Methoxy group, proton chemical shift

The third compound to be isolated from ozonations of Feists ester was V. Its NMR spectrum was of prime importance in establishing its structure. Other than the methoxy signal at 3.67 ppm, the outstanding feature of the spectrum was the presence of two sets of AB doublets with chemical shifts for the four protons at 3.33, 3.23, 2.90, and 2.72 ppm. The ratio of peak intensities was 6 1 1 1 1 for the five types of protons. In the spectrum of the dideutero derivative, the AB pattern at high field was not present, showing that these high field protons were those a to the carbomethoxy groups. 

Chemical shifts of the methyl protons (t= 7.41-7.64) are in the sequence 3-methyl 6-methyl < 5-methyl 4-methyl and those of the methoxy group (t = 5.82-6.07) are in the sequence of 3-methoxy < 6-methoxy <4-methoxy. The spin-spin coupling constants are J= 5.3-6, J35 = 2.0-3.7, J3a = 0.5-1.0, J45 = 8.0-8.8, 46 = 0.7-1.0, and Jga = 5.8-7.0. Long-range coupling constants between methyl protons and protons attached to the ortho ring carbon are smaller than 1 cps. 

---