuclear magnetic resonance?

All nuclei with an odd number of protons (1H, 2H, 14N, 19F, 31P …) or nuclei with an odd number of neutrons (i.e. 13C) show the magnetic properties required for NMR. Only nuclei with even number of both protons and neutrons (12C and 16O) do not have the required magnetic properties.

When both mass number and atomic number are even then the spin quantum number is?

If the number of neutrons and the number of protons are both even, then the nucleus has NO spin. If the number of neutrons plus the number of protons is odd, then the nucleus has a half-integer spin (i.e. 1/2, 3/2, 5/2)

What is the requirement for a nucleus to exhibit the NMR phenomenon?

In order to interact with the magnetic field in the spectrometer, the nucleus must have an intrinsic nuclear magnetic moment and angular momentum. This occurs when an isotope has a nonzero nuclear spin, meaning an odd number of protons and/or neutrons (see Isotope).

Why TMS is used as a reference in NMR spectroscopy?

Tetramethylsilane became the established internal reference compound for 1H NMR because it has a strong, sharp resonance line from its 12 protons, with a chemical shift at low resonance frequency relative to almost all other 1H resonances. Thus, addition of TMS usually does not interfere with other resonances.

Why all nuclei have different resonance frequency at the same magnetic field strength?

The amount of shielding depends on the chemical composition of the molecule. This means that protons in different chemical compounds will be in slightly different field strengths and will therefore resonate at different frequencies.

Why is carbon 12 Not NMR active?

C NMR spectroscopy is much less sensitive to carbon than 1H NMR is to hydrogen since the major isotope of carbon, the 12C isotope, has a spin quantum number of zero and so is not magnetically active and therefore not detectable by NMR.

How many isotopes have even atomic number?

There are 146 stable even–even nuclides, forming ~58\% of the 252 stable nuclides. There are also 21 primordial long-lived even–even nuclides. As a result, many of the 41 even-numbered elements from 2 to 82 have many primordial isotopes. Half of these even-numbered elements have six or more stable isotopes.

Why are elements with even number of protons more abundant?

Elements with an even number of protons (Z) are typically more abundant than those with and odd number. This is because the two most abundant elements, hydrogen and helium, were made at the birth of the universe. Heavier elements were mostly made in stars.

What isotopes are NMR active?

There are three NMR-active isotopes of hydrogen, the spin-1/2 protium (1H), spin-1 deuterium (2H) and spin-1/2 tritium (3H). Whilst 3H is the most sensitive of all NMR active nuclei, it is radioactive (β-emitter), has a very low natural abundance (3 x 10-16\%) and is difficult and expensive to obtain or produce.

Why cdcl3 is used in NMR?

In proton NMR spectroscopy, deuterated solvent (enriched to >99\% deuterium) must be used to avoid recording a large interfering signal or signals from the proton(s) (i.e., hydrogen-1) present in the solvent itself.