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Despite their importance the light nature of the proton makes characterization of acid\u2013base aggregates challenging. Here, we track such acid\u2013base interactions over a broad range of relative compositions between diphenyl phosphoric acid and the base quinaldine in dichloromethane, by using a combination of dielectric relaxation and NMR spectroscopy. In contrast to what one would expect for an acid\u2013base titration, we find strong deviations from quantitative proton transfer from the acid to the base. Even for an excess of the base, multimers consisting of one base and at least two acid molecules are formed, in addition to the occurrence of proton transfer from the acid to the base and simultaneous formation of ion pairs. For equimolar mixtures such multimers constitute about one third of all intermolecular aggregates. Quantitative analysis of our results shows that the acid\u2010base association constant is only around six times larger than that for the acid binding to an acid\u2010base dimer, that is, to an already protonated base. Our findings have implications for the interpretation of previous studies of reactive intermediates in organocatalysis and provide a rationale for previously observed nonlinear effects in phosphoric acid catalysis.<\/jats:p>","DOI":"10.1002\/chem.201701576","type":"journal-article","created":{"date-parts":[[2017,6,8]],"date-time":"2017-06-08T23:58:46Z","timestamp":1496966326000},"page":"10853-10860","source":"Crossref","is-referenced-by-count":15,"title":["Complexity in Acid\u2013Base Titrations: Multimer Formation Between Phosphoric Acids and Imines"],"prefix":"10.1002","volume":"23","author":[{"given":"Christian","family":"Malm","sequence":"first","affiliation":[{"name":"Department of Molecular Spectroscopy Max Planck Institute for Polymer Research  Ackermannweg 10 55128 Mainz Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Heejae","family":"Kim","sequence":"additional","affiliation":[{"name":"Department of Molecular Spectroscopy Max Planck Institute for Polymer Research  Ackermannweg 10 55128 Mainz Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Manfred","family":"Wagner","sequence":"additional","affiliation":[{"name":"Department of Molecular Spectroscopy Max Planck Institute for Polymer Research  Ackermannweg 10 55128 Mainz Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4419-5220","authenticated-orcid":false,"given":"Johannes","family":"Hunger","sequence":"additional","affiliation":[{"name":"Department of Molecular Spectroscopy Max Planck Institute for Polymer Research  Ackermannweg 10 55128 Mainz Germany"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"311","published-online":{"date-parts":[[2017,7,24]]},"reference":[{"key":"e_1_2_7_1_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja01603a022"},{"key":"e_1_2_7_2_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja039280j"},{"key":"e_1_2_7_3_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja953445"},{"key":"e_1_2_7_4_1","doi-asserted-by":"publisher","DOI":"10.1002\/anie.200806181"},{"key":"e_1_2_7_4_2","doi-asserted-by":"publisher","DOI":"10.1002\/ange.200806181"},{"key":"e_1_2_7_5_1","doi-asserted-by":"publisher","DOI":"10.1039\/p29820001333"},{"key":"e_1_2_7_6_1","doi-asserted-by":"publisher","DOI":"10.1039\/C6CP06677A"},{"key":"e_1_2_7_7_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja400611x"},{"key":"e_1_2_7_8_1","doi-asserted-by":"publisher","DOI":"10.1016\/S0022-2860(03)00086-3"},{"key":"e_1_2_7_9_1","doi-asserted-by":"publisher","DOI":"10.1021\/jacs.6b09244"},{"key":"e_1_2_7_10_1","doi-asserted-by":"publisher","DOI":"10.1002\/anie.201101385"},{"key":"e_1_2_7_10_2","doi-asserted-by":"publisher","DOI":"10.1002\/ange.201101385"},{"key":"e_1_2_7_11_1","doi-asserted-by":"publisher","DOI":"10.1021\/acscatal.5b01694"},{"key":"e_1_2_7_12_1","doi-asserted-by":"publisher","DOI":"10.1039\/c3sc52142g"},{"key":"e_1_2_7_13_1","doi-asserted-by":"publisher","DOI":"10.1021\/jacs.6b09243"},{"key":"e_1_2_7_14_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja0728223"},{"key":"e_1_2_7_15_1","doi-asserted-by":"publisher","DOI":"10.1063\/1.468678"},{"key":"e_1_2_7_16_1","doi-asserted-by":"publisher","DOI":"10.1038\/nature07367"},{"key":"e_1_2_7_17_1","doi-asserted-by":"publisher","DOI":"10.1002\/anie.201205449"},{"key":"e_1_2_7_17_2","doi-asserted-by":"publisher","DOI":"10.1002\/ange.201205449"},{"key":"e_1_2_7_18_1","doi-asserted-by":"publisher","DOI":"10.1021\/cr5001496"},{"key":"e_1_2_7_19_1","doi-asserted-by":"publisher","DOI":"10.1002\/anie.200353240"},{"key":"e_1_2_7_19_2","doi-asserted-by":"publisher","DOI":"10.1002\/ange.200353240"},{"key":"e_1_2_7_20_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.tetlet.2006.11.017"},{"key":"e_1_2_7_21_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja3122137"},{"key":"e_1_2_7_22_1","doi-asserted-by":"publisher","DOI":"10.1002\/chem.200800890"},{"key":"e_1_2_7_23_1","doi-asserted-by":"publisher","DOI":"10.1021\/acs.accounts.6b00052"},{"key":"e_1_2_7_24_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja800793t"},{"key":"e_1_2_7_25_1","doi-asserted-by":"publisher","DOI":"10.1126\/science.1261043"},{"key":"e_1_2_7_26_1","doi-asserted-by":"publisher","DOI":"10.1055\/s-2005-872251"},{"key":"e_1_2_7_27_1","doi-asserted-by":"publisher","DOI":"10.1007\/978-3-642-56120-7"},{"key":"e_1_2_7_28_1","doi-asserted-by":"publisher","DOI":"10.1351\/pac200880061239"},{"key":"e_1_2_7_29_1","doi-asserted-by":"publisher","DOI":"10.1039\/c0cp01120g"},{"key":"e_1_2_7_30_1","doi-asserted-by":"publisher","DOI":"10.1002\/anie.201602769"},{"key":"e_1_2_7_30_2","doi-asserted-by":"publisher","DOI":"10.1002\/ange.201602769"},{"key":"e_1_2_7_31_1","doi-asserted-by":"publisher","DOI":"10.1088\/0957-0233\/24\/1\/012005"},{"key":"e_1_2_7_32_1","doi-asserted-by":"publisher","DOI":"10.1109\/19.676718"},{"key":"e_1_2_7_33_1","doi-asserted-by":"publisher","DOI":"10.1021\/jp312623p"},{"key":"e_1_2_7_34_1","doi-asserted-by":"publisher","DOI":"10.1088\/0957-0233\/7\/4\/010"},{"key":"e_1_2_7_35_1","doi-asserted-by":"publisher","DOI":"10.1039\/C4CP02709D"},{"key":"e_1_2_7_36_1","doi-asserted-by":"publisher","DOI":"10.1021\/ja00334a013"},{"key":"e_1_2_7_37_1","doi-asserted-by":"publisher","DOI":"10.1002\/anie.200600191"},{"key":"e_1_2_7_37_2","doi-asserted-by":"publisher","DOI":"10.1002\/ange.200600191"},{"key":"e_1_2_7_38_1","doi-asserted-by":"publisher","DOI":"10.1039\/b906555p"},{"key":"e_1_2_7_39_1","doi-asserted-by":"publisher","DOI":"10.1016\/j.cplett.2009.02.024"},{"key":"e_1_2_7_40_1","volume-title":"Theory 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