Question

Which of the following statements are TRUE for first-order analyses of NMR spectra (the type of analysis most commonly done). True False  The peak multiplicity in a proton spectrum is (n+1), where n is the number of adjacent, equivalent hydrogens. True False  The difference in absorption frequency is equal to or less than 6 J. True False  Carbon-13, an NMR-active nucleus, has a nuclear spin quantum number of 0. True False  The spin-multiplicity of the proton NMR absorption of the methyl group in ethanol-OD is 4. True False  First-order multiplets are symmetrical, and their chemical shift is given by the position of the first peak in the multiplet.

Answer 1

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Please find the detailed solution and explanation of your question below.

ANSWER: The true statements are The peak multiplicity in a proton spectrum is (n+1), where n is the number of adjacent, equivalent hydrogens, and First-order multiplets are symmetrical, and their chemical shift is given by the position of the first peak in the multiplet.

Explanation: The first statement is true because the peak multiplicity in a proton spectrum is given by n+1, where n is the number of adjacent, equivalent hydrogens. The actual formula is given by,

2*n*I + 1

where I for hydrogen is = 1/2

on plugging in the values.

2*n*(1/2) +1 = n+1.

The second statement is false because a first-order spectrum has a difference in absorption frequency is greater than or equal to six. Therefore, statement 2 is false.

The third statement is false because Carbon-13, an NMR-active nucleus, has a nuclear spin quantum number of 1/2 and not 0.

The fourth statement is false because the spin-multiplicity of the proton NMR absorption of the methyl group in ethanol-OD is given by

2*n*(1/2) + 1

where n is the no. of adjacent equivalent Hydrogens so n=2.

on plugging in the values,

2*2*(1/2) +1 = 3

The fifth statement is true because the first-order multiplets are symmetrical, and their chemical shift is given by the position of the first peak in the multiplet. A first-order multiplet arises when no two of the spins within an interacting multispin system have a difference in absorption frequency is equal to or greater than 6 J, and it always contains a symmetrical distribution of line positions about the midpoint of the multiplet.

I hope, this answer helps you to better understanding the NMR spectroscopy.

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