Which one of the following statements regarding ^13 C NMR spectroscopy is CORREC

Question

Which one of the following statements regarding ^13 C NMR spectroscopy is CORRECT? (A) The size of a signal in a ^13 C spectrum is proportional to the number of carbons of a given type. (B) In a ^13C NMR spectrum the number of peaks is equal to the number of carbons in a molecule. (C) Typical chemical shifts in a ^13 C spectrum range from 0 ppm to 10 ppm. (D) The carbons in tetramethysilane are used as a reference and are assigned as having a chemical shift of 0 ppm. (E) ^12 C signals can also appear in a ^13 C spectrum. Which of the following statements is CORRECT? In the electron impact ionization mass spectrum of 2-chlorobutane: (A) The molecular ion is negatively charged from collision with an electron. (B) There would be molecular ion peaks at m/z 92 and 94 in a ratio of approximately 1: 1 due to the two isotopes of chlorine present. (C) There would be molecular ion peaks at m/z 92 and 94 in a ratio of approximately 3: 1 due to the two isotopes of chlorine presen

Explanation / Answer

Answer (A 5) : (D)The carbons in Tetramethyl silane are used as a reference and are assigned as having a chemical shift of 0 ppm.

Explanation:

1. The standard used in 13C-NMR experiments to define the 0 ppm point is tetramethylsilane (TMS).

2. In 13C-NMR it is the signal from the four equivalent carbons in TMS that serves as the standard.

Hence, option (D) The carbons in Tetramethyl silane are used as a reference and are assigned as having a chemical shift of 0 ppm, is correct statement.

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