Exit to H3 Spectroscopic Techniques (9813)

Structured Practice: Proton NMR Spectroscopy (H3)

Marked whole-spectrum questions: convert line positions to δ and J, count protons from integrals, choose between candidate structures on the evidence that separates them, and explain D₂O exchange and hydrogen-bond shifts.

GCE A-Level H3 Chemistry 9813-2027

You can take this as many times as you like.

Practise

Answer the questions in any order. Check each answer when you're ready to see the mark scheme. It's for practice only and doesn't count towards mastery.

Recent attempts

History is stored only in this browser.

No completed attempts are saved yet.

This check needs JavaScript to record answers. The reviewed questions are listed below for study.

Choosing between two ester candidates. Ester Y, C$_4$H$_8$O$_2$, is either A, ethyl ethanoate, CH$_3$COOCH$_2$CH$_3$, or B, methyl propanoate, CH$_3$CH$_2$COOCH$_3$. Its $^1$H NMR spectrum was recorded at 400 MHz in CDCl$_3$ with TMS as the reference. The table lists each signal's multiplicity, integral trace height and, for the multiplets, the line positions measured from TMS.

¹H NMR signals of ester Y at 400 MHz in CDCl₃
Signal	Multiplicity	Integral trace height / mm	Line positions from TMS / Hz
P	quartet	18.4	1660.8, 1653.7, 1646.6, 1639.5
Q	singlet	27.5	816.0
R	triplet	27.7	511.5, 504.4, 497.3

Part a: Calculate the chemical shift, δ, of signal P. Give two decimal places. (1 mark): δ in ppm needs no unit, but you may type ppm.
Part b: Give the coupling constant, J, within signal P. (1 mark): Give the value in Hz.
Part c: How many protons does signal P represent? (1 mark)
Part d: Which candidate is Y? (1 mark)
Part e: Which observation rules out the other candidate? (1 mark)
Part f: How far from TMS, in Hz, would signal Q appear on a 60 MHz spectrometer? (1 mark): Give the value in Hz.

Assigning a spectrum with a labile proton. Compound Z, C$_3$H$_8$O, gives the $^1$H NMR spectrum summarised below, recorded in CDCl$_3$. After the sample is shaken with a drop of D$_2$O, signal T disappears and signals S and U are unchanged.

¹H NMR signals of compound Z in CDCl₃
Signal	δ / ppm	Multiplicity	Relative peak area
S	4.01	septet	0.52
T	2.1	broad singlet	0.49
U	1.21	doublet	3.05

Part a: How many protons does signal U represent? (1 mark)
Part b: A student says the septet at δ 4.01 means that proton has seven neighbouring protons. How many equivalent neighbouring protons does it actually have? (1 mark)
Part c: Which structure is Z? (1 mark)
Part d: Which proton gives signal T? (1 mark)
Part e: In a more concentrated solution, signal T moves to a higher δ while S and U stay put. Which explanation fits? (1 mark)

Structured Practice: Proton NMR Spectroscopy (H3)

Practice complete

Your answers