H3 Chemistry 9813 · Study focus: H3 Chemistry: Determine proton equivalence and signal count
H3 Chemistry: Determine proton equivalence and signal count
Start from the governing chemical model, test it against evidence, then transfer the reasoning to an unfamiliar case.
Your success criteria
- Determine proton equivalence and signal count
- Use named chemical evidence.
- Transfer the governing reason to an unfamiliar case.
Count environments, not atoms
Ethane's six protons are equivalent by symmetry and rapid rotation, so they give one 1H environment.
CH3CH2Cl has two environments: CH3 and CH2, despite five proton nuclei.
Chemical equivalence
Equivalent protons have the same chemical environment and chemical shift at the stated treatment.
A symmetry operation or rapid motion can interchange equivalent protons; merely sharing a carbon is not a universal proof.
Replace one candidate proton with a label and compare the resulting structures; symmetry-related replacements support equivalence at this level.
In propane the two terminal CH3 groups are equivalent, while the central CH2 is distinct: two signals with 6H and 2H integrals.
Text alternative: Text lists every labelled set, atom location, proton count and the symmetry operation used.
Use substitution and symmetry tests
Replace one candidate proton with a label and compare the resulting structures; symmetry-related replacements support equivalence at this level.
In propane the two terminal CH3 groups are equivalent, while the central CH2 is distinct: two signals with 6H and 2H integrals.
Count propanone signals
The two CH3 groups in CH3COCH3 are interchanged by symmetry.
All six protons form one environment, so propanone gives one 6H singlet in this simple treatment.
- Predict the number and integral of propanone's proton signals.
Open the feedback checkpoint after attempting
- One signal integrating to 6H; both methyl groups are equivalent by symmetry.
Count ethyl ethanoate
CH3CO2CH2CH3 contains an acyl CH3, OCH2 and terminal CH3.
These are three non-equivalent environments with integrals 3:2:3.
- List the three environments without using multiplicity.
Open the feedback checkpoint after attempting
- Credit COCH3, OCH2 and terminal CH3 as distinct.
Transfer to para-disubstituted benzene
A supplied para-disubstituted ring with identical substituents has symmetry-related proton pairs.
State the symmetry assumption and count sets rather than six individual H atoms.
- Mark equivalent proton pairs in para-dichlorobenzene.
Open the feedback checkpoint after attempting
- Credit two aromatic proton environments, each integrating to 2H.
One proton does not mean one signal
A signal belongs to an environment shared by equivalent protons.
Conversely, protons on one carbon may become non-equivalent in a chiral/asymmetric context, though use only supplied stereochemical information.
- Repair: “C4H10 has ten proton signals.”
Open the feedback checkpoint after attempting
- Count symmetry-related environments for the specified isomer rather than atoms.
Count before interpreting area
Complete twelve fixed equivalence checks, then unseen methyl tert-butyl ether and different disubstituted-benzene re-test.
Next objective: use integration at /learning/h3-nmr-integration-lesson.html.
- Construct an environment table for ethyl ethanoate.
Open the feedback checkpoint after attempting
- Credit three unique environments, 3:2:3 proton counts and explicit structural locations.