{"term":{"id":"08352","title":"heteronuclear multiple bond correlation NMR","longtitle":"IUPAC Gold Book - heteronuclear multiple bond correlation NMR","doi":"10.1351\/goldbook.08352","code":"08352","status":"current","initialism":"<em>initialism<\/em>: HMBC","definitions":[{"id":1,"text":"Two-dimensional nuclear magnetic resonance spectroscopy that gives correlations between carbons and protons that are separated by two, three, and, sometimes in conjugated systems, four bonds.","notes":{"1":"Direct one-bond correlations are suppressed.","2":"HMBC gives connectivity information much like a proton-proton COSY.","3":"The intensity of cross peaks depends on the spin-spin coupling constant, which for three-bond couplings follows the Karplus relationship. For dihedral angles near \\(\\pu{90\\!^{\\circ}}\\), the coupling is near zero. Thus, the absence of a cross peak does not confirm that carbon-proton pairs are many bonds apart.","4":"Because of the wide range (\\(\\pu{0}\\) to \\(\\pu{14 Hz}\\)) of possible carbon-proton couplings, two experiments are often performed. One optimized for \\(\\pu{5 Hz}\\) couplings and the second optimized for \\(\\pu{10 Hz}\\). This gives the optimum signal-to-noise ratio. Alternatively, a comprise value of \\(\\pu{7}\\) to \\(\\pu{8 Hz}\\) can be used. There are also \"accordion\" versions that attempt to sample the full range of couplings."},"links":[{"term":"Two-dimensional nuclear magnetic resonance spectroscopy","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08439"},{"term":"signal-to-noise ratio","url":"https:\/\/goldbook.iupac.org\/\/terms\/view\/08282"}],"sources":["PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 690 (https:\/\/doi.org\/10.1515\/pac-2019-0203)"]}],"altoutputs":{"html":"https:\/\/goldbook.iupac.org\/terms\/view\/08352\/html","xml":"https:\/\/goldbook.iupac.org\/terms\/view\/08352\/xml","plain":"https:\/\/goldbook.iupac.org\/terms\/view\/08352\/plain"},"citation":"Citation: 'heteronuclear multiple bond correlation NMR' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351\/goldbook.08352","license":"The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0\/) for individual terms.","collection":"If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .","disclaimer":"The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.","accessed":"2026-06-11T01:25:48+00:00"}}