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The enol has a hydrogen bond to the nitrogen of the secondary amine. The structure was investigated by nuclear magnetic resonance and deuterium isotope effects on <jats:sup>13<\/jats:sup>C chemical shifts as well as with density functional theory calculations to study the changed hydrogen bond pattern. It was found that the hydrogen bond involving the OH\u20109 group in chloroform forms a strong hydrogen bond than in usnic acid itself and that this hydrogen bond becomes even stronger in the more polar solvent, dimethylsulfoxide. Tautomerism was observed in the Mannich base as demonstrated by deuterium isotope effects on chemical shifts. The position of the tautomeric equilibrium depends on the solvent, and the position of the equilibrium governs the strength of the OH\u20109\u2026O\u2550C hydrogen bond.<\/jats:p>","DOI":"10.1002\/mrc.4760","type":"journal-article","created":{"date-parts":[[2018,6,19]],"date-time":"2018-06-19T13:16:14Z","timestamp":1529414174000},"page":"1094-1100","update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":2,"title":["Structure of a new usnic acid derivative from a deacylating Mannich reaction: NMR studies supported by theoretical calculations of chemical shifts"],"prefix":"10.1002","volume":"56","author":[{"given":"Huong Giang Thi","family":"Nguyen","sequence":"first","affiliation":[{"name":"Institute of Drug Quality Control  Ho Chi Minh City Vietnam"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Vinh Ngoc","family":"Nguyen","sequence":"additional","affiliation":[{"name":"Institute of Drug Quality Control  Ho Chi Minh City Vietnam"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Fadhil S.","family":"Kamounah","sequence":"additional","affiliation":[{"name":"Department of Chemistry University of Copenhagen  Copenhagen Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4751-9910","authenticated-orcid":false,"given":"Poul Erik","family":"Hansen","sequence":"additional","affiliation":[{"name":"Department of Science and Environment Roskilde University  Roskilde Denmark"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2018,7,2]]},"reference":[{"key":"e_1_2_6_2_1","first-page":"903","volume":"24","author":"Hansen P. 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