Incorrect assignments for the carbon-13 signals of 2-nitroaniline appeared in online databases for many years. This is because they were based on group additivity assumptions rather than on experimental facts. 2D-NMR studies can easily establish the correct order of peaks in the aromatic region. In cases where additivity fails, quantum mechanical calculations can offer insight into the interactions at work. We describe an exercise where students correctly assign the carbon-13 spectrum of an aromatic compound with two or three substituents on the ring. We discuss several interesting cases including substituted indans in which the fused ring induces strain into the aromatic unit. A Bruker 300 MHz instrument is used to collect all spectra. Gaussian09 (www.gaussian.com) is used for the calculations and the software is made accessible to the students through a web browser (www.webmo.net). The work is supported by the Fordham University Research Council and by an NSF instrumentation grant.

NMR measurements coupled with quantum mechanical calculations for assigning carbon-13 NMR signals in the undergraduate curriculum

241st National Meeting (2011)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.