May 8, 2008
Methoxy groups have a distinct NMR signature that make them easy to spot in virtually every case. The basic pattern is a singlet integrating to 3 and ranging between 2.4 to 4.4 ppm on a 1H NMR spectrum (assuming no overlap with other resonances). On the 13C end, a 13C resonance is seen between 46 and 69 ppm. In addition, when an elucidator is working on narrowing down a molecular formula (MF) for an unknown sample, the prospect of OCH3 information helps in the minimum oxygen count.
The 1H -13C DEPT-HSQC spectrum below shows two OCH3 groups. The singlet integrating to 3 in the 1H NMR spectrum and the carbon information from the DEPT-HSQC at ~56 ppm. With this information on hand, the minimum atom count for the MF is C2H6O2.