H H Cl C Cl C H H Hutch Section 13.11
Give the multiplicity of the following signals. A) H
B) H
C) H
12 Kay Saudbex
H H Cl C Cl C H H Hutch Section 13.11
Give the multiplicity of the following signals. A) H
B) H
C) H
12 Kay Saudbex
The Correct Answer and Explanation is:
To answer the question on the multiplicity of signals for hydrogens in the given molecule, let’s first interpret the structure from your text. It seems to be referring to 1,2-dichloropropane (CH₃–CHCl–CH₂Cl) based on the sequence of atoms and placement of Cl and H atoms.
Structure of 1,2-Dichloropropane (CH₃–CHCl–CH₂Cl):
H Cl Cl H
| | | |
H–C–C–C–H → CH₃–CHCl–CH₂Cl
| | | |
H H H H
Label the hydrogens for analysis:
- A) H on the methyl group (CH₃–)
- B) H on the central carbon (–CHCl–)
- C) H on the CH₂Cl group
A) Methyl group protons (CH₃–)
These hydrogens are adjacent to the CHCl carbon, which has 1 hydrogen (H_B).
- Rule: n + 1 where n = number of neighboring nonequivalent protons.
- n = 1 → multiplicity = 2 → doublet
✅ Multiplicity: Doublet
B) Methine proton (–CHCl–)
This hydrogen is adjacent to:
- One CH₃ group (3 hydrogens)
- One CH₂ group (2 hydrogens)
- n = 3 + 2 = 5 → multiplicity = 6 → sextet
✅ Multiplicity: Sextet
C) CH₂Cl protons
These hydrogens are adjacent to the CHCl carbon (1 hydrogen)
- n = 1 → multiplicity = 2 → doublet
✅ Multiplicity: Doublet
Explanation:
In proton nuclear magnetic resonance (¹H NMR) spectroscopy, multiplicity refers to how a hydrogen atom’s signal splits due to neighboring non-equivalent hydrogens, a result of spin-spin coupling. The n + 1 rule determines this: a hydrogen with n equivalent neighbors will show a signal split into n + 1 peaks.
For 1,2-dichloropropane, we examine the molecule’s environment:
- A) Methyl protons (CH₃–): These three equivalent hydrogens are next to a carbon (CHCl) bearing one hydrogen. That single neighboring proton splits the CH₃ signal into a doublet (1 + 1 = 2).
- B) Methine proton (–CHCl–): This proton is between a CH₃ group (3 H) and a CH₂Cl group (2 H). These five neighboring hydrogens split the signal into six peaks, a sextet (5 + 1 = 6).
- C) CH₂Cl protons: These two equivalent protons are adjacent to the CHCl carbon with one proton. Thus, the signal is split into a doublet (1 + 1 = 2).
It’s important to assume that coupling occurs only through three bonds, and that the protons are not magnetically equivalent to the one being observed. Additionally, electronegative atoms like chlorine withdraw electron density but do not split neighboring hydrogen signals significantly, as Cl has no proton for coupling.
Thus, multiplicities are based on direct proton-proton couplings, yielding:
- A) Doublet
- B) Sextet
- C) Doublet
This analysis provides insight into molecular structure and local chemical environments in NMR spectroscopy.
