Provide a structure for the following compound: EI mass spectrum: two molecular ions of about equal intensity at m/z = 180 and 182; IR: 1740 cm-1; 1H NMR: ? 1.30 (3H, t J = 7 Hz); ? 1.80 (3H, d, J = 7 Hz); ? 4.23 (2H, q, J = 7 Hz); ? 4.37 (1H, q, J = 7 Hz).