In the presence of a small amount of acid, a solution of acetaldehyde (CH3CHO) in methanol...

In the presence of a small amount of acid, a solution of acetaldehyde (CH3CHO) in methanol (CH3OH) was allowed to stand and a new compound L was formed. L has a molecular ion in its mass spectrum at 90 and IR absorptions at 2992 and 2941 cm−1. L shows three signals in its 13C NMR at 19, 52, and 101 ppm. The 1H NMR spectrum of L is given below. What is the structure of L?