Which of the following statement is correct for NMR spectrum of isopropyl bromide ?

Q: Which of the following statement is correct for NMR spectrum of isopropyl bromide ?

Which of the following statement is correct for NMR spectrum of isopropyl bromide ?

Question

Accepted Answer

Option 1 is correct: "Absorption by six methyl protons appear up field."

1. **Explanation for Option 1:**
   - In NMR spectroscopy, the chemical shift of protons is influenced by their electronic environment. In isopropyl bromide, the six methyl protons are attached to a carbon that is further away from the electronegative bromine atom compared to the methine proton. This results in the methyl protons experiencing a more shielded environment, causing their absorption to appear upfield (at a lower chemical shift) in the NMR spectrum. This is consistent with the typical behavior of methyl groups in alkyl halides, where they appear upfield relative to protons that are closer to electronegative atoms.

2. **Explanation for why other options are incorrect:**

- **Option 2: "Absorption of lone proton appears up field."**
     - The lone proton in isopropyl bromide is the methine proton, which is directly attached to the carbon bonded to the bromine atom. The electronegative bromine deshields this proton, causing its absorption to appear downfield (at a higher chemical shift) rather than upfield. Therefore, this statement is incorrect.

- **Option 3: "Absorption of lone proton splits into quartet."**
     - The methine proton in isopropyl bromide is coupled with the six equivalent methyl protons. According to the n+1 rule in NMR, where n is the number of neighboring protons, the methine proton would split into a septet (6+1=7) due to the coupling with the six methyl protons. Thus, the statement that it splits into a quartet is incorrect.

- **Option 4: "Absorption of six methyl protons split into quartet."**
     - The six methyl protons are equivalent and are coupled to the single methine proton. According to the n+1 rule, the methyl protons would split into a doublet (1+1=2) due to the coupling with the single methine proton. Therefore, the statement that they split into a quartet is incorrect.

In conclusion, Option 1 is the correct statement as it accurately describes the behavior of the six methyl protons in the NMR spectrum of isopropyl bromide, appearing upfield due to their relatively shielded environment.