HSQC NMR: What It Is and How to Read It

Short answer

HSQC (Heteronuclear Single Quantum Coherence) is a two-dimensional NMR experiment that correlates the chemical shift of each hydrogen with the chemical shift of the carbon (or other heteroatom, often nitrogen) it is directly bonded to. Each cross-peak in the spectrum is one (1H, 13C) pair, so it tells you which proton sits on which carbon.

What HSQC is

The NYU Chemistry Shared Instrumentation Facility describes its standard experiment as “Heteronuclear Single Quantum Coherence Spectroscopy with gradient selection and INEPT enhancements” and says it “correlates chemical shifts of 1H nuclei directly bonded to 13C sites” (read 2026-11-08). The LibreTexts organic-spectroscopy text gives the same scope: HSQC determines “proton to carbon or heteroatom (often nitrogen) single bond correlations,” and its cross-peaks “show which proton is attached to which carbon or heteroatom” (read 2026-11-08).

In the plot, the proton shifts run along one axis (F2) and the carbon shifts along the other (F1). A cross-peak at, for example, (3.9 ppm, 66 ppm) means a hydrogen resonating at 3.9 ppm is bonded to a carbon resonating at 66 ppm, the worked example used by LibreTexts.

How it works in practice

The sequence starts from 1H magnetization, transfers it to the bonded 13C through the one-bond coupling (the INEPT step), lets the 13C chemical shift evolve during the indirect dimension, then transfers the magnetization back to 1H for detection. A University of Kentucky Chemistry handout on gradient HSQC set-up (read 2026-11-08) makes several practical points that explain why the experiment behaves as it does:

• Transfer delay. The delay is 1/(4J), where J is the one-bond H-C coupling. The handout uses 146 Hz for aliphatic CH and 170 Hz for aromatic CH, and notes that the delay can be tuned for the type of CH you care about.
• Only protons on 13C are seen. Because the sequence selects 1H bound to 13C, which is only about 1.1% of carbons, the spectrometer gain is set much higher than for an ordinary 1H spectrum, and 12C-attached protons are actively suppressed.
• Multiplicity editing. With the “XH/XH3 up, XH2 down” option, CH and CH3 carbons give positive peaks and CH2 carbons give negative peaks. The handout points out that this separates geminal protons with near-identical shifts that overlap in COSY or TOCSY.

The NYU facility page gives one concrete example of default settings for its edited HSQC (pulse program hsqcetgp): 1H width 13 ppm centred at 6.18 ppm, 13C width 165 ppm centred at 75.0 ppm, 1024 points in F2 by 256 increments in F1, and 1JCH set to 145 Hz. These are that facility’s defaults for a general-purpose run, not universal values; widths should follow your own 1H and 13C spectra. Processing there uses a 2D Fourier transform (xfb), manual phasing in both dimensions, baseline correction in each, and optional linear prediction in F1. For processing in desktop NMR software, see the CASRAI MestReNova guide.

Reading an HSQC spectrum: a checklist

1. Pick a cross-peak and read off its proton shift (F2) and carbon shift (F1). That pair is one directly bonded C-H.
2. If the experiment is multiplicity-edited, check the sign or colour of the peak to separate CH/CH3 from CH2.
3. Two cross-peaks at the same carbon shift but different proton shifts indicate a CH2 whose protons are inequivalent.
4. A carbon visible in the 13C spectrum that has no cross-peak has no attached hydrogens (LibreTexts uses the 171 ppm carbonyl of propyl acetate as its example). It must be placed with a long-range experiment such as HMBC.

HSQC compared with related experiments

Experiment	What it correlates	Source statement
HSQC	1H with directly bonded 13C (or heteroatom, often nitrogen)	LibreTexts: single-bond correlations; “more sensitive” than DEPT for the same 13C-1H information
HMBC	1H with 13C two, three and sometimes four bonds away	LibreTexts: “two, three, and even four (if through a conjugated system) bonds”; one-bond correlations are suppressed, so it complements HSQC
DEPT	13C-detected carbon information	LibreTexts: may give the same 13C-to-1H information as HSQC, with lower sensitivity
NOESY	Through-space proximity of protons	See the CASRAI NOESY guide

LibreTexts also notes that HSQC is “also known as” HMQC. Treat HMQC as a related one-bond heteronuclear experiment and check which one a facility’s method actually runs.

Where it matters for labs

HSQC anchors each proton to its carbon, which is why it is read before long-range data are interpreted. The LibreTexts text notes the experiment is not limited to carbon and also covers heteroatoms such as nitrogen. For lab managers, the practical points are method definition and record keeping: write the parameters (spectral widths, 1JCH, increments, editing mode) into the standard operating procedure and the electronic lab notebook entry so the run can be repeated.

Common misunderstandings

• “HSQC shows every carbon.” It shows only carbons that carry at least one hydrogen.
• “HSQC and HMBC give the same information.” HSQC reports one-bond pairs; HMBC suppresses them and reports longer-range links.
• “Default parameters fit any sample.” The values above are one facility’s defaults; the delay depends on the 1JCH value you target (about 146 Hz aliphatic versus 170 Hz aromatic in the Kentucky handout).

FAQ

What is HSQC?

A 2D NMR experiment, Heteronuclear Single Quantum Coherence, that correlates each proton’s chemical shift with the shift of the carbon or heteroatom it is directly bonded to.

How is HSQC different from HMBC?

HSQC shows one-bond C-H pairs; HMBC shows correlations across two to four bonds and suppresses the one-bond signals, so the two are read together.

Why does a carbon have no HSQC peak?

Because it has no attached hydrogens, as with a carbonyl or other quaternary carbon.

Sources

• NYU Chemistry Shared Instrumentation Facility, HSQC-ed experiment guide: wp.nyu.edu/chem_sif/docs/nmr-experiment-guide/2d-experiments/hsqc-ed (read 2026-11-08).
• LibreTexts, Introduction to Organic Spectroscopy, 7.4 Two-Dimensional Heteronuclear NMR Spectroscopy: chem.libretexts.org (read 2026-11-08).
• University of Kentucky Chemistry, 1H-13C HSQC set-up handout: chem.as.uky.edu (read 2026-11-08).