Question

Which of the following statements are TRUE for first-order analyses of NMR spectra (the type of analysis most commonly done).

The spin-multiplicity of the proton NMR absorption of the methylene group in ethanol-OD is 4.

The difference in absorption frequency is equal to or less than 6 J.

Equivalent protons do not split each other.

First-order multiplets are symmetrical, and their chemical shift is given by the position of the first peak in the multiplet.

Carbon-13, an NMR-active nucleus, has a nuclear spin quantum number of 0.

Answer 1

Structure of ethanol - OD is CH3CH2OD

1. In first order NMR , non equivalent proton split each other into 2nI + 1 peaks.. since I for proton = 1/2 . therefore, splitting into n+1 peaks will occur. since methylene group i.e CH2 has 3 non equivalent protons on adjacent carbon  i .e CH3 , hence it will split into (3+1) i.e 4 lines. hence the multiplicity will be 4. hence, this statement is true.
2. The absorption frequency depends (directly proportional to ) strength of magnetic field applied.
3. equivalent protons have same environment and they do not split each other. hence, this statement is true.
4. the difference between first order and non first order NMR is : when the multiplet in the NMR spectrum shows the intensity ratio as per calculated or pascal instensity ratio , then the spectra is known as 1st order spectrum . for 1st order spectrum value of for interacting multiplet will be more than 10. as the value decreases from 10 , the intensity ratio of multiplet gets distorted and the spectrum is known as non-first order spectrum . First order multiplets are symmetrical about the middle point but the chemical shift is not given by the first peak but it is given by the mean ( or the middle point) . hence, this statement is false.
5. C-13 is an NMR active nuclei with spin quantum number = 1/2 . nuclei with spin quantum number 0 are NMR non active. hence, this statement is false.