NMR Spectroscopy: Quiz

NMR Spectroscopy: Quiz

7 questions

1. Question 1EasyHow many ¹H NMR signals does ethanol, CH₃CH₂OH, give?

   A1B2C3D6
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   Answer: 3

   Three hydrogen environments: CH₃, CH₂ and OH, in a 3 : 2 : 1 ratio.

2. Question 2EasyInto how many peaks is a CH₂ signal split if the neighbouring carbon is a CH₃?

   A2B3C4D5
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   Answer: 4

   n + 1 rule: 3 neighbouring H give 3 + 1 = 4 peaks (a quartet).

3. Question 3EasyA signal at about 9.7 ppm most likely comes from:

   Aan alkyl CH₃Ban aldehyde CHOCan O–CH₃ groupDTMS
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   Answer: an aldehyde CHO

   Aldehyde hydrogens appear at 9–10 ppm. Alkyl H are around 1 ppm, O–CH₃ about 3.3–4.3 ppm, and TMS is 0.

4. Question 4MediumOn a 300 MHz spectrometer, a signal is 360 Hz from TMS. What is δ?

   A0.83 ppmB1.20 ppmC120 ppmD108 ppm
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   Answer: 1.20 ppm

   δ = 360 Hz ÷ 300 MHz = 1.20 ppm.

5. Question 5MediumMethyl ethanoate, CH₃COOCH₃, gives which ¹H NMR spectrum?

   AOne singlet (6H)BTwo singlets (3H each), at about 2.0 and 3.7 ppmCA quartet and a tripletDTwo doublets
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   Answer: Two singlets (3H each), at about 2.0 and 3.7 ppm

   The two CH₃ groups are in different environments (next to C=O and on O). Neither has H on a neighbouring carbon, so both are singlets.

6. Question 6HardWhat splitting does the CH₃ signal of 2-bromopropane, (CH₃)₂CHBr, show?

   ASingletBDoubletCTripletDSeptet
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   Answer: Doublet

   Each CH₃ is next to the CH, which has 1 H: 1 + 1 = 2 peaks. (The CH itself is split by 6 H into a septet.)

7. Question 7HardA compound C₃H₈O shows a doublet (6H) at 1.2 ppm, a septet (1H) at 4.0 ppm and a singlet (1H) at 2.2 ppm. What is it?

   APropan-1-olBPropan-2-olCMethoxyethaneDPropanone
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   Answer: Propan-2-ol

   Two equivalent CH₃ (6H, doublet) next to one CH (septet, on C–O at 4.0 ppm), plus an OH singlet: (CH₃)₂CHOH.