1. Purpose

A good line-shape, as well as high resolution and high sensitivity, are the most important features for the performance of an NMR spectrometer (Exps. 3.5–3.10). In the line-shape test, also often called the hump test, the ¹H NMR signal of CHCl₃ is tested with regard to its line-width by measuring not only the width at half height (50%), but also that at the height of the ¹³C satellites (0.55%) and at 1/5 of this height (0.11%). NMR signals should have a Lorentzian line-shape. Therefore the widths at the latter two heights should be 13.5 and 30 times the half-height line-width Δν_1/2 (e.g., for Δν_1/2 = 0.2 Hz these “hump” values are calculated to be 2.7 and 6 Hz). Deviations from these ratios indicate a non-Lorentzian line-shape; such a situation should be avoided, even if the measured values are smaller than the calculated ones.

2. Literature

T. D. W. Claridge, High-Resolution NMR Techniques in Organic Chemistry, Pergamon, Oxford, 1999, 106–107.
V. W. Miner, W. W. Conover, The Shimming of High Resolution NMR Magnets, 1997, http://www.acornnmr.com.
C. Anklin, D. v. Ow, H. Ruegger, Standard Test Procedures for Supercon Systems, Spectrospin AG, Fällanden, 1988.

3. Pulse Scheme and Phase Cycle

Single-pulse proton NMR sequence and phase cycle

4. Acquisition

Time requirement: approx. 1 h, very dependent on the skill of the operator and the state of the system.

Sample: 10% CHCl₃ in [D₆]acetone, degassed and sealed, or the appropriate line-shape sample delivered with your instrument.