{"title":"A solid-state NMR approach for distinguishing between RNH2 and RNH3+ sites","authors":"Riley Nickles , Emily C. Heider , James K. Harper","doi":"10.1016/j.ssnmr.2025.102018","DOIUrl":null,"url":null,"abstract":"<div><div>A necessary step in characterizing solid-phase organic materials is the accurate assignment of the ionization state at acidic and basic sites. Solution phase pK<sub>a</sub>'s are not always reliable reference points because local environments can significantly change pK<sub>a</sub> values in solids. Herein, an approach for distinguishing R–NH<sub>2</sub> and R–NH<sub>3</sub><sup>+</sup> is described based on experimental <sup>15</sup>N chemical shift tensors principal values for a given site (i.e. <em>δ</em><sub>11</sub>, <em>δ</em><sub>22</sub> and <em>δ</em><sub>33</sub>) from 18 model compounds. Those <sup>15</sup>N sites that are present as R–NH<sub>3</sub><sup>+</sup> have anisotropies between 5 and 15 ppm. In contrast, all R–NH<sub>2</sub> sites have anisotropies between 14 and 115 ppm. These R–NH<sub>2</sub> moieties can be further categorized into three subgroups. The differences observed are postulated to arise from differences in the symmetry of the intermolecular hydrogen bonding environment, or the direct attachment of the NH<sub>2</sub> to an aromatic ring.</div></div>","PeriodicalId":21937,"journal":{"name":"Solid state nuclear magnetic resonance","volume":"138 ","pages":"Article 102018"},"PeriodicalIF":2.4000,"publicationDate":"2025-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Solid state nuclear magnetic resonance","FirstCategoryId":"92","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0926204025000347","RegionNum":3,"RegionCategory":"化学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"CHEMISTRY, PHYSICAL","Score":null,"Total":0}
引用次数: 0
Abstract
A necessary step in characterizing solid-phase organic materials is the accurate assignment of the ionization state at acidic and basic sites. Solution phase pKa's are not always reliable reference points because local environments can significantly change pKa values in solids. Herein, an approach for distinguishing R–NH2 and R–NH3+ is described based on experimental 15N chemical shift tensors principal values for a given site (i.e. δ11, δ22 and δ33) from 18 model compounds. Those 15N sites that are present as R–NH3+ have anisotropies between 5 and 15 ppm. In contrast, all R–NH2 sites have anisotropies between 14 and 115 ppm. These R–NH2 moieties can be further categorized into three subgroups. The differences observed are postulated to arise from differences in the symmetry of the intermolecular hydrogen bonding environment, or the direct attachment of the NH2 to an aromatic ring.
期刊介绍:
The journal Solid State Nuclear Magnetic Resonance publishes original manuscripts of high scientific quality dealing with all experimental and theoretical aspects of solid state NMR. This includes advances in instrumentation, development of new experimental techniques and methodology, new theoretical insights, new data processing and simulation methods, and original applications of established or novel methods to scientific problems.