HSQC
Heteronuclear Single-Quantum Coherence · Also known as: HSQC NMR, 1H-13C HSQC, heteronuclear correlation
Heteronuclear Single-Quantum Coherence (HSQC) is a 2D NMR technique that correlates proton and carbon-13 (or other heteronuclei) chemical shifts through one-bond coupling constants (1JHX). Developed in the early 1980s, HSQC rapidly became the workhorse of structural chemistry because it directly maps which carbons bear which protons, providing a comprehensive view of carbon skeleton connectivity and substitution patterns.
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When to use it
Apply HSQC to any structure elucidation problem where you need to know which carbons have attached protons. It is particularly powerful for distinguishing CH, CH2, and CH3 groups and for identifying quaternary carbons. HSQC works for any organic or biological molecule; it is especially valuable for large proteins where spectral crowding makes 1D carbon NMR ambiguous. Assumes 13C natural abundance (1.1%) is sufficient for detection, or the sample is 13C-enriched.
Strengths & limitations
- Unambiguously identifies which carbons have attached protons and distinguishes CH, CH2, and CH3 groups
- Dramatically simplifies structure determination by providing a direct C-H correlation map
- Compatible with 13C isotopic labeling, enabling selective tracking of metabolic pathways
- Phase and multiplicity information can distinguish CH3 and CH from CH2 groups in phase-edited variants
- Requires 13C signal: at natural abundance (1.1%), sensitivity is lower than proton NMR; many applications use isotopic enrichment
- Long acquisition times for large molecules with many carbons; spectral crowding is still possible despite dimensionality increase
- One-bond coupling is detected; longer-range C-H correlations (2JCH, 3JCH) are suppressed, limiting 3D structure information
- Quaternary carbons are invisible, requiring complementary HMBC or INADEQUATE experiments for complete carbon assignment
Frequently asked
How is HSQC different from HMQC or HMBC?
HSQC detects one-bond C-H coupling (1JCH, ~150 Hz); HMQC is an older variant also detecting 1JCH; HMBC detects longer-range couplings (2JCH and 3JCH). HSQC is faster and more sensitive. HMBC reveals quaternary carbons and provides longer-range connectivity information but has lower resolution.
Why do quaternary carbons not appear in HSQC?
HSQC transfers magnetization between protons and their attached carbons via one-bond coupling. Quaternary carbons have no attached protons, so there is no 1JCH coupling to transfer magnetization. Detecting quaternary carbons requires techniques like HMBC or direct 13C observation.
Can HSQC distinguish CH3, CH2, and CH groups?
Standard HSQC cannot directly distinguish them because it shows only the correlation, not multiplicity. Phase-edited HSQC variants (edited HSQC or DEPT-HSQC) encode multiplicity information, typically showing CH and CH3 pointing up and CH2 pointing down (or inverted depending on pulse design).
Sources
- Bodenhausen, G., & Ruben, D. J. (1981). Natural abundance nitrogen-15 NMR by enhanced heteronuclear spectroscopy. Chemical Physics Letters, 69(2), 185-189. DOI: 10.1016/0009-2614(80)80041-8 ↗
- Patt, S. L., & Shoolery, J. N. (1992). Attached proton test (APT). Journal of Magnetic Resonance, 46(3), 535-539. link ↗
- Bax, A., Griffey, R. H., & Hawkins, B. L. (1983). Correlation of proton and nitrogen-15 chemical shifts by heteronuclear multiquantum NMR. Journal of the American Chemical Society, 105(24), 7188-7190. link ↗
How to cite this page
ScholarGate. (2026, June 3). Heteronuclear Single-Quantum Coherence. ScholarGate. https://scholargate.app/en/spectroscopy/hsqc
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