Organic Chemistry Questions and Answers – Nuclear Magnetic Resonance – 1

This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Nuclear Magnetic Resonance – 1”.

1. Which of the following organic compound with molecular formula C₃H C₁₂ exhibits only one signal in the IH NMR spectrum?
a) 2, 2-dichloropropane
b) 1, 2-dichloropropane
c) 1, 3-dichloropropane
d) 1, 1-dichloropropane
View Answer

Answer: a
Explanation: Only (a) compound has all chemically equivalent hydrogen. So, give only one peak.

2. The 1_H NMR spectrum of CH₃OCHCICH₂Cl will exhibit ________
a) A three proton doublet. One proton singlet and a two proton doublet
b) A three proton singlet. One proton singlet and a two proton doublet
c) A three proton singlet. One proton triplet and a two proton doublet
d) A three proton triplet. One proton triplet and a two proton triplet
View Answer

Answer: c
Explanation: The 1H NMR spectrum of CH3OCHCICH2Cl will exhibit three proton singlet, one proton triplet and two proton doublet.
No. of peaks = n + 1
(n = no. of neighbouring chemically equivalent Hydrogen nuclii)

3. Which of the following 1_H-NMR spectrum of compound with molecular formula C₄H₉NO₂ shows delta 5.30 (broad, IH), 4.10(q, 2H), 2.80 (d, 3H), 1.20 (t, 3H) ppm?
a) CH₃NHCOOCH₂CH₃
b) CH₃CH₂NHCOOCH₃
c) CH₃OCH₂CONHCH₃
d) CH₃CH₂OCH₂CONH₂
View Answer

Answer: a
Explanation: C₄H₉NO₂;
chemical shift = 5.30 (broad, 1H)
chemical shift = 4.10 (q, 2H)
chemical shift = 2.80 (d, 3H)
chemical shift = 1.20 (t, 3H)

As shown in the above compound, doublet, because of neighbouring 1H attached to N and one will be broad as because of hydrogen attached to N, quatret becauseof neighbouring 3H and finally triplet, because
of neighbouring 2H.

4. Which of the following has three types of hydrogens in the following compounds?
a) Br-CH = CH₂
b) CH₃ – CH₂ – CH₃
c) C₆H₅CH₂
d) CH₃– CH₂ – CH(CH₃) – N0₂
View Answer

Answer: a
Explanation:

We will replace them by D and check the structure if they are different then they are different.

both are different
so, total 3 type of hydrogen
So, three different type of hydrogen is present in compound a.

5. Which of the compound show only one signal is present in the PMR spectra?
a) C₃H₄, C₃H₆
b) C₄H₆, C₅H₁₂
c) C₈H₁₈, C₂H₆O
d) All of the mentioned
View Answer

Answer: d
Explanation: All of the below compounds have only type of proton, so only one signal.

6. How many Hertz does 1 ppm correspond to for an PMR spectrometer operating at a radio frequency of 60 MHz and 100 MHz?
a) 6 Hz, 10 Hz
b) 60 Hz, 100 Hz
c) 100 Hz, 60 Hz
d) 10Hz, 100Hz
View Answer

Answer: b
Explanation:

7. Compound C₄H₁₀O gave PMR spectrum consisting of two groups of lines (multiplets) with relative intensities in the ratio 3 : 2. Other compound of the same formula exhibited two lines with relative area of 9 : 1. What are these compounds.
a) Diethyl ether and n-butanol
b) t-Butyl alcohol and 1-Methoxypropane
c) diethyl ether and t-Butyl alcohol
d) Diethyl ether and 2-Methoxypropane
View Answer

Answer: c
Explanation: NMR data: Two groups of lines in 3 : 2 and two groups of lines in 9 : 1 for same molecular formula
a) CH₃–CH₂–O–CH₂–CH₃

6Ha -> 1 group of line;
4Hb -> 1 group of line

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Therefore, Intensity => 6 : 4 => 3 : 2.
b)
9H -> 1 group of line and 1H -> 1 group of line / single peak.
Therefore, Intensity => 9 : 1.

8. The distance between the centers of the peaks of doublet is called as?
a) Coupling constant
b) Spin constant
c) Spin-spin coupling
d) Chemical shift
View Answer

Answer: a
Explanation: When the proton under observation is split into several peaks by neighboring protons, the distance between these peaks is a constant called the coupling constant (J). Any two sets of protons that exhibit the same coupling constant are most likely splitting eachother signals and are said to be coupled.

9. H₂, CH₄, C₂H₆ and C₆H₆ exhibit which PMR spectra?
a) Singlet
b) Doublet
c) Triplet
d) Quintet
View Answer

Answer: a
Explanation: All structures have only one type of hydrogen. So, all give single peak.

10. A proton Hb is coupled to four equivalent protons Ha. The multiplicity and the relative intensity of lines in the signal Hb is?
a) Doublet, I : 4
b) Triplet, I : 4 : 6
c) Quintet, 1 : 4 : 6 : 4 : 1
d) Quartet, 1 : 4 : 6 : 4
View Answer

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