A ¹H NMR spectrum shows a triplet at 1.2 ppm integrating for 3H, and a quartet at 3.7 ppm integrating for 2H. Which functional group is most consistent with this pattern?
AMethyl ketone (CH₃CO–)
BEthyl ester (–OCH₂CH₃)
CIsopropyl group (–CH(CH₃)₂)
DVinyl group (–CH=CH₂)
An ethyl ester's –OCH₂CH₃ group produces exactly this pattern: the CH₃ is split into a triplet by the adjacent CH₂ (2+1=3 lines), and the CH₂ is split into a quartet by the adjacent CH₃ (3+1=4 lines). The downfield shift of the CH₂ (~3.7 ppm) reflects deshielding by the adjacent oxygen.
Question 2 True / False
In a ¹H NMR spectrum, a proton with a higher chemical shift (more ppm) is more shielded by surrounding electrons.
TTrue
FFalse
Answer: False
Higher ppm means more deshielded, not more shielded. Electronegative groups or aromatic ring currents pull electron density away from a proton, reducing the local magnetic field it experiences and causing it to resonate at higher frequency (higher ppm). A fully shielded reference proton (TMS) resonates at 0 ppm.
Question 3 Short Answer
A compound shows a single ¹H NMR peak integrating for 6H. What does this tell you about the proton environments in the molecule?
Think about your answer, then reveal below.
Model answer: All six protons are chemically equivalent — they exist in a single magnetic environment and produce one signal. This is consistent with a symmetric structure such as acetone (two equivalent CH₃ groups) or dimethyl ether.
One signal means one distinct chemical environment. The integration of 6H suggests either six equivalent protons (like a single CH₃CH₃ group) or two sets of three equivalent protons that happen to have the same shift — though the latter is much less common. Symmetry in the molecular structure is the usual cause.